Viruses are small obligate intracellular parasites, which by definition contain either an RNA or DNA genome surrounded by a protective, virus-coded protein coat. Viruses range from the structurally simple and small parvoviruses and picornaviruses to the large and complex poxviruses and herpesviruses. Viruses are classified on the basis of morphology, chemical composition, and mode of replication. The viruses that infect humans are currently grouped into 21 families, reflecting only a small part of the spectrum of the multitude of different viruses whose host ranges extend from vertebrates to protozoa and from plants and fungi to bacteria.
Virus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms.
Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. Currently, two main schemes are used for the classification of viruses: the International Committee on Taxonomy of Viruses (ICTV) system and Baltimore classification system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the ICTV.
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.
Virus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms.
Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. Currently, two main schemes are used for the classification of viruses: the International Committee on Taxonomy of Viruses (ICTV) system and Baltimore classification system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the ICTV.
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.
Structure and composition of plant virusesDivya Singh
Virus is chemically a nucleoprotein that multiplies only in the living cells and has ability to cause disease.
Nucleic acid may be RNA or DNA that is surrounded by a protective protein coat called capsid.
Plant viruses may be elongated, spherical and bacilliform in shape.
The nucleic acids RNA and DNA may be single stranded or double stranded.
Nucleic acid % is lower in elongated viruses where as spherical viruses contain higher % of nucleic acid.
viruses are intracellular obligate parasites. They are either DNA or RNA viruses. In order to grow in labs, tissue culture is used. Some general characteristics of viruses are discussed here.
Structure and composition of plant virusesDivya Singh
Virus is chemically a nucleoprotein that multiplies only in the living cells and has ability to cause disease.
Nucleic acid may be RNA or DNA that is surrounded by a protective protein coat called capsid.
Plant viruses may be elongated, spherical and bacilliform in shape.
The nucleic acids RNA and DNA may be single stranded or double stranded.
Nucleic acid % is lower in elongated viruses where as spherical viruses contain higher % of nucleic acid.
viruses are intracellular obligate parasites. They are either DNA or RNA viruses. In order to grow in labs, tissue culture is used. Some general characteristics of viruses are discussed here.
introduction to viruses, classification and structure.kanchan sharma
introduction to viruses. structure of viruses.
classification of viruses.
structure of plant, animal and bacterial viruses.
satellite virus, viroids, virions, their structure and function
examples of animal and plant viruses.
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Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat. Viruses range from the
structurally simple and small parvoviruses and picornaviruses to the large and complex
poxviruses and herpesviruses. Viruses are classified on the basis of morphology, chemical
composition, and mode of replication. The viruses that infect humans are currently grouped into 21 families, reflecting only a small part of the spectrum of the multitude of different viruses whose host ranges extend from vertebrates to protozoa and from plants and fungi to bacteria.
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The term ‘virus’ derives from the Latin – poison or Venom.• Viruses are much smaller than bacteria, use their genome (DNA or RNA) to replicate themselves in the host cells and synthesize viral particle.The viral structure mainly having following parts: Viral genome, Capsid, Some are enclosed by an envelope while Some viruses have spikes.• Viruses are classified on basis of their morphology, structure, Genome, presence of envelope, type of host, mode of transmission, replication site and Baltimore classification.
Viral replication by Kainat Ramzan-SlideShareKainatRamzan3
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The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
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2. Virus:
Viruses are small obligate intracellular parasites which contain either a RNA or
DNA.
Viruses are classified on the basis of morphology, chemical composition, and
mode of replication.
Virion morphology including size, shape, type of symmetry etc
Virus genome properties, including type of nucleic acid either DNA or RNA
Genome organization and replication.
Antigenic properties
Physicochemical properties of the virion including molecular mass etc
6. On the basis of genetic material
The nucleic acid may be single or double stranded, circular or linear, segmented or
unsegmented. They are classified as DNA viruses and RNA viruses
1. DNA viruses
• DNA as their genetic material.
• Example: parvovirus, papillomavirus, and herpesvirus
2. RNA viruses
DNA viruses cause human diseases, such as chickenpox, hepatitis B. They possess RNA as
genetic material
Single-stranded or double-stranded , positive-sense and negative-sense RNA viruses
These RNA polymerase enzymes are more likely to make copying errors than DNA
polymerases, and therefore often make mistakes during transcription
Human diseases caused by RNA viruses include hepatitis C, measles, and rabies
3.DNA-RNA viruses
The RNA tumor viruses called Leukoviruses and Rous’s viruses unusually contain both
DNA and RNA as genetic material
7. On the basis of presence of number of strands
Double-stranded DNA
It is found in pox viruses, the bacteriophages herpes viruses, adenoviruses etc.
Single-stranded DNA
It is found in bacteriophages.
Double-stranded RNA
It has been found within viral capsid in the reoviruses of animals and in the
wound tumour virus.
Single-stranded RNA
It is found in most of the RNA viruses
- tobacco mosaic virus, influenza virus etc.
8. On the basis of presence of envelope
1. Non – enveloped viruses
A non-enveloped animal virus that causes respiratory illnesses in humans,
uses glycoprotein spikes protruding from its capsomeres to attach to host
cells.
Adenovirus, poliovirus are example of it
2. Enveloped virus
Glycoproteins embedded in the viral envelope are used to attach to host
cells Chicken pox, influenza, and mumps are examples of diseases caused
by viruses with envelopes.
Because of the fragility of the envelope, non-enveloped viruses are more
resistant to changes in temperature, pH
9. On the basis of Capsid structure:
All virions have a nucleic acid genome covered by a protective layer of proteins called
a capsid
Capsid is the protein shell that encloses the nucleic acid with its enclosed nucleic acid
called as Nucleocapsid
Shell is composed of protein organized in subunits known as Capsomers
Protects the nucleic acid from digestion by enzymes,
Contains special sites on its surface that allow the virion to attach to a host cell,
Provides proteins that enable to penetrate the host cell membrane and to inject the
infectious nucleic acid into the cell's cytoplasm
Filamentous viruses are long and cylindrical
Many plant viruses are filamentous, including TMV
Isometric viruses have shapes that are roughly spherical,
- such as poliovirus or herpesviruses
Enveloped viruses have membranes surrounding capsid
- Animal viruses, such as HIV
10. Head and tail viruses infect bacteria and
- have a head ---similar to icosahedral viruses
- a tail shape like filamentous viruses
Complex with many Proteins: some have combinations of icosahedral and helical
capsid structures.
-Herpesviruses, smallpox virus,
- hepatitis B virus, T4 bacteriophage
11. On the Basis of Shapes of the Viruses
Rabies Lyssavirus commonly known as the Rabies virus (RABV)
Bullet-shaped, neurotropic virus
Composed of an internal protein core or nucleocapsid containing the nucleic acid,
and an outer envelope,
Lipid-containing bilayer covered with transmembrane glycoprotein spikes.
Negative-sense, non-segmented, single-stranded RNA virus and approximately 60
nm × 180 nm
Ebola Virus
Negative-sense, non-segmented, single stranded linear RNA genome about 18-19 kb
in size, contains approximately 19,000 base pairs
Nucleoprotein (NP), polymerase cofactor (VP35), (VP40), GP, transcription
activator (VP30), VP24, and RNA polymerase (L)
Cylindrical, tubular, and contain viral envelope, matrix and nucleocapsid components
12. Poxviruses
Brick-shaped (240 nm by 300 nm) and have a complex internal structure
Double-stranded DNA genome (130–260 kb) and associated enzymes
Adenoviruses
Medium-sized (90-100 nm),
non-enveloped icosohedral viruses with double-stranded DNA
The shell, which is 70 to 100 nm in diameter, is made up of
252 structural capsomeres
Adenovirus is Space vehicle shaped
13. Classification of Virus on the Basis of Structure
Cubical virus:
They are also known as icosahedral symmetry virus.
Polygon with 12 vertices (corner), 20 facet (sides) and 30 edges
E.g; Adenovirus, Picornavirus, Papovavirus, herpes virus
Spiral virus:
They are also known as helical symmetry virus
The capsomere and nucleic acid are wined together to form helical or spiral tube
like structure
Helical viruses are enveloped and all are RNA viruses with 2130 identical
capsomeres
E.g; Paramyxovirus, orthomyxovirus
Radial symmetry virus is Bacteriophage virus
Complex virus like Pox virus
14. On the basis of type of host
Animal Viruses
Viruses which infect and live inside the animal cell
Influenza virus, mumps virus, poliovirus
Genetic material --- RNA or DNA
Plant Viruses
The viruses that infect plants
Genetic material is RNA
- remains enclosed in the protein coat
Tobacco mosaic virus, potato virus, beet yellow virus
Bacteriophages
Viruses which infect bacterial cells
DNA as genetic material
Each kind of bacteriophage will attack only single specie
15.
16. On the basis of mode of transmission
Virus transmitted through respiratory route
- Swine flu, Rhino virus
Virus transmitted through fecal oral route
- Hepatitis A virus, Polio virus, Rota virus
Virus also transmitted through blood transfusion
- Hepatitis B virus, HIV
Zoonotic virus which transmitted through biting of infected animals
- Rabies virus, Alpha virus
17. On the Basis of Replication Properties and Site of
Replication
All RNA virus replicate and assemble in cytoplasm of host cell except
Influenza virus
Some virus Replicate in nucleus and assemble in cytoplasm of host like
Influenza virus, Pox virus
Some Replicate and assemble in nucleus of host like All DNA viruses
replicate and assemble in nucleus of host cell except Pox virus.
Virus also replicate through double stranded DNA intermediate like all DNA
virus, and some tumor causing RNA virus replicates through dsDNA.
Some Virus replicate through single stranded RNA intermediate like All RNA
virus except Reo virus and tumor causing RNA viruses
18. Baltimore classification
The most commonly used system of virus classification was developed by Nobel Prize-
winning biologist David Baltimore in the early 1970s.
The Baltimore classification scheme groups viruses according to how the mRNA is
produced during the replicative cycle of the virus
The most commonly used classification method today is called the Baltimore
classification scheme and is based on how messenger RNA (mRNA) is generated in each
particular type of virus
Group I
viruses contain double-stranded DNA (dsDNA) as their genome.
Their mRNA is produced by transcription in much the same way as with cellular DNA
Group II
viruses have single-stranded DNA (ssDNA) as their genome.
They convert their single-stranded genomes into a dsDNA intermediate before
transcription to mRNA can occur
19. Group III
viruses use dsRNA as their genome. The strands separate, and one of them is
used as a template for the generation of mRNA using the RNA-dependent RNA
polymerase encoded by the virus
Group IV
Viruses have ssRNA as their genome with a positive polarity. Positive
polarity means that the genomic RNA can serve directly as mRNA.
Intermediates of dsRNA, called replicative intermediates, are made in the
process of copying the genomic RNA
Group V
Viruses contain ssRNA genomes with a negative polarity, meaning that their
sequence is complementary to the mRNA. In this case, the negative-stranded
genome can be converted directly to mRNA.
Additionally, full-length positive RNA strands are made to serve as templates for
the production of the negative-stranded genome
20. Group VI
Viruses have diploid (two copies) ssRNA genomes that must be converted,
using the enzyme reverse transcriptase, to dsDNA; the dsDNA is then
transported to the nucleus of the host cell and inserted into the host genome.
Then, mRNA can be produced by transcription of the viral DNA that was
integrated into the host genome
Group VII
Viruses have partial dsDNA genomes and make ssRNA intermediates that act
as mRNA, but are also converted back into dsDNA genomes by reverse
transcriptase, necessary for genome replication.
