This document discusses the nature and properties of viruses. It defines viruses as obligate intracellular parasites that consist of nucleic acid genomes enclosed in protein capsids. Viruses can have DNA or RNA genomes, and they require host cells to replicate as they lack their own metabolic machinery. The document outlines the virus replication cycle and explains how viruses enter cells, express their genes, replicate their genomes, and assemble new virus particles. It also discusses why viruses are important to study due to their ability to cause diseases in humans, animals and plants.
Viruses infect host cells and use the host's cellular machinery to replicate themselves. This involves the virus attaching and entering the host cell, releasing its genome, producing new viral components, assembling new virus particles, and causing the host cell to burst and release the new virus particles to infect other cells. Viruses can spread systemically throughout the host's body or remain localized to sites of infection. The replication cycle allows viruses to efficiently propagate and spread infection.
Viral assays allow for quantifying the number of animal viruses. While bacterial viruses can easily be grown, growing animal viruses is more difficult and expensive, often requiring whole animals or embryonating eggs. When animal cells grow as monolayers, a plaque assay can be used to count viruses by serially diluting the virus in a liquid medium and adding it to separate plates with monolayers of tissue culture cells. After the viruses attach, a semi-solid medium is added to restrict virus movement and allow only adjacent cells to become infected, forming visible plaques that can be counted.
Viruses rely on host cells to replicate as they cannot do so independently. There are six basic stages of viral replication: 1) attachment to host cell receptors, 2) penetration of the host cell, 3) uncoating of the viral capsid, 4) replication of viral genetic material and proteins, 5) assembly of new viral particles, and 6) release of new virus particles through lysis or budding. The replication process differs between DNA and RNA viruses as well as between viruses with positive-sense and negative-sense genomes, but generally involves the virus taking over host cell machinery to produce more viruses and spread infection.
This document discusses virus classification systems. It provides an overview of the Baltimore classification system, which categorizes viruses based on their method of mRNA production. Group I viruses contain double-stranded DNA and produce mRNA through transcription. Group II viruses have single-stranded DNA and produce a double-stranded DNA intermediate before transcription. Group III viruses use double-stranded RNA, with one strand serving as the mRNA template. Group IV viruses contain single-stranded RNA with positive polarity that directly serves as mRNA.
Cauliflower Mosaic Virus is a pararetrovirus that infects plants in the brassicaceae family like cauliflower. It has an icosahedral capsid containing a circular double stranded DNA genome around 80kb in size. The virus replicates through reverse transcription, with its DNA entering the nucleus and being transcribed by the host polymerase. The virus has several open reading frames that encode for structural, movement and other proteins. While it can be used as a vector to insert foreign genes into plants, its capacity is limited to a few hundred nucleotides before the foreign DNA is expelled.
Viruses are obligate intracellular parasites that contain either DNA or RNA. They replicate through a series of steps within a host cell. There are two main viral life cycles: lytic and lysogenic. The lytic cycle involves virus replication, assembly, and lysis of the host cell. The lysogenic cycle involves integration of the viral genome into the host cell genome without immediate cell lysis. Viruses are also classified based on their genome type and replication strategy, such as retroviruses which contain RNA and replicate through a DNA intermediate.
Viruses infect host cells and use the host's cellular machinery to replicate themselves. This involves the virus attaching and entering the host cell, releasing its genome, producing new viral components, assembling new virus particles, and causing the host cell to burst and release the new virus particles to infect other cells. Viruses can spread systemically throughout the host's body or remain localized to sites of infection. The replication cycle allows viruses to efficiently propagate and spread infection.
Viral assays allow for quantifying the number of animal viruses. While bacterial viruses can easily be grown, growing animal viruses is more difficult and expensive, often requiring whole animals or embryonating eggs. When animal cells grow as monolayers, a plaque assay can be used to count viruses by serially diluting the virus in a liquid medium and adding it to separate plates with monolayers of tissue culture cells. After the viruses attach, a semi-solid medium is added to restrict virus movement and allow only adjacent cells to become infected, forming visible plaques that can be counted.
Viruses rely on host cells to replicate as they cannot do so independently. There are six basic stages of viral replication: 1) attachment to host cell receptors, 2) penetration of the host cell, 3) uncoating of the viral capsid, 4) replication of viral genetic material and proteins, 5) assembly of new viral particles, and 6) release of new virus particles through lysis or budding. The replication process differs between DNA and RNA viruses as well as between viruses with positive-sense and negative-sense genomes, but generally involves the virus taking over host cell machinery to produce more viruses and spread infection.
This document discusses virus classification systems. It provides an overview of the Baltimore classification system, which categorizes viruses based on their method of mRNA production. Group I viruses contain double-stranded DNA and produce mRNA through transcription. Group II viruses have single-stranded DNA and produce a double-stranded DNA intermediate before transcription. Group III viruses use double-stranded RNA, with one strand serving as the mRNA template. Group IV viruses contain single-stranded RNA with positive polarity that directly serves as mRNA.
Cauliflower Mosaic Virus is a pararetrovirus that infects plants in the brassicaceae family like cauliflower. It has an icosahedral capsid containing a circular double stranded DNA genome around 80kb in size. The virus replicates through reverse transcription, with its DNA entering the nucleus and being transcribed by the host polymerase. The virus has several open reading frames that encode for structural, movement and other proteins. While it can be used as a vector to insert foreign genes into plants, its capacity is limited to a few hundred nucleotides before the foreign DNA is expelled.
Viruses are obligate intracellular parasites that contain either DNA or RNA. They replicate through a series of steps within a host cell. There are two main viral life cycles: lytic and lysogenic. The lytic cycle involves virus replication, assembly, and lysis of the host cell. The lysogenic cycle involves integration of the viral genome into the host cell genome without immediate cell lysis. Viruses are also classified based on their genome type and replication strategy, such as retroviruses which contain RNA and replicate through a DNA intermediate.
Concept of virology
Viruses
Types of viruses
Viral characteristics
Virion
Size and Shape
Structure
Replication
Viral Variation
Classification
Quiz
BEST OF LUCK
This document discusses the bacterial virus Phi X 174 phage. It begins with an introduction to bacteriophages and their discovery. It then provides the taxonomic classification of Phi X 174, placing it in the family Microviridae. The document outlines the history of Phi X 174, including its early study and sequencing. It describes the morphology and genome organization of Phi X 174, including its circular single-stranded DNA genome of 5386 nucleotides that encodes 10 genes and 11 proteins. The life cycle of Phi X 174 is summarized, from attachment and entry, to replication, assembly of mature virions, and release through cell lysis.
The document provides a brief history of smallpox and the development of vaccination. It describes how Edward Jenner used cowpox pus to inoculate and prevent smallpox in the 18th century. It then summarizes the World Health Organization's smallpox eradication program from 1967 to 1979 and contemporary concerns about smallpox being used for bioterrorism.
Bacterial virus (Bacteriophage).
Structure of bacteriophage.
Where we can find phage?
Families of bacteriophage.
Life cycle of bacteriophage.
Potential uses of bacteriophage.
Bacteriophage vs. antibiotics.
Factors affecting phage therapy.
CaMV Genome organization & their replication, Cauliflower Mosaic Virus belong to Group VII (ds-DNA-RT), Open circular double stranded DNA of 80kb and CaMV replicates by reverse transcription
Viruses come in a variety of shapes and sizes, with the main morphological types being helical, icosahedral, prolate, enveloped, and complex. They are composed of a nucleic acid core surrounded by a protein capsid, and some have an additional outer envelope. Viruses infect all types of living organisms by introducing their genetic material inside host cells and hijacking the cells' machinery to replicate themselves.
The document discusses the structure, classification, and replication of viruses. It begins by describing different viral structural components, including the capsid, envelope, and nucleic acid core. Viruses are classified based on their nucleic acid composition and structure, focusing on whether they have DNA or RNA genomes and whether they are enveloped or not. The document also examines different capsid structures like icosahedral, helical, and complex shapes. It provides examples of representative virus families and discusses how viruses are named.
Animal viruses are self replicating, intracellular parasites that completely rely on host animal cell for reproduction. They use the host's cellular components to replicate, then leaves the host cell to infect other cells.
Picorna viruses include poliovirus, coxsackie virus, echovirus, rhinovirus, and others. They are small, non-enveloped viruses with positive-sense RNA genomes. Poliovirus causes the disease poliomyelitis. It is transmitted fecally-orally and can infect the central nervous system, causing paralysis. Vaccines including both live attenuated (OPV) and killed (IPV) versions have been highly effective in polio's global eradication efforts. Rhinoviruses are the most common cause of the common cold.
This document discusses virus taxonomy and classification. It provides:
1. An overview of virus classification systems, which are primarily based on phenotypic characteristics like morphology, nucleic acid type, host, and disease symptoms.
2. A history of virus naming conventions from early systems based on host names to current standardized systems like ICTV and Baltimore classifications.
3. Details on the International Committee on Taxonomy of Viruses (ICTV) which develops agreed-upon virus taxonomy, names, and classifications communicated internationally.
Viruses exist at the boundary between living and non-living things. They consist of nucleic acids and proteins but cannot reproduce outside of a host cell. Viruses come in different shapes and sizes and have unique structures suited to their method of infection. They hijack the machinery of living cells to reproduce either through lytic or lysogenic cycles, ultimately resulting in the destruction of the host cell. While viruses rely on host cells, they are not considered alive as they do not have their own metabolism or respond to their environment.
Virology is the study of viruses and virus-like agents, including their taxonomy, disease-producing properties, culture, and genetics. Viruses are non-cellular biological entities that consist of DNA or RNA genomes enclosed in a protein coat. They can only reproduce within living cells. Influenza is caused by RNA viruses of the Orthomyxoviridae family. There are three main types of influenza viruses - A, B, and C. Influenza A is further classified into subtypes based on surface proteins and can infect both humans and animals. Influenza causes respiratory illness with symptoms like fever, cough and sore throat. It spreads through respiratory droplets and the best prevention is an annual flu vaccine.
1) Viruses are non-living infectious particles that contain genetic material and a protein coat called a capsid. 2) Viruses can only replicate inside a host cell by injecting their genetic material and using the host cell's machinery. 3) Viruses exist in two states - as active viruses when infecting a host cell, or dormant virions when not in contact with a host.
Cultivation of viruses uhf copy - copyheena thakur
This document discusses viruses and methods for cultivating viruses. It describes viruses as obligate intracellular parasites that can only multiply inside living host cells. The three main methods for cultivating viruses discussed are inoculation of viruses into animals, embryonated eggs, and tissue culture. For animal inoculation, mice are commonly used and viruses can be introduced via different routes. Embryonated eggs provide a suitable environment for virus growth and isolation. Tissue culture involves culturing cells or tissue fragments, and cell lines provide indefinite growth. Detection of virus growth involves monitoring for cytopathic effects, hemadsorption, interference, and other methods.
Presentation comprises of introductory information on virus, related terminology, its composition and structure, classification, nomenclature and taxonomy for under graduate students.
This document provides an overview of viruses and their structure and life cycle. It discusses:
1. The history of virus discovery and early research showing that viruses are smaller than bacteria and can pass through filters.
2. The basic structure of viruses, which typically includes a protein capsid enclosing nucleic acids, and some viruses having an outer envelope.
3. The virus life cycle, which generally involves adsorption to a host cell, penetration, replication of viral components, assembly of new virus particles, and release through budding or cell lysis.
Viruses are defined as nucleoprotein complexes that infect host cells and use their metabolic processes to replicate. They are the smallest known infectious agents and are metabolically inert outside of host cells, requiring entry into a host cell to replicate. Viruses come in different structures with either DNA or RNA genomes and may have capsids alone or capsids surrounded by envelopes. They infect bacteria, plants, animals, and humans by invading cells and forcing them to produce new virus copies until the cell lyses.
This document classifies viruses into 7 groups based on their nucleic acid composition and transcription mechanism:
1. Group 1 contains dsDNA viruses like adenoviruses and herpes viruses. mRNA is synthesized using the dsDNA genome as a template.
2. Group 2 contains ssDNA viruses like parvoviruses.
3. Group 3 contains (+) sense ssRNA viruses which replicate in the cytoplasm, such as coronaviruses, picornaviruses, and togaviruses that cause diseases.
4. Group 4 contains (-) sense ssRNA viruses like rhabdoviruses and orthomyxoviruses.
5. Group 5 contains dsRNA
Viruses are the smallest infectious agents that can only replicate inside living cells. They contain either DNA or RNA surrounded by a protein coat called a capsid. Some viruses have an outer envelope. Viruses infect cells by binding to receptors on the cell surface and releasing their genetic material inside. The genetic material is then used to hijack the cell's machinery to produce new viral components and assemble new virus particles, which are then released to infect other cells. Viruses are classified based on their structure, genome, proteins, and pathogenicity. Their rapid replication within host cells allows viruses to spread efficiently between individuals.
A virion is the complete, infectious form of a virus outside of a host cell. It consists of a core of RNA or DNA protected by a protein capsid. Most plant viruses have a rod-shaped virion structure with a naked cylindrical capsid. While a virion infects all types of organisms, a viroid only infects plants. Key features of a virion are that it becomes inactivated when exposed to solvents like chloroform and it has an icosahedral shape with 20 triangular faces in its capsid. Both viruses and virions are non-cellular, obligate parasites that consist of DNA or RNA and can act as infectious agents in a host-specific manner.
The document provides information about viruses, including their structure, classification, and life cycles. It describes that viruses are non-living particles composed of genetic material and protein that can infect host cells. Viruses come in different shapes and sizes, and some have envelopes while others do not. They are classified based on their genetic material and hosts. The document also explains the lytic and lysogenic life cycles of bacteriophages and how they reproduce and infect bacterial cells.
The document provides information about viruses, including:
i. Viruses are genetic elements enclosed in protein that can only reproduce inside living host cells. They were first observed for their ability to cause disease in the late 19th century.
ii. Viruses are composed of a protein coat called a capsid that encloses their genetic material of either DNA or RNA. They vary greatly in size and shape.
iii. Viruses can only reproduce by taking over the cellular machinery of host cells and forcing the cells to produce new virus particles. Their replication cycles involve adsorption to host cells, penetration of the cells, synthesis of new viral components, assembly of new virus particles, and release of progeny viruses.
Concept of virology
Viruses
Types of viruses
Viral characteristics
Virion
Size and Shape
Structure
Replication
Viral Variation
Classification
Quiz
BEST OF LUCK
This document discusses the bacterial virus Phi X 174 phage. It begins with an introduction to bacteriophages and their discovery. It then provides the taxonomic classification of Phi X 174, placing it in the family Microviridae. The document outlines the history of Phi X 174, including its early study and sequencing. It describes the morphology and genome organization of Phi X 174, including its circular single-stranded DNA genome of 5386 nucleotides that encodes 10 genes and 11 proteins. The life cycle of Phi X 174 is summarized, from attachment and entry, to replication, assembly of mature virions, and release through cell lysis.
The document provides a brief history of smallpox and the development of vaccination. It describes how Edward Jenner used cowpox pus to inoculate and prevent smallpox in the 18th century. It then summarizes the World Health Organization's smallpox eradication program from 1967 to 1979 and contemporary concerns about smallpox being used for bioterrorism.
Bacterial virus (Bacteriophage).
Structure of bacteriophage.
Where we can find phage?
Families of bacteriophage.
Life cycle of bacteriophage.
Potential uses of bacteriophage.
Bacteriophage vs. antibiotics.
Factors affecting phage therapy.
CaMV Genome organization & their replication, Cauliflower Mosaic Virus belong to Group VII (ds-DNA-RT), Open circular double stranded DNA of 80kb and CaMV replicates by reverse transcription
Viruses come in a variety of shapes and sizes, with the main morphological types being helical, icosahedral, prolate, enveloped, and complex. They are composed of a nucleic acid core surrounded by a protein capsid, and some have an additional outer envelope. Viruses infect all types of living organisms by introducing their genetic material inside host cells and hijacking the cells' machinery to replicate themselves.
The document discusses the structure, classification, and replication of viruses. It begins by describing different viral structural components, including the capsid, envelope, and nucleic acid core. Viruses are classified based on their nucleic acid composition and structure, focusing on whether they have DNA or RNA genomes and whether they are enveloped or not. The document also examines different capsid structures like icosahedral, helical, and complex shapes. It provides examples of representative virus families and discusses how viruses are named.
Animal viruses are self replicating, intracellular parasites that completely rely on host animal cell for reproduction. They use the host's cellular components to replicate, then leaves the host cell to infect other cells.
Picorna viruses include poliovirus, coxsackie virus, echovirus, rhinovirus, and others. They are small, non-enveloped viruses with positive-sense RNA genomes. Poliovirus causes the disease poliomyelitis. It is transmitted fecally-orally and can infect the central nervous system, causing paralysis. Vaccines including both live attenuated (OPV) and killed (IPV) versions have been highly effective in polio's global eradication efforts. Rhinoviruses are the most common cause of the common cold.
This document discusses virus taxonomy and classification. It provides:
1. An overview of virus classification systems, which are primarily based on phenotypic characteristics like morphology, nucleic acid type, host, and disease symptoms.
2. A history of virus naming conventions from early systems based on host names to current standardized systems like ICTV and Baltimore classifications.
3. Details on the International Committee on Taxonomy of Viruses (ICTV) which develops agreed-upon virus taxonomy, names, and classifications communicated internationally.
Viruses exist at the boundary between living and non-living things. They consist of nucleic acids and proteins but cannot reproduce outside of a host cell. Viruses come in different shapes and sizes and have unique structures suited to their method of infection. They hijack the machinery of living cells to reproduce either through lytic or lysogenic cycles, ultimately resulting in the destruction of the host cell. While viruses rely on host cells, they are not considered alive as they do not have their own metabolism or respond to their environment.
Virology is the study of viruses and virus-like agents, including their taxonomy, disease-producing properties, culture, and genetics. Viruses are non-cellular biological entities that consist of DNA or RNA genomes enclosed in a protein coat. They can only reproduce within living cells. Influenza is caused by RNA viruses of the Orthomyxoviridae family. There are three main types of influenza viruses - A, B, and C. Influenza A is further classified into subtypes based on surface proteins and can infect both humans and animals. Influenza causes respiratory illness with symptoms like fever, cough and sore throat. It spreads through respiratory droplets and the best prevention is an annual flu vaccine.
1) Viruses are non-living infectious particles that contain genetic material and a protein coat called a capsid. 2) Viruses can only replicate inside a host cell by injecting their genetic material and using the host cell's machinery. 3) Viruses exist in two states - as active viruses when infecting a host cell, or dormant virions when not in contact with a host.
Cultivation of viruses uhf copy - copyheena thakur
This document discusses viruses and methods for cultivating viruses. It describes viruses as obligate intracellular parasites that can only multiply inside living host cells. The three main methods for cultivating viruses discussed are inoculation of viruses into animals, embryonated eggs, and tissue culture. For animal inoculation, mice are commonly used and viruses can be introduced via different routes. Embryonated eggs provide a suitable environment for virus growth and isolation. Tissue culture involves culturing cells or tissue fragments, and cell lines provide indefinite growth. Detection of virus growth involves monitoring for cytopathic effects, hemadsorption, interference, and other methods.
Presentation comprises of introductory information on virus, related terminology, its composition and structure, classification, nomenclature and taxonomy for under graduate students.
This document provides an overview of viruses and their structure and life cycle. It discusses:
1. The history of virus discovery and early research showing that viruses are smaller than bacteria and can pass through filters.
2. The basic structure of viruses, which typically includes a protein capsid enclosing nucleic acids, and some viruses having an outer envelope.
3. The virus life cycle, which generally involves adsorption to a host cell, penetration, replication of viral components, assembly of new virus particles, and release through budding or cell lysis.
Viruses are defined as nucleoprotein complexes that infect host cells and use their metabolic processes to replicate. They are the smallest known infectious agents and are metabolically inert outside of host cells, requiring entry into a host cell to replicate. Viruses come in different structures with either DNA or RNA genomes and may have capsids alone or capsids surrounded by envelopes. They infect bacteria, plants, animals, and humans by invading cells and forcing them to produce new virus copies until the cell lyses.
This document classifies viruses into 7 groups based on their nucleic acid composition and transcription mechanism:
1. Group 1 contains dsDNA viruses like adenoviruses and herpes viruses. mRNA is synthesized using the dsDNA genome as a template.
2. Group 2 contains ssDNA viruses like parvoviruses.
3. Group 3 contains (+) sense ssRNA viruses which replicate in the cytoplasm, such as coronaviruses, picornaviruses, and togaviruses that cause diseases.
4. Group 4 contains (-) sense ssRNA viruses like rhabdoviruses and orthomyxoviruses.
5. Group 5 contains dsRNA
Viruses are the smallest infectious agents that can only replicate inside living cells. They contain either DNA or RNA surrounded by a protein coat called a capsid. Some viruses have an outer envelope. Viruses infect cells by binding to receptors on the cell surface and releasing their genetic material inside. The genetic material is then used to hijack the cell's machinery to produce new viral components and assemble new virus particles, which are then released to infect other cells. Viruses are classified based on their structure, genome, proteins, and pathogenicity. Their rapid replication within host cells allows viruses to spread efficiently between individuals.
A virion is the complete, infectious form of a virus outside of a host cell. It consists of a core of RNA or DNA protected by a protein capsid. Most plant viruses have a rod-shaped virion structure with a naked cylindrical capsid. While a virion infects all types of organisms, a viroid only infects plants. Key features of a virion are that it becomes inactivated when exposed to solvents like chloroform and it has an icosahedral shape with 20 triangular faces in its capsid. Both viruses and virions are non-cellular, obligate parasites that consist of DNA or RNA and can act as infectious agents in a host-specific manner.
The document provides information about viruses, including their structure, classification, and life cycles. It describes that viruses are non-living particles composed of genetic material and protein that can infect host cells. Viruses come in different shapes and sizes, and some have envelopes while others do not. They are classified based on their genetic material and hosts. The document also explains the lytic and lysogenic life cycles of bacteriophages and how they reproduce and infect bacterial cells.
The document provides information about viruses, including:
i. Viruses are genetic elements enclosed in protein that can only reproduce inside living host cells. They were first observed for their ability to cause disease in the late 19th century.
ii. Viruses are composed of a protein coat called a capsid that encloses their genetic material of either DNA or RNA. They vary greatly in size and shape.
iii. Viruses can only reproduce by taking over the cellular machinery of host cells and forcing the cells to produce new virus particles. Their replication cycles involve adsorption to host cells, penetration of the cells, synthesis of new viral components, assembly of new virus particles, and release of progeny viruses.
This document provides an overview of viruses and their classification. It discusses that viruses consist of nucleic acid in a protein coat and can only reproduce within living host cells. Viruses vary in size and shape. The document then covers the discovery of viruses and their distinctive properties compared to living cells. It discusses the nomenclature and classification of viruses, including how they are classified based on their genome, structure, and hosts. Classification systems discussed include the LHT and Baltimore systems.
This document provides an overview of viruses, including their history of discovery, characteristics, components, shapes, classification, bacteriophages, replication cycles, enveloped viruses, and other related infectious agents like viroids and prions. It discusses key scientists and experiments that contributed to the understanding of viruses. The replication cycles of lytic and lysogenic bacteriophages as well as enveloped DNA and RNA viruses are described.
This presentation intends to explore the application of virus in different biomedical fields and research with special reference to vaccine production and plant viral diseases.
The lecture provided an overview of virology, focusing on the physical structure and chemical composition of viruses. It discussed that viruses are submicroscopic organisms containing genetic material within a protein coat. It described the main structures of viruses, including the capsid, envelope, and viral genomes which can be DNA or RNA. The lecture also explained that viruses are composed of mostly proteins, which can be structural or enzymatic, and that the viral proteins and nucleic acids determine how viruses infect and exploit host cells.
Viruses contain either DNA or RNA surrounded by a protein coat called a capsid. Some viruses have an outer envelope as well. Viruses infect host cells and use the cell's machinery to replicate their nucleic acid and proteins, eventually causing the cell to burst and release new virus particles. Viruses are classified based on their nucleic acid, replication strategy, and morphology. Common virus families include Herpesviridae, Retroviridae, and Adenoviridae. Viruses can cause disease through lytic infection cycles or establish latent or persistent infections. Some viruses are also associated with cancer development in hosts.
1. The document discusses the structure and replication cycle of viruses.
2. Viruses consist of genetic material (DNA or RNA) surrounded by a protein coat called a capsid, and some have an outer lipid envelope.
3. Viral replication involves the virus entering the host cell, expressing its genes to produce viral proteins and genetic material, assembling new virus particles, and exiting to infect new host cells.
This document provides an overview of microbiology and viruses. It discusses that viruses are obligatory intracellular parasites that contain either DNA or RNA and multiply by using the host cell's machinery. Viruses come in a variety of shapes and sizes, and infect specific host cells through attachment and receptors. They undergo replication cycles inside host cells and are then released through lysis or budding. The document also notes that some viruses can cause cancer by inserting oncogenes into host cell DNA and transforming normal cells into tumor cells.
01- General structure and classification of viruses1.pptxMaiBarakat8
This document discusses viruses and their structure and classification. It notes that viruses are smaller than bacteria, contain either DNA or RNA but not both, and consist of nucleic acid surrounded by a protein coat. Some key points made are that viruses replicate only inside living cells, have three symmetry types (cubic, helical, complex), and are classified into groups based on their nucleic acid and mRNA production methods. The stages of virus replication are also outlined.
Viruses are microscopic parasites that cannot reproduce outside of a host cell. They contain either DNA or RNA as their genetic material and have a protein capsid structure. Viruses are classified based on their morphology, chemical composition, and replication process. Examples of viruses include poliovirus, which causes polio and has a single-stranded RNA genome within a 30 nm protein capsid. Viruses fully depend on the host cell's machinery to express their genome and replicate.
Viruses exist in two phases - an extracellular phase where they possess few enzymes and protect their genome, and an intracellular phase where they induce host cells to synthesize viral components. They are cultivated using techniques like growing them in embryonated eggs, animal cell monolayers, and bacterial lawns. Viruses have a nucleocapsid core containing genetic material surrounded by a protein capsid. They vary greatly in size and structure, with capsids that are isocahedral, helical, enveloped, or more complex. Their genetic material can be single or double-stranded DNA or RNA.
This presentation gives a detail overview on Viruses - Morphology and Classification. The presentation is helpful for students of B. Pharm Second Year and those who wants to gain basic knowledge about Viruses.
Subject - Microbiology
Viruses range greatly in size and structure. They contain nucleic acid that is protected by a protein coat called a capsid. Some viruses have an additional lipid envelope surrounding the capsid that is acquired from the host cell. The capsid can have icosahedral or helical symmetry. Viruses require a living host cell to replicate and hijack the host's cellular machinery to produce new virus particles. Their structure allows them to infect host cells and their genetic material provides instructions to commandeer the host's resources for viral replication.
The document provides information about viruses including their structure, classification, life cycles, and how they cause disease. It begins by describing the characteristics of viruses and explaining that they are not living or nonliving but exhibit traits of both. It then discusses the discovery of viruses and describes the structures of representative viruses like bacteriophage, influenza, and HIV. The modes of viral classification including Baltimore classification are explained. The document also covers the parasitic nature of viruses and how they depend on host cells for replication and survival. It describes the general steps in the viral life cycle including adsorption, penetration, replication, assembly and release. The lytic and lysogenic cycles of bacteriophages are explained in detail.
Viruses are submicroscopic infectious agents that can only replicate inside living host cells. They contain either DNA or RNA as their genetic material but not both, unlike true living cells. Viruses exhibit both living properties like metabolism and heredity inside their host cells, as well as non-living properties like an inability to carry out metabolic activities independently. There are many types of viruses that infect different domains of life including plants, animals, bacteria and microorganisms. They have a variety of shapes and sizes and can be classified based on their genetic material, structure, and the cells they infect. Viruses cause diseases by hijacking host cell machinery to replicate and spread to other hosts.
VIRUSES CLASSIFICATION , LIFE CYCLE OF VIRUSES. CHARACTERISTICS OF VIRUSES Shylesh M
VIRUSES
LIFE CYCLE OF BACTERIOPHAGES
The word virus is derived from Latin word venom which means poisonous fluid that causes infection.
The branch of science that deals with the study of viruses is called Virology. It is the branch of Microbiology.
They show living characters inside the host and non living characters outside the host.
They contain either DNA or RNA as genetic material.
They have different size and shape. They cause diseases in plants, animals and micro-organisms .
Not cellular
Cannot carry on metabolic activities independently.
Contain either DNA or RNA, not both ( true cells contain both ).
Lack ribosomes and enzymes necessary for protein synthesis.
Reproduce only within cells they infect.
CLASSIFICATION OF VIRUSES
Holmes, in 1948, proposed a simple system of classifying viruses based on the type of cell (host) they infect:
Phytophagineae: They infect plants and they RNA as their genetic material. Eg: TMV,CaMV.
Zoophagineae: They infect animals and they have mostly DNA as their genetic material. Eg: Polio virus.
Pagineae: They infect bacterial cells, called bacteriophages they usually have DNA as genetic material.
Based on the viral envelope
Named after David Baltimore, a noble prize winning biologist n 1971.
1. dsDNA viruses Eg: Adenoviruses, Herpiviruses.
2. ssDNA viruses Eg: Paravoviruses.
3. dsRNA viruses Eg: Reoviruses.
4. (+)ssRNA viruses Eg: Picornaviruses.
5. (-)ssRNA viruses Eg: Orthomyxoviruses.
6. ssRNA-RT viruses Eg: Retroviruses.
7. dsDNA-RT viruses Eg: Hepadnaviruses.
Tobacco mosaic:
Causative agent: Tobacco mosaic virus (TMV)
Symptoms: The leaves of infected plants develop mosaic patches ,it is due to destruction of chlorophyll or due to production of abnormal chlorophyll .blisters appear in the region of dark green spots these may be regular or irregular in advanced stages leaves curl and get distorted.
Adsorption of the virion to the bacterial cell.
Penetration and decoating of the nucleic acid .
Protein synthesis.
Breakdown of bacterial DNA.
Arrest of host cell development.
Replication of phage DNA.
Maturation of infective progeny.
Lysis and release of newly formed phages.
Holmes, in 1948, proposed a simple system of classifying viruses based on the type of cell (host) they infect:
Phytophagineae: They infect plants and they RNA as their genetic material. Eg: TMV,CaMV.
Zoophagineae: They infect animals and they have mostly DNA as their genetic material. Eg: Polio virus.
Pagineae: They infect bacterial cells, called bacteriophages they usually have DNA as genetic material.
Early embryonic development involves a series of key stages:
1. Cleavage - The fertilized egg undergoes rapid, synchronized cell divisions without growth to form a solid ball of cells called a morula.
2. Blastulation - Cell divisions continue and a fluid-filled cavity called a blastocoel forms, establishing polarity and transforming the morula into a hollow ball of cells called a blastula.
3. Gastrulation - Cells migrate and rearrange through morphogenetic movements to form the three primary germ layers - ectoderm, endoderm, and mesoderm - establishing the body plan of the embryo.
This document discusses micropropagation as a method of clonally propagating plants. It begins by explaining traditional clonal propagation methods and their limitations. It then describes the benefits of micropropagation, which allows for rapid multiplication of plants using small explant tissues in sterile conditions. The document outlines the five main stages of micropropagation: preparation, initiation of cultures, multiplication, rooting, and transplantation. It provides details on each stage, focusing on choices of explants, factors influencing successful culture initiation, and methods of multiplication like regeneration from callus or direct shoot formation. Micropropagation offers advantages like high multiplication rates, disease elimination, and cryopreservation of plant materials.
Selection of plant species
Selection of mother plant for collection of explant
Explant
Surface sterilization
Media composition for various objectives (Callus, somatic embryo, shoot etc)
Genetic fidelity
Acclimatization (Primary hardening, secondary hardening, field transfer)
Developmental biology is the study of how organisms grow and develop. It involves processes like gametogenesis, fertilization, growth, differentiation, pattern formation and morphogenesis. Gametogenesis refers to the formation of gametes or sex cells through meiosis. In spermatogenesis, spermatogonia undergo mitosis and meiosis to form spermatids that then differentiate into spermatozoa. In oogenesis, oogonia undergo mitosis and meiosis to form a secondary oocyte and first polar body, with the secondary oocyte then undergoing a second meiotic division. Fertilization occurs when a sperm fuses with an ovum, forming a zygote. Development then progresses through
Translation is the process by which the genetic code stored in mRNA is used to synthesize proteins. It occurs on ribosomes using transfer RNA (tRNA) molecules to add amino acids to a growing polypeptide chain. There are three sites on the ribosome - the A site binds incoming tRNA, the P site holds tRNA with the polypeptide chain, and the E site releases tRNA. Through the repetitive binding of tRNA to mRNA codons and formation of peptide bonds, proteins specified by the mRNA are assembled from amino acids based on the genetic code.
This document describes the infrastructure, instruments, chemicals, and components needed for a plant tissue culture laboratory. It outlines the facilities and rooms required, including washing, media preparation, storage, inoculation, and growth rooms. It also lists the equipment, such as laminar flow cabinets, autoclaves, balances, pH meters, and plant growth chambers. Details are provided on types of glassware, media ingredients like macronutrients and nitrogen sources, and surface sterilization chemicals like carbendazim and mancozeb. The functions and formulation of plant tissue culture media are explained.
Unit 2 plant tissue culture applications, advantages and limitationsDr. Mafatlal Kher
This presentation is related to the application of plant tissue culture techniques in various sectors, and it also highlights the advantages and limitations of plant tissue culture
This document discusses micropropagation of banana (G-9) for commercial cultivation. It begins by outlining the nutritional value and various products of bananas. Next, it describes the limitations of traditional propagation methods using root suckers and advantages of micropropagation using tissue culture, which allows for large-scale, disease-free propagation. The document then details the specific micropropagation method used, including establishment of primary culture, shoot multiplication, rooting, and hardening/acclimatization. Finally, it proposes cost-effective solutions for some materials used, such as LED lights, table sugar, agar-agar type-II, RO water, and cocopeat. The overall aim is sustainable development of a banana industry through efficient
This document discusses bamboo tissue culture and the cultivation of bamboo. It begins with an overview of why tissue culture is used for plant propagation. It then discusses some of the limitations of traditional vegetative propagation and seed germination methods for bamboo, including disease transmission and limited plant production. The document notes that tissue culture allows for more efficient mass propagation of disease-free bamboo plants compared to traditional methods.
Unit 3.0 introduction and history of plant tissue cultureDr. Mafatlal Kher
Plant tissue culture is the process of growing plant cells, tissues or organs in an artificial nutrient medium under sterile conditions. The document discusses the history and development of plant tissue culture techniques. It notes that plant tissue culture is founded on cell theory proposed by Schleiden and Schwann in 1838-1839. Gottlieb Haberlandt is considered the father of plant tissue culture for his pioneering experiments in 1902, though his experiments failed due to inappropriate plant material and nutrient medium. Improved nutrient solutions like Knop's solution, White's medium and Murashige and Skoog medium enabled indefinite growth and multiplication of plant tissues in culture.
Unit 2 plant tissue culture lab ms media preparationDr. Mafatlal Kher
1. The document describes the preparation of MS medium from stock solutions for plant tissue culture. It provides the components and concentrations needed to make stock solutions A through D that contain macroelements, microelements, iron, and vitamins respectively.
2. The method explains how to make 1 L of working MS medium by combining the appropriate amounts of stock solutions A through D according to tables provided, and adding sucrose, inositol, and water. The medium is then distributed into flasks with different plant growth regulators as needed.
3. The medium is adjusted to pH 5.8, solidified with agar, and autoclaved before being distributed to culture vessels.
This presentation was provided by Steph Pollock of The American Psychological Association’s Journals Program, and Damita Snow, of The American Society of Civil Engineers (ASCE), for the initial session of NISO's 2024 Training Series "DEIA in the Scholarly Landscape." Session One: 'Setting Expectations: a DEIA Primer,' was held June 6, 2024.
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
The simplified electron and muon model, Oscillating Spacetime: The Foundation...RitikBhardwaj56
Discover the Simplified Electron and Muon Model: A New Wave-Based Approach to Understanding Particles delves into a groundbreaking theory that presents electrons and muons as rotating soliton waves within oscillating spacetime. Geared towards students, researchers, and science buffs, this book breaks down complex ideas into simple explanations. It covers topics such as electron waves, temporal dynamics, and the implications of this model on particle physics. With clear illustrations and easy-to-follow explanations, readers will gain a new outlook on the universe's fundamental nature.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
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Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
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Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
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This presentation includes basic of PCOS their pathology and treatment and also Ayurveda correlation of PCOS and Ayurvedic line of treatment mentioned in classics.
Thinking of getting a dog? Be aware that breeds like Pit Bulls, Rottweilers, and German Shepherds can be loyal and dangerous. Proper training and socialization are crucial to preventing aggressive behaviors. Ensure safety by understanding their needs and always supervising interactions. Stay safe, and enjoy your furry friends!
Strategies for Effective Upskilling is a presentation by Chinwendu Peace in a Your Skill Boost Masterclass organisation by the Excellence Foundation for South Sudan on 08th and 09th June 2024 from 1 PM to 3 PM on each day.
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
Introduction to AI for Nonprofits with Tapp Network
Unit 1 virology
1. By – Dr. Mafatlal M. Kher
Unit 1: Nature and Properties of Viruses
Date & Time : Monday, 27 September 2021
Semester : V
Program : B.Sc. Biotechnology
School : School of Science
Subject code : BSBO502 (Unit I)
1
9. Koch’s postulates
The agent must be present in every case of the disease.
The agent must be isolated from the host and grown in vitro.
The disease must be reproduced when a pure culture of the agent is inoculated
into a healthy susceptible host.
The same agent must be recovered once again from the experimentally infected
host.
9
11. Discovery of the first virus?
In 1892, Dmitri Ivanovsky to show that sap from a
diseased tobacco plant remained infectious to
healthy tobacco plants despite having been
filtered.
Martinus Beijerinck called the filtered, infectious
substance a "virus" and this discovery is
considered to be the beginning of virology.
11
Dmitri Ivanovsky
12. DEFINITION OF VIRUSES
Viruses are submicroscopic, obligate intracellular parasites. Most are too small to
be seen by optical microscopes, and they have no choice but to replicate inside
host cells.
12
13. DEFINITION OF VIRUSES
How viruses are UNIQUE?
Virus particles are produced from the assembly of preformed components, while
other biological agents grow from an increase in the integrated sum of their
components and reproduce by division.
Virus particles (virions) do not grow or undergo division.
Viruses lack the genetic information that encodes the tools necessary for the
generation of metabolic energy or for protein synthesis (ribosomes).
13
14. THE NATURE OF VIRUSES
14
Virus particles contain:
A nucleic acid genome (either DNA or RNA).
A protein coat (capsid) that encloses the
genome.
In some cases, a lipid membrane (envelope)
15. THE NATURE OF VIRUSES
Enveloped and non-enveloped viruses.
Enveloped viruses: Which have a lipid membrane (envelope) that is derived from
the host cell; and
Non-enveloped viruses, which lack a lipid membrane.
15
18. THE NATURE OF VIRUSES
The infectious virus particle is called a virion.
Virus particles are very small: between 20 and 500 nanometers (nm) in
diameter.
Viruses are obligatory intracellular parasites. (Only demonstrate life inside the
host cell).
Viruses multiply inside cells by expressing and replicating their genomes.
18
19. THE NATURE OF VIRUSES
Viruses need the following machinery provided by cells:
Enzyme systems that synthesize amino acids, nucleotides, carbohydrates, and
lipids.
Enzyme systems that generate useable chemical energy in the form of ATP.
Ribosomes, tRNAs, and enzymes used in protein synthesis.
Membranes that concentrate cellular macromolecules, small molecules, and ions.
19
20. THE NATURE OF VIRUSES
Viruses consist of a nucleic acid
genome packaged in a protein coat.
Viruses are the smallest and simplest
forms of life on Earth.
They consist of a set of nucleic acid
genes enclosed in a protein coat,
called a capsid, which in some cases
is surrounded by or encloses a lipid
membrane, called an envelope.
The viral genome encodes proteins
that enable it to replicate and to be
transmitted from one cell to another,
and from one organism to another.
The complete, infectious virus particle
is called a virion.
20
Figure: Schematic diagram of virus particles. Illustrated
are the two most common capsid morphologies: a roughly
spherical shell (left) and a tubular rod (right). Some virus
particles have an envelope (left) and some do not (right).
Nucleic acid genomes are shown as black curved lines,
capsid proteins as green spheres, and envelope proteins
as orange knobbed spikes. Source: Acheson (2011)
21. THE NATURE OF VIRUSES
Viruses are dependent on living cells for their replication
Viruses can replicate only within living cells because they are obligatory
intracellular parasites.
21
22. THE NATURE OF VIRUSES
Viruses are dependent on living cells for their REPLICATION: Viruses depend on
cells for their replication because they lack the following basic elements required for
growth and replication, which are present in all living cells:
Enzyme systems that produce the basic chemical building blocks of life:
nucleotides, amino acids, carbohydrates, and lipids.
Enzyme systems that generate useable chemical energy, usually in the form of
adenosine triphosphate (ATP), by photosynthesis or by metabolism of sugars and
other small molecules.
Ribosomes, transfer RNAs, and the associated enzymatic machinery that directs
protein synthesis.
Membranes that localize and concentrate in a defined space these cellular
macromolecules, the small organic molecules involved in growth and metabolism,
and specific inorganic ions.
22
23. VIRUS REPLICATION
The virion binds to cell surface receptors.
The virion or viral genome enters the cell;
the viral genome is uncoated.
Early viral genes are expressed.
Early viral proteins direct replication of the
viral genome.
Late viral genes are expressed from newly
replicated viral genomes.
Late viral proteins package genomes and
assemble progeny virus particles.
Virions are released from the host cell
23
24. THE NATURE OF VIRUSES
Virus particles breakdown and release their genomes inside the cell
Viruses are not the only obligatory intracellular parasites known.
A number of small unicellular organisms including chlamydiae and rickettsiae,
certain other bacterial species, and some protozoa can multiply only inside other
host cells.
24
25. THE NATURE OF VIRUSES
Virus particles break down and release their genomes inside the cell.
Viruses replicate by a pathway that is very different from the mode of
replication of other intracellular parasites:
Virus replication begins with at least partial disintegration of the virus particle, and
release (uncoating) of the viral genome within the cell.
Once uncoated, the viral genome can be used as a template for synthesis of
messenger RNAs, which in turn synthesize viral proteins using the enzyme
systems, energy, ribosomes, and molecular building blocks that are present in the
cell.
These viral proteins then direct replication of the viral genome.
Viral structural proteins encapsidate the newly replicated genomes to form
progeny virus particles.
25
26. THE NATURE OF VIRUSES
Virus particles break down and release their genomes inside the cell.
Multiplication of other intracellular parasites in host cell:
Unicellular organisms that replicate inside other cells invariably remain intact and
retain their genomes within their own cellular membranes.
They replicate not by disintegration and reassembly, but by growth and division
into daughter cells.
Such cellular parasites always contain their own ribosomes and protein synthetic
machinery, and their genes code for enzymes that direct many of the basic
metabolic pathways.
26
27. THE NATURE OF VIRUSES
Virus genomes are either RNA or DNA, but not both
All viruses contain genomes made of one and only one type of nucleic acid.
The smallest known viruses are 20 nanometers1 (nm) in diameter; their genomes
contain fewer than 2000 nucleotides, and they code for as few as 2 proteins. The
largest known viruses are some 500 nm in diameter; their genomes are as large
as 1.2 million nucleotides, and they code for over 1200 proteins.
Depending on the virus, the genome can be either RNA or DNA, and it can be
either single-stranded or double-stranded.
Some viral genomes are circular and others are linear
27
28. THE NATURE OF VIRUSES
Virus genomes are either RNA or DNA, but not both
Viruses are the only known forms of life that can have genomes made of RNA.
All cellular organisms store the information required to sustain life, to grow, and to
reproduce exclusively in DNA molecules, and all RNA molecules in these
organisms are transcribed from DNA sequences.
RNA-containing viruses are therefore unique, and they face two related
problems as a result of their RNA genomes:
They must synthesize messenger RNAs from an RNA template, and
They must replicate their genome RNA.
Most RNA viruses encode their own RNA-dependent RNA polymerases to
completed both these functions.
28
29. WHY STUDY VIRUSES?
Viruses are important disease-causing agents.
Probably all different forms of life can be infected by viruses.
Viruses can transfer genes between organisms.
Viruses are important players in the regulation of the Earth’s ecology.
Viruses can be engineered to prevent and cure disease.
Study of viruses reveals basic mechanisms of gene expression, cell physiology,
and intracellular signaling pathways.
29
30. WHY STUDY VIRUSES?
Smallpox, influenza, yellow fever,
COVID-19 and AIDS (acquired
immunodeficiency syndrome).
Viruses are responsible for many
cases of human encephalitis,
meningitis, pneumonia, hepatitis,
and cervical cancer, as well as warts
and the common cold.
Viruses causing respiratory
infections, gastroenteritis, and
diarrhea in young children lead to
millions of deaths each year in less-
developed countries
30
Viruses are important disease-causing agents
31. WHY STUDY VIRUSES?
Viruses can infect all forms of life
Viruses also infect animals, plants, and insects.
Outbreaks of virus diseases in domesticated animals can lead to destruction of
thousands or millions of animals to avoid even more widespread epidemics.
These diseases include avian influenza; foot-and-mouth disease of cattle;
infectious gastroenteritis and bronchitis in pigs, cattle, and chickens; sheep lung
tumors caused by a retrovirus; canine distemper; and feline immunodeficiency
disease.
Virus diseases affecting domesticated plants such as potatoes, tomatoes, tobacco,
coconut trees, and citrus trees are common and widespread.
Insect viruses that kill silkworms, used for centuries in Asia and Europe to produce
silk, have plagued that industry over the ages.
Viruses can also infect and kill bacteria, archaea, algae, fungi, and protozoa. 31
32. WHY STUDY VIRUSES?
Viruses are the most abundant form of life on Earth
Recent studies of soil and seawater have revealed
that bacterial viruses, also called bacteriophages, are
much more numerous than previously imagined.
There are 10–50 million bacteriophages on average
per mL of seawater, and even more in many soils.
Given the enormous volume of the oceans, scientists
have calculated that there may be as many as 1031
bacteriophages in the world.
This is about 10-fold greater than the estimated
number of bacteria. In terms of mass, this many
phages would weigh about 100 million tons, or the
equivalent of 1 million blue whales (the largest animal
on Earth).
More astonishing, these 1031 phages, if lined up
head-to-tail, would stretch some 200 million light
years into space—that is, far into the universe
beyond many of our known neighboring galaxies. 32
Scientists estimate that there are approximately 1031
tailed bacteriophages on Earth. Each phage
measures approximately 200 nm (0.2 µm) in length
from top of head to base of tail. Aligned head to tail,
these phages would therefore cover the following
distance:
1031 × 0.2 µm = 0.2 × 1025 meters = 2 × 1024 meters
= 2 × 1021 kilometers.
Because 1 light year (the distance travelled by light
in one year) =1013 kilometers,
2 × 1021 kilometers = 2 × 1021 /1013 light years
= 2 × 108 light years (200 million light years).
Note that our Milky Way galaxy measures
approximately 100,000 light years edge to edge, and
the furthest visible galaxies in the universe are
approximately 10 billion (10 × 109) light years distant.
Phages lined up through the universe
33. WHY STUDY VIRUSES?
Role of virus in Ecology
More important is the ecological role played by bacteriophages and viruses that
infect unicellular eukaryotic organisms such as algae and cyanobacteria.
From 95 to 98% of the biomass in the oceans is microbial (the remaining 2–5%
being made up of all other forms of life, including fish, marine invertebrates,
marine mammals, birds, and plants), and roughly half of the oxygen in the Earth’s
atmosphere is generated by photosynthetic activity of marine microbes.
It has been estimated that 20% of the microbes in the Earth’s oceans are
destroyed each day by virus infections.
Therefore, these viruses play a major role in the carbon and oxygen cycles that
regulate our atmosphere and help feed the world’s population.
33
34. WHY STUDY VIRUSES?
Role of virus in Ecology
More important is the ecological role played by bacteriophages and viruses that
infect unicellular eukaryotic organisms such as algae and cyanobacteria.
From 95 to 98% of the biomass in the oceans is microbial (the remaining 2–5%
being made up of all other forms of life, including fish, marine invertebrates,
marine mammals, birds, and plants), and roughly half of the oxygen in the Earth’s
atmosphere is generated by photosynthetic activity of marine microbes.
It has been estimated that 20% of the microbes in the Earth’s oceans are
destroyed each day by virus infections.
Therefore, these viruses play a major role in the carbon and oxygen cycles that
regulate our atmosphere and help feed the world’s population.
34
35. WHY STUDY VIRUSES?
Some viruses are useful
Sources of enzymes. A number of enzymes used in molecular biology are virus enzymes.
Examples include reverse transcriptases from retroviruses and RNA polymerases from
phages.
Pesticides. Some insect pests are control led with baculoviruses, and myxoma virus has
been used to control rabbits.
Anti-bacterial agents. In the mid-twentieth century phages were used to treat some
bacterial infections in humans. Interest waned with the discovery of antibiotics, but has
been renewed with the emergence of anti biotic-resistant strains of bacteria.
Anti-cancer agents. Genetically modified strains of viruses, such as herpes simplex virus
and vaccinia virus, are being investigated for treatment of cancers. These strains have
been modified so that they are able to infect and destroy specific tumor cells, but are
unable to infect normal cells.
Gene vectors for protein production. Viruses, such as certain baculoviruses and
adenoviruses, are used as vectors to take genes into an i mal cells growing in culture.
This technology is used to make cells produce useful proteins, such as vaccine
components. Some genetically modified cells are used for mass production of proteins
35
36. WHY STUDY VIRUSES?
The study of viruses has led to numerous discoveries in molecular and cell
biology
Because viruses replicate within cells but express a limited number of viral genes,
they are ideal tools for understanding the biology of cellular processes.
Research on animal, insect, and plant viruses has shed light on the functioning of
these organisms, their diseases, and molecular mechanisms of replication, cell
division, and signaling pathways.
The intensive study of bacteriophages led to discovery of some of the
fundamental principles of molecular biology and genetics.
36
37. WHY STUDY VIRUSES?
The study of viruses has led to numerous discoveries in molecular and cell
biology: Common examples
Study of gene expression in small DNA viruses led to the identification of
promoters for eukaryotic RNA polymerases.
Research on the replication of bacteriophage and animal virus DNAs laid the
foundations for understanding the enzymes involved in cellular DNA replication.
RNA splicing in eukaryotic cells was first discovered by studying messenger RNAs
of DNA viruses.
Study of cancer-producing viruses led to the isolation of numerous cellular
oncogenes and the understanding that cancer is caused by their mutation or
unregulated expression.
37
38. WHY STUDY VIRUSES?
The study of viruses has led to numerous discoveries in molecular and cell
biology: Common examples
A famous experiment carried by Alfred Hershey and Martha Chase, and published
in 1952, used phage T2 and E. coli to provi1de strong1 evidence that genetic
material is composed of DNA.
The first enhancers to be characterized were in genes of simian virus 40 (SV40).
Introns were discovered during studies of adenovirus transcription.
The first internal ribosome entry site to be discovered was found in the RNA of
poliovirus
38
39. WHY STUDY VIRUSES?: Case studies
Evidence that DNA is the genetic material of bacteriophage T2. The Hershey-
Chase experiment
Bacteriophage T2 was grown in E. coli in the presence of 35S (as sulphate) to label
the protein moiety, or 32P (as phosphate) to mainly label the nucleic acid. Purified,
labelled phages were allowed to attach to sensitive host cells and then given time
for the infection to commence.
The phages, still on the outside of the cell, were then subjected to the shearing
forces of a Waring blender.Such treatment removes any phage components
attached to the outside of the cell but does not affect cell viability. Moreover, the
cells are still able to produce infectious progeny virus.
When the cells were separated from the medium, it was observed that 75% of the
35S (i.e. phage protein) had been removed from the cells by blending but only 15%
of the 32P (i.e. phage nucleic acid) had been removed. Thus, after infection, the
bulk of the phage protein appeared to have no further function and this suggested
(but does not prove – that had to await more rigorous experiments with purified
nucleic acid genomes) that the nucleic acid is the carrier of viral heredity.
The transfer of the phage nucleic acid from its protein coat to the bacterial cell upon
infection also accounts for the existence of the eclipse period during the early
stages of intracellular virus development, since the nucleic acid on its own cannot
normally infect a cell.
39
Source: Dimmock et al. (2017)
40. WHY STUDY VIRUSES?: Case studies
The experiment of Fraenkel-Conrat and Singer which proved that RNA is the
genetic material of tobacco mosaic virus
Conrat and Singer (1957) were able to confirm by a different means the hereditary
role of viral RNA.
Their experiment was based on the earlier discovery that particles of tobacco
mosaic virus can be dissociated into their protein and RNA components, and then
reassembled to give particles which are morphologically mature and fully infectious.
When particles of two different strains (differing in the symptoms produced in the
host plant) were each disassociated and the RNA of one reassociated with the
protein of the other, and vice versa, the properties of the virus which was
propagated when the resulting ‘hybrid’ particles were used to infect host plants were
always those of the parent virus from which the RNA was derived.
The ultimate proof that viral nucleic acid is the genetic material came from
numerous observations that, under special circumstances, purified viral nucleic acid
is capable of initiating infection, albeit with a reduced efficiency. For example, in
1956 Gierer and Schramm, and Fraenkel-Conrat independently showed that the
purified RNA of tobacco mosaic virus can be infectious, provided precautions are
taken to protect it from inactivation by ribonuclease. An extreme example is the
causative agent of potato spindle tuber disease which lacks any protein component
and consists solely of RNA. Because such agents have no protein coat, they cannot
be called viruses and are referred to as viroids
40
Source: Dimmock et al. (2017)
41. THEORIES OF VIRAL ORIGIN
The regressive, or reduction or Degenerate cells hypothesis
Just as fleas are descended from flies by loss of wings, viruses may be derived
from pro- or eukaryotic cells that have dispensed with many of their cellular
functions (degeneracy).
Viruses began as small cells that, much like bacteria such as Chlamydia, infect
larger cells. These pre-virus cells then lost their metabolic and most of their
reproductive abilities, and became inert outside of a cellular environment, and
reliant on cellular pathways for reproduction.
41
42. THEORIES OF VIRAL ORIGIN
The escape, or cellular, hypothesis
Mobile elements such as retrotransposons obtained genes encoding capsid
proteins and enzymes, and, much like plasmids we know today, were able to
escape from their original cellular environment and move to, and replicate in, other
cells.
Alternatively, some nucleic acid might have been transferred accidentally into a
cell of a different species (e.g. through a wound or by sexual contact) and, instead
of being degraded as would normally be the case, might have survived and
replicated (escape).
42
43. THEORIES OF VIRAL ORIGIN
Co-evolution, or virus-first, hypothesis
Both cells and viruses evolved alongside each other.
The co-evolution hypothesis predicts that viruses for the three domains of life –
Archaea, Bacteria, and Eucaryota – would have some genetic similarity to their
hosts, and differ from viruses infecting other.
43
44. THEORIES OF VIRAL ORIGIN
Despite decades of discussion and argument there are no firm indications if either,
or of these theories are correct.
Rapid sequencing of viral and cellular genomes is now providing data for computer
analysis that are giving an ever-better understanding of the relatedness of different
viruses.
However, while such analyses may identify, or more commonly infer, the
progenitors of a virus, they cannot decide between degeneracy, escape or co-
evolution.
It is unlikely that all currently-known viruses have evolved from a single progenitor.
Rather, viruses have probably arisen numerous times in the past by any of the
mechanisms discussed so far.
44
46. Viroids
Viroids are infectious agents that consist only of RNA.
They cause over 20 different plant diseases, including potato spindle-tuber
disease, exocortis disease of citrus trees, and chrysanthemum stunt disease.
Viroids are covalently closed, circular ssRNAs, about 250 to 370 nucleotides long.
The RNA of viroids does not encode any gene products, so they cannot replicate
themselves.
Viroid is replicated by a host cell enzyme called a DNA-dependent RNA
polymerase.
This enzyme normally functions in the host to synthesize RNA using DNA as the
template during transcription.
However, when infected by a viroid, the host polymerase evidently uses the viroid
RNA as a template for RNA synthesis, rather than its own DNA.
The host polymerase synthesizes a complementary RNA molecule, which then
serves as the template for synthesis of new viroid RNAs.
46
47. Satellite viruses/virusoids
Virusoids possess linear or circular RNA
as genetic material.
Virusoids can not replicate
autonomously they require the cells
infected with a virus that function as a
helper for replication.
47
48. Satellite viruses/virusoids
Satellites are similar to viroids in that they also consist only of a nucleic acid (either
DNA or RNA).
They differ from viroids in that they may encode one or more gene products and
need a helper virus to replicate and infect host cells.
There is no homology between the genome of the satellite and its helper virus.
Satellites are further divided into three types:
Satellite viruses,
Satellite RNAs, and
Satellite DNAs.
Satellite viruses encode their own capsid proteins, whereas satellite RNAs and
DNAs do not.
Most satellites use plant viruses as their helper viruses.
48
49. Prions
Prions (proteinaceous infectious particle:
misfolded protein which is infectious in
nature) cause a variety of neuro
degenerative diseases in humans and other
animals.
Prions are encoded by host chromosomes.
Prion protein triggers normal protein to fold
abnormally which causes disease.
Scrapie in sheep, Bovine spongiform
encephalopathy (BSE or “mad cow disease”):
Cow and Humans. Human diseases kuru, fatal
familial insomnia, Creutzfeldt-Jakob disease
(CJD), and Gerstmann-Strassler-Scheinker
syndrome (GSS). All result in progressive
degeneration of the brain and eventual death.
At present, no effective treatment exists.
The best-studied prion is the scrapie prion.
Researchers have shown that scrapie is
caused by an abnormal form of a cellular
protein.The abnormal form is called PrPsc (for
scrapie-associated prion protein), and the
normal cellular form is called PrPc. 49
Reference: Wiley et al 2020 chapter 6
50. Viriods, Satellites and Prions
50
Viriod like sat RNA Linear sat RNA Viriods
Host Plants Plants Plants
Helper virus SNMV CMV None
Genome ssRNA ssRNA ssRNA
Replication HV Replicase HV Replicase Cellular polymerase
Site of replication Cytoplasm Nucleus/cytoplasm Nucleus
Coding capacity None None None
# Encapsidation HV CP (Helper virus coat
protein)
HV CP None
# Encapsidation: The enclosure of viral nucleic acid within a capsid.
51. Capsid symmetry
Capsid v/s nucleocapsid
At the molecular level, the outer shell of a virion can be a rigid, symmetrical
container called a capsid (derived from the Latin capsa ⫽ box).
Capsid consists of several oligomeric (repeating) structural subunits made of
protein called protomers.
The observable 3-dimensional morphological subunits, which may or may not
correspond to individual proteins, are called capsomeres.
The proteins making up the capsid are called capsid proteins or viral coat
proteins (VCP).
When the viral nucleic acid genome is packaged within the capsid, the resulting
structure is called a nucleocapsid.
51
53. Capsid symmetry
Symmetry refers to the way in which capsomere units are arranged in viral capsid.
Two kinds of symmetry are recognized in the viruses which corresponds to two
primary shape ie. Rod and spherical shape of virus.
Rod shaped virus have helical symmetry and spherical shaped virus have
icosahedral symmetry.
53
54. Capsid symmetry
Helical (spiral) symmetry
The capsomere and nucleic
acid are wined together to
form helical or spiral tube like
structure.
Most of the helical viruses are
enveloped and all are RNA
viruses.
The typical virus with helical
symmetry is tobacco mosaic
virus (TMV), which is a RNA
virus with 2130 identical
capsomeres arranged in a
helix. 54
55. Capsid symmetry
Icosahedral (cubical) symmetry
An icosahedral is a polygon with 12 vertices (corner), 20 facet (sides) and 30
edges.
Each facet is an equilateral triange.
Icosahedral capsid is the most stable and found in human pathogenic virus eg.
Adenovirus, Picornavirus, Papovavirus, herpes virus etc.
Icosahedral capsid are of two types;
Pentagon; Pentagonal capsomere at the vertices
Hexagon; Hexagonal capsomere at the vertices
55
56. Capsid symmetry
Complex symmetry
Some virus are more complex, being composed of several separate capsomere
with separate shape and symmetry.
They do not have either icosahedral or helical symmetry due to complexity of their
capsid structure. Eg. Pox virus, Bacteriophage.
Binal symmetry: it is a type of complex symmetry
Some viruses such as T-phage (T2,T4 etc) have compex symmetry including head
and tail
The most complicated virus in terms of structure are some bacteriophage which
possess icosahedral head and helical tail. Such structure is called binal symmetry.
56
57. Cultivation and purification of viruses
Viruses are obligate intracellular parasites so they depend on host for their
survival.
They cannot be grown in non-living culture media or on agar plates alone, they
must require living cells to support their replication.
57
58. Cultivation and purification of viruses
The diagnosis of viral diseases like the flu and a cold are usually straightforward
and do not require further laboratory confirmation.
In the classical sense, Koch’s postulates cannot be applied to a viral disease
because, unlike bacterial cells, viruses cannot be cultivated in pure culture.
58
59. Cultivation and purification of viruses
Rivers’ postulates
Thomas M. Rivers in 1937 expanded Koch’s postulates to include viruses.
He proposed filtrates of the infectious material isolated from the diseased host
shown not to contain bacterial or other cultivatable organisms must produce the
same disease as found in the original host; or, the filtrates must produce specific
antibodies in appropriate animals.
This concept has come to be known as Rivers’ postulates
59
60. Cultivation and purification of viruses
Virus require living cells as their medium
In vivo: Laboratory bred animals and embryonic bird tissues.
In Vitro: Cell or Tissue culture Methods
60
61. Cultivation and purification of viruses
The Objective of Virus cultivations:-
To isolate and identify viruses in clinical samples.
To do research on virus structure, replications, genetics, and effects on host cell.
To prepare viruses for vaccine production.
61
62. Cultivation and purification of viruses
The primary purpose of virus cultivation is:
To isolate and identify viruses in clinical samples.
To do research on viral structure, replication, genetics and effects on host cell.
To prepare viruses for vaccine production.
62
63. Cultivation and purification of viruses
Cultivation of viruses can be
discussed under following
headings:
Animal Inoculation
Inoculation into embryonated
egg
Cell Culture
63
64. Cultivation and purification of viruses
Animal Inoculation
Viruses which are not cultivated in embryonated egg and tissue culture are cultivated in
laboratory animals such as mice, guinea pig, hamster, rabbits and primates are used.
The selected animals should be healthy and free from any communicable diseases.
Suckling mice(less than 48 hours old) are most commonly used.
Suckling mice are susceptible to togavirus and coxsackie virues, which are inoculated by
intracerebral and intranasal route.
Viruses can also be inoculated by intraperitoneal and subcutaneous route.
After inoculation, virus multiply in host and develops disease. The animals are observed
for symptoms of disease and death.
Then the virus is isolated and purified from the tissue of these animals.
Live inoculation was first used on human volunteers for the study of yellow fever virus.
64
65. Cultivation and purification of viruses
Advantages of Animal Inoculation
Diagnosis, Pathogenesis and clinical symptoms are determined.
Production of antibodies can be identified.
Primary isolation of certain viruses.
Mice provide a reliable model for studying viral replication.
Used for the study of immune responses, epidemiology and oncogenesis.
65
66. Cultivation and purification of viruses
Limitations of Animal Inoculation
Expensive and difficulties in maintenance of animals.
Difficulty in choosing of animals for particular virus
Some human viruses cannot be grown in animals, or can be grown but do not
cause disease.
Mice do not provide models for vaccine development.
It will lead to generation of escape mutants
Issues related to animal welfare systems.
66
67. Cultivation and purification of viruses
Inoculation into embryonated egg
Good pasture in 1931 first used the embryonated hen’s egg for
the cultivation of virus.
The process of cultivation of viruses in embryonated eggs
depends on the type of egg which is used.
Viruses are inoculated into chick embryo of 7-12 days old.
For inoculation, eggs are first prepared for cultivation, the shell
surface is first disinfected with iodine and penetrated with a
small sterile drill.
After inoculation, the opening is sealed with gelatin or paraffin
and incubated at 36°c for 2-3 days.
After incubation, the egg is broken and virus is isolated from
tissue of egg.
Viral growth and multiplication in the egg embryo is indicated by
the death of the embryo, by embryo cell damage, or by the
formation of typical pocks or lesions on the egg membranes
Viruses can be cultivated in various parts of egg like
chorioallantoic membrane, allantoic cavity, amniotic sac and
yolk sac.
67
68. Cultivation and purification of viruses
Inoculation into embryonated egg
Chorioallantoic Membrane (CAM):
Inoculation is mainly for growing poxvirus.
After incubation and incubation, visible lesions called pocks are observed, which is
grey white area in transparent CAM.
Herpes simplex virus is also grown.
Single virus gives single pocks
This method is suitable for plaque studies.
68
69. Cultivation and purification of viruses
Inoculation into embryonated egg
Allantoic cavity:
Inoculation is mainly done for production of vaccine of influenza virus, yellow fever,
rabies.
Most of avian viruses can be isolated using this method.
69
70. Cultivation and purification of viruses
Inoculation into embryonated
egg
Amniotic sac:
Inoculation is mainly done for
primary isolation of influenza virus
and the mumps virus.
Growth and replication of virus in
egg embryo can be detected by
haemagglutination assay.
70
71. Cultivation and purification of viruses
Inoculation into embryonated egg
Yolk sac inoculation:
It is also a simplest method for growth and multiplication of virus.
It is inoculated for cultivation of some viruses and some bacteria (Chlamydia,
Rickettsiae)
Immune interference mechanism can be detected in most of avian viruses.
71
72. Cultivation and purification of viruses
Advantages of Inoculation into embryonated egg:
Widely used method for the isolation of virus and growth.
Ideal substrate for the viral growth and replication.
Isolation and cultivation of many avian and few mammalian viruses.
Cost effective and maintenance is much easier.
Less labor is needed.
The embryonated eggs are readily available.
Sterile and wide range of tissues and fluids
They are free from contaminating bacteria and many latent viruses.
Specific and non specific factors of defense are not involved in embryonated eggs.
Widely used method to grow virus for some vaccine production.
72
73. Cultivation and purification of viruses
Limitations of Inoculation into embryonated egg:
The site of inoculation for varies with different virus i.e. each virus have different
sites for their growth and replication.
73
74. Cultivation and purification of viruses
Tissue/cell Culture: There are three types of tissue culture; organ culture, explant
culture and cell culture.
Organ cultures are mainly done for highly specialized parasites of certain organs
e.g. tracheal ring culture is done for isolation of coronavirus.
Explant culture is rarely done.
Cell culture is mostly used for identification and cultivation of viruses.
74
75. Cultivation and purification of viruses
Cell culture is mostly used for identification and cultivation of viruses.
Cell culture is the process by which cells are grown under controlled conditions.
Cells are grown in vitro on glass or a treated plastic surface in a suitable growth
medium.
At first growth medium, usually balanced salt solution containing 13 amino acids,
sugar, proteins, salts, calf serum, buffer, antibiotics and phenol red are taken and
the host tissue or cell is inoculated.
On incubation the cell divide and spread out on the glass surface to form a
confluent monolayer.
75
76. Cultivation and purification of viruses
Types of cell culture.
Primary cell culture:
These are normal cells derived from animal or human cells.
They are able to grow only for limited time and cannot be maintained in serial
culture.
They are used for the primary isolation of viruses and production of vaccine.
Examples: Monkey kidney cell culture, Human amnion cell culture
76
77. Cultivation and purification of viruses
Types of cell culture.
Diploid cell culture (Semi-continuous cell lines):
They are diploid and contain the same number of chromosomes as the parent
cells.
They can be sub-cultured up to 50 times by serial transfer following senescence
and the cell strain is lost.
They are used for the isolation of some fastidious viruses and production of viral
vaccines.
Examples: Human embryonic lung strain, Rhesus embryo cell strain
77
78. Cultivation and purification of viruses
Types of cell culture.
Heteroploid cultures (Continuous cell lines):
They are derived from cancer cells.
They can be serially cultured indefinitely so named as continuous cell lines
They can be maintained either by serial subculture or by storing in deep freeze at -
70°c.
Due to derivation from cancer cells they are not useful for vaccine production.
Examples: HeLa (Human Carcinoma of cervix cell line), HEP-2 (Humman
Epithelioma of larynx cell line), Vero (Vervet monkey) kidney cell lines, BHK-21
(Baby Hamster Kidney cell line).
78
79. Cultivation and purification of viruses
Types of cell culture.
Susceptible Cell Lines:
Herpes Simplex Vero Hep-2, human
diploid (HEK and HEL),human amnion
VZV human diploid (HEL, HEK)
CMV human diploid fibroblasts
Adenovirus Hep2, HEK,
Poliovirus MK, BGM, LLC-MK2,
human diploid, Vero, Hep-
2,Rhadomyosarcoma
Coxsackie B MK, BGM, LLC-MK2,
vero, hep-2
Echo MK, BGM, LLC-MK2, human
diploid, Rd
Influenza A MK, LLC-MK2, MDCK
Influenza B MK, LLC-MK2, MDCK
Parainfluenza MK, LLC-MK2
Mumps MK, LLC-MK2, HEK, Vero
RSV Hep-2, Vero
Rhinovirus human diploid (HEK, HEL)
Measles MK, HEK
Rubella Vero, RK13
79
80. Cultivation and purification of viruses
Advantages of cell culture
Relative ease,
Broad spectrum,
Cheaper and
Sensitivity
80
81. Cultivation and purification of viruses
Limitations of cell culture
The process requires trained technicians with experience in working on a full time
basis.
State health laboratories and hospital laboratories do not isolate and identify
viruses in clinical work.
Tissue or serum for analysis is sent to central laboratories to identify virus.
81
82. Cultivation and purification of viruses
Cultivation of plant viruses
There are some methods of cultivation of plant viruses such as plant tissue
cultures, cultures of separated cells, or cultures of protoplasts, etc. viruses can be
grown in whole plants.
Leaves are mechanically inoculated by rubbing with a mixture of viruses and an
abrasive. When the cell wall is broken by the abrasive, the viruses directly contact
the plasma membrane and infect the exposed host cells.
A localized necrotic lesion often develops due to the rapid death of cells in the
infected area.
Some plant viruses can be transmitted only if a diseased part is grafted onto a
healthy plant.
82
83. Cultivation and purification of viruses
Cultivation of bacteriophages
Bacteriophages are cultivated in either broth or agar cultures of young, actively
growing bacterial cells.
83
84. Purification of Viruses
Ultracentrifugation
Ultracentrifugation is used to separate macromolecules into different component parts based on the size of the
particles in the mixture.
Different kinds of particles such as viruses, bacteria, and organelles have different sizes and will be driven away
from the centrifugal axis in the equipment to different locations accordingly. This is called velocity sedimentation.
A viscous liquid such as glycerol, sucrose, or cellufine sulfate, is used in the process to help control the rate of
migration of the different kinds of particles or else the rate of their migration away from the axis will be too fast. A
slower rate of migration helps to better purify the mixture.
An alternative form of centrifugation called isopycnic density can also be used , which separates molecules
based on their buoyancy density in the viscous fluid. The fluid has a greater density at the bottom than at the top.
When the mixture is centrifuged, the particles, including the virus molecules, migrate to the level of the liquid which
relates to their density. A combination of both velocity sedimentation and isopycnic density centrifugation can be a
particularly useful form of purification
84
85. Purification of Viruses
Chromatography
Chromatography is useful for purifying both enveloped and non-enveloped viruses. Most viruses are enveloped which
mean that they have their nucleic acid (DNA and RNA) covered in a protein cover called the capsid which further has a
membrane envelope on it.
Examples of enveloped viruses are the chickenpox virus and the influenza virus. Non-enveloped viruses do not have
the envelope. Examples of these non-enveloped viruses are parvovirus and adeno virus. Non-enveloped viruses are not
impacted by heat, drying or acids while enveloped viruses can be affected by these.
The level of purification varies from one virus to the next. Pore size has an impact on how much of the virus is removed
and so does the kind of resin, protein solution, and buffer.
It is also more difficult to remove smaller viruses fully with this method.
85
86. Purification of Plant Viruses
Purification refers to the separation of virus particles
from host components in a biologically active state.
Purified virus is required for the production of
antibodies, physical, biochemical and molecular
characterization of virus isolates.
Purification of virus involves several steps such as
propagation of the virus in the host, extraction of sap,
clarification, concentration and further purification.
Purity of purified preparation can be checked through
UV absorption spectra and its infectivity by
inoculating to a susceptible host under optimal
environmental conditions in an insect-proof
glasshouse. Purification methods vary with different
viruses, and there are no universal methods of virus
purification. Procedures that are effective for one
virus may not work with the other. Stable viruses that
reach high concentration in their propagation hosts
are easy to purify compared to viruses that are less
stable and occur in low concentration in their hosts. 86
87. Classification of viruses
Classification on the basis of disease
Classification on the basis of host organism
Classification on the basis of virus particle morphology
Classification on the basis of viral nucleic acids
Classification on the basis of taxonomy
Satellites, viroids and prions
87
88. References
Acheson NH (2011) Fundamentals of molecular virology (Second edition). Wiley-
Blackwell, Oxford, UK
Cann AJ (2016) Principles of molecular virology. Academic Press + Elsevier Inc
Carter J, Saunders V (2013) Virology: Principles and Applications (Second
edition). Wiley-Blackwell, Oxford, UK
Dimmock NJ, Easton AJ, Leppard KN (2017) Introduction to modern virology
(Seventh edition). Wiley-Blackwell, Oxford, UK
Korsman SNJ, Van Zyl GU, Nutt L, Andersson MI, Preiser W (2012) Virology: An
illustrated colour text. Churchill Livingstone Elsevier, Edinburgh, UK
Willey J, Sherwood L, Woolverton C (2020) Prescott’s Microbiology (Eleventh
edition): Chapter six, McGraw-Hill Education, New York, USA
88