SlideShare a Scribd company logo

Viruses SMG

A general account of viruses

1 of 76
Download to read offline
VIRUSES
Dr Saji Mariam George
Associate Professor
Assumption College Autonomous
Changanacherry.
VIRUSES
• The term Virus was coined by
Louis Pasteur (1884).
• The word virus is derived from
the Latin word ‘vira’ meaning
poisonous fluid. (L. virus =
poison)
• Discovered the first virus –
Tobacco Mosaic Virus (TMV)
from Tobacco leaf by a Russian
scientist Iwanowski(1892)-
described as ‘filterable viruses’
• Study of viruses - Virology
• Obligate intracellular parasites –
require living cells of the host.
Outside the living cells of host,
viruses can be crystallized and
stored like a chemical substance.
Iwanowski(1892
• Viruses are called acellular microbes as they
lack the typical cellular organization -They
have no cell membrane, cytoplasm,
organelles etc.
• They possess their own genetic material
containing genetic codes for the synthesis of
nucleic acids and proteins needed for their
own replication.
• They utilize the ribosomes of the host cell for
protein synthesis during replication – hence
can not replicate outside the host cell.
• A fully formed virus particle after release
from the host cell does not increase in size or
number , but retain its infectious nature for
very long periods ranging from a few months
to several years.
• Viruses are considered as intermediate between
living organisms and non- living things.
Viruses have the properties of living organisms –
i. They have their own genetic material either
DNA or RNA
ii. They are capable of undergoing replication
iii. They have the ability to undergo mutation.
Viruses have the properties of non - living things –
i ) They are acellular microbes – they have no typical
cellular organization.
ii) They have no protein synthesizing machineries,
Ribosomes-They depend host ribosomes for
replication
iii) Outside the living cells of the host, viruses are
inactive and lifeless and can be crystallized as a
chemical substance.
Wendell Meredith Stanley
• W.M Stanley (1935)
crystallized virus –
Tobacco Mosaic Virus
(TMV) for the first
time.
• W. M Stanley is known
as the ‘Father of
Virology’
Image : https://www.nobelprize.org/

More Related Content

What's hot (20)

Nomenclature and classification of viruses
Nomenclature and classification of virusesNomenclature and classification of viruses
Nomenclature and classification of viruses
 
Virus
VirusVirus
Virus
 
Viriods and prions
Viriods and prionsViriods and prions
Viriods and prions
 
Viroids
Viroids Viroids
Viroids
 
Structure of viruses
Structure of virusesStructure of viruses
Structure of viruses
 
General Characteristics of Viruses
General Characteristics of VirusesGeneral Characteristics of Viruses
General Characteristics of Viruses
 
Virus detection identification
Virus detection identificationVirus detection identification
Virus detection identification
 
Differences between viroid and virion
Differences between viroid and virionDifferences between viroid and virion
Differences between viroid and virion
 
Cauliflower mosaic virus ppt
Cauliflower mosaic virus pptCauliflower mosaic virus ppt
Cauliflower mosaic virus ppt
 
33. an introduction to the viruses
33. an introduction to the viruses33. an introduction to the viruses
33. an introduction to the viruses
 
Viruses
VirusesViruses
Viruses
 
Classification and nomenclature of different groups of viruses
Classification and nomenclature of different groups of viruses Classification and nomenclature of different groups of viruses
Classification and nomenclature of different groups of viruses
 
Plant virus
Plant virusPlant virus
Plant virus
 
Viruses structure and classification
Viruses structure and classificationViruses structure and classification
Viruses structure and classification
 
Animal viruses
Animal virusesAnimal viruses
Animal viruses
 
Bacteriophages
Bacteriophages Bacteriophages
Bacteriophages
 
pox virus
pox viruspox virus
pox virus
 
VIRUSES CLASSIFICATION , LIFE CYCLE OF VIRUSES. CHARACTERISTICS OF VIRUSES
VIRUSES CLASSIFICATION , LIFE CYCLE OF VIRUSES. CHARACTERISTICS OF VIRUSES VIRUSES CLASSIFICATION , LIFE CYCLE OF VIRUSES. CHARACTERISTICS OF VIRUSES
VIRUSES CLASSIFICATION , LIFE CYCLE OF VIRUSES. CHARACTERISTICS OF VIRUSES
 
Retrovirus
RetrovirusRetrovirus
Retrovirus
 
Viroids
ViroidsViroids
Viroids
 

Similar to Viruses SMG

Similar to Viruses SMG (20)

Introduction to Virology
Introduction to Virology Introduction to Virology
Introduction to Virology
 
General Virology part 1.pdf
General Virology part 1.pdfGeneral Virology part 1.pdf
General Virology part 1.pdf
 
Viruses, structure, classification and characteristics
Viruses, structure, classification and characteristicsViruses, structure, classification and characteristics
Viruses, structure, classification and characteristics
 
General virology,Introduction, structure,classification - Copy.pptx
General virology,Introduction, structure,classification - Copy.pptxGeneral virology,Introduction, structure,classification - Copy.pptx
General virology,Introduction, structure,classification - Copy.pptx
 
Viruses
VirusesViruses
Viruses
 
Introduction to virus
Introduction to virusIntroduction to virus
Introduction to virus
 
Chapter 13 viruse
Chapter 13 viruseChapter 13 viruse
Chapter 13 viruse
 
Virus.ppt
Virus.pptVirus.ppt
Virus.ppt
 
Lect 1 introduction to medical virology
Lect 1 introduction to medical virologyLect 1 introduction to medical virology
Lect 1 introduction to medical virology
 
Morphology, Classification, Cultivation and Replication of Virus
Morphology, Classification, Cultivation and Replication of VirusMorphology, Classification, Cultivation and Replication of Virus
Morphology, Classification, Cultivation and Replication of Virus
 
Virology
VirologyVirology
Virology
 
Viruses
VirusesViruses
Viruses
 
3. structure of viruses
3. structure  of viruses3. structure  of viruses
3. structure of viruses
 
Viral genomes.pptx
Viral genomes.pptxViral genomes.pptx
Viral genomes.pptx
 
Viruses lecture 1
Viruses lecture 1Viruses lecture 1
Viruses lecture 1
 
Viruses – Morphology & Classification.pptx
Viruses – Morphology & Classification.pptxViruses – Morphology & Classification.pptx
Viruses – Morphology & Classification.pptx
 
Virus structure and classification
Virus structure and classificationVirus structure and classification
Virus structure and classification
 
Viruses ...in detail
Viruses ...in detailViruses ...in detail
Viruses ...in detail
 
Structure and diversity of virus
Structure and diversity of virusStructure and diversity of virus
Structure and diversity of virus
 
Viruses ppt
Viruses pptViruses ppt
Viruses ppt
 

More from sajigeorge64

Biostatistics Collection of Data and Sampling Techniques SMG.pptx
Biostatistics Collection of Data and Sampling Techniques SMG.pptxBiostatistics Collection of Data and Sampling Techniques SMG.pptx
Biostatistics Collection of Data and Sampling Techniques SMG.pptxsajigeorge64
 
Introduction to Biostatistics SMG .pptx
Introduction to Biostatistics  SMG .pptxIntroduction to Biostatistics  SMG .pptx
Introduction to Biostatistics SMG .pptxsajigeorge64
 
Linkage and Crossing-over.pptx
Linkage and Crossing-over.pptxLinkage and Crossing-over.pptx
Linkage and Crossing-over.pptxsajigeorge64
 
QUANTITATIVE INHERITANCE SMG
QUANTITATIVE INHERITANCE    SMGQUANTITATIVE INHERITANCE    SMG
QUANTITATIVE INHERITANCE SMGsajigeorge64
 
MULTIPLE ALLELES SMG
MULTIPLE ALLELES    SMGMULTIPLE ALLELES    SMG
MULTIPLE ALLELES SMGsajigeorge64
 
GENE INTERACTIONS SMG
GENE INTERACTIONS    SMGGENE INTERACTIONS    SMG
GENE INTERACTIONS SMGsajigeorge64
 
Introduction to Genetics - Mendelism SMG
Introduction to Genetics -  Mendelism    SMGIntroduction to Genetics -  Mendelism    SMG
Introduction to Genetics - Mendelism SMGsajigeorge64
 
AGENCIES OF POLLINATION SMG
AGENCIES OF POLLINATION    SMG  AGENCIES OF POLLINATION    SMG
AGENCIES OF POLLINATION SMG sajigeorge64
 
PLANT PEROXISOMES SMG
PLANT PEROXISOMES    SMGPLANT PEROXISOMES    SMG
PLANT PEROXISOMES SMGsajigeorge64
 
GOLGI APPARATUS, LYSOSOMES AND VACUOLES SMG
GOLGI APPARATUS, LYSOSOMES AND VACUOLES    SMGGOLGI APPARATUS, LYSOSOMES AND VACUOLES    SMG
GOLGI APPARATUS, LYSOSOMES AND VACUOLES SMGsajigeorge64
 
Changes In Number And Structure Of Chromosomes SMG
Changes In Number And Structure Of  Chromosomes    SMGChanges In Number And Structure Of  Chromosomes    SMG
Changes In Number And Structure Of Chromosomes SMGsajigeorge64
 
CELL CYCLE, MITOSIS & MEIOSIS SMG
CELL CYCLE, MITOSIS & MEIOSIS   SMGCELL CYCLE, MITOSIS & MEIOSIS   SMG
CELL CYCLE, MITOSIS & MEIOSIS SMGsajigeorge64
 
SPECIAL TYPES OF CHROMOSOMES SMG
SPECIAL TYPES OF CHROMOSOMES   SMGSPECIAL TYPES OF CHROMOSOMES   SMG
SPECIAL TYPES OF CHROMOSOMES SMGsajigeorge64
 
CHROMOSOME MODELS SMG
CHROMOSOME MODELS   SMGCHROMOSOME MODELS   SMG
CHROMOSOME MODELS SMGsajigeorge64
 

More from sajigeorge64 (20)

Biostatistics Collection of Data and Sampling Techniques SMG.pptx
Biostatistics Collection of Data and Sampling Techniques SMG.pptxBiostatistics Collection of Data and Sampling Techniques SMG.pptx
Biostatistics Collection of Data and Sampling Techniques SMG.pptx
 
Introduction to Biostatistics SMG .pptx
Introduction to Biostatistics  SMG .pptxIntroduction to Biostatistics  SMG .pptx
Introduction to Biostatistics SMG .pptx
 
Linkage and Crossing-over.pptx
Linkage and Crossing-over.pptxLinkage and Crossing-over.pptx
Linkage and Crossing-over.pptx
 
QUANTITATIVE INHERITANCE SMG
QUANTITATIVE INHERITANCE    SMGQUANTITATIVE INHERITANCE    SMG
QUANTITATIVE INHERITANCE SMG
 
MULTIPLE ALLELES SMG
MULTIPLE ALLELES    SMGMULTIPLE ALLELES    SMG
MULTIPLE ALLELES SMG
 
GENE INTERACTIONS SMG
GENE INTERACTIONS    SMGGENE INTERACTIONS    SMG
GENE INTERACTIONS SMG
 
Introduction to Genetics - Mendelism SMG
Introduction to Genetics -  Mendelism    SMGIntroduction to Genetics -  Mendelism    SMG
Introduction to Genetics - Mendelism SMG
 
AGENCIES OF POLLINATION SMG
AGENCIES OF POLLINATION    SMG  AGENCIES OF POLLINATION    SMG
AGENCIES OF POLLINATION SMG
 
PLANT PEROXISOMES SMG
PLANT PEROXISOMES    SMGPLANT PEROXISOMES    SMG
PLANT PEROXISOMES SMG
 
GOLGI APPARATUS, LYSOSOMES AND VACUOLES SMG
GOLGI APPARATUS, LYSOSOMES AND VACUOLES    SMGGOLGI APPARATUS, LYSOSOMES AND VACUOLES    SMG
GOLGI APPARATUS, LYSOSOMES AND VACUOLES SMG
 
STEM CELLS SMG
STEM CELLS    SMGSTEM CELLS    SMG
STEM CELLS SMG
 
MUTATIONS SMG
MUTATIONS   SMGMUTATIONS   SMG
MUTATIONS SMG
 
Changes In Number And Structure Of Chromosomes SMG
Changes In Number And Structure Of  Chromosomes    SMGChanges In Number And Structure Of  Chromosomes    SMG
Changes In Number And Structure Of Chromosomes SMG
 
CELL CYCLE, MITOSIS & MEIOSIS SMG
CELL CYCLE, MITOSIS & MEIOSIS   SMGCELL CYCLE, MITOSIS & MEIOSIS   SMG
CELL CYCLE, MITOSIS & MEIOSIS SMG
 
SPECIAL TYPES OF CHROMOSOMES SMG
SPECIAL TYPES OF CHROMOSOMES   SMGSPECIAL TYPES OF CHROMOSOMES   SMG
SPECIAL TYPES OF CHROMOSOMES SMG
 
CHROMOSOME MODELS SMG
CHROMOSOME MODELS   SMGCHROMOSOME MODELS   SMG
CHROMOSOME MODELS SMG
 
CHROMOSOMES SMG
CHROMOSOMES   SMGCHROMOSOMES   SMG
CHROMOSOMES SMG
 
RIBOSOMES SMG
RIBOSOMES   SMGRIBOSOMES   SMG
RIBOSOMES SMG
 
PLASTIDS SMG
PLASTIDS   SMGPLASTIDS   SMG
PLASTIDS SMG
 
MITOCHONDRIA SMG
MITOCHONDRIA   SMGMITOCHONDRIA   SMG
MITOCHONDRIA SMG
 

Recently uploaded

2.22.24 Black Nationalism and the Nation of Islam.pptx
2.22.24 Black Nationalism and the Nation of Islam.pptx2.22.24 Black Nationalism and the Nation of Islam.pptx
2.22.24 Black Nationalism and the Nation of Islam.pptxMaryPotorti1
 
11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdfAynouraHamidova
 
ICSE English Literature Class X Handwritten Notes
ICSE English Literature Class X Handwritten NotesICSE English Literature Class X Handwritten Notes
ICSE English Literature Class X Handwritten NotesGauri S
 
Creative, Technical, and Academic Writing
Creative, Technical, and Academic WritingCreative, Technical, and Academic Writing
Creative, Technical, and Academic WritingMYDA ANGELICA SUAN
 
Overview of Databases and Data Modelling-2.pdf
Overview of Databases and Data Modelling-2.pdfOverview of Databases and Data Modelling-2.pdf
Overview of Databases and Data Modelling-2.pdfChristalin Nelson
 
Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...
Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...
Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...Katherine Villaluna
 
Decision on Curriculum Change Path: Towards Standards-Based Curriculum in Ghana
Decision on Curriculum Change Path: Towards Standards-Based Curriculum in GhanaDecision on Curriculum Change Path: Towards Standards-Based Curriculum in Ghana
Decision on Curriculum Change Path: Towards Standards-Based Curriculum in GhanaPrince Armah, PhD
 
Nzinga Kika - The story of the queen
Nzinga Kika    -  The story of the queenNzinga Kika    -  The story of the queen
Nzinga Kika - The story of the queenDeanAmory1
 
A LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdf
A LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdfA LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdf
A LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdfDr.M.Geethavani
 
Digital Footprints to Career Pathways - Building a Strong Professional Online...
Digital Footprints to Career Pathways - Building a Strong Professional Online...Digital Footprints to Career Pathways - Building a Strong Professional Online...
Digital Footprints to Career Pathways - Building a Strong Professional Online...Sue Beckingham
 
11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdfAynouraHamidova
 
Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...
Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...
Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...AKSHAYMAGAR17
 
GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...
GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...
GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...Nguyen Thanh Tu Collection
 
BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...
BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...
BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...MohonDas
 
Genetic deterioration Seed ageing of improved variety seed, Maintenance of G...
Genetic deterioration  Seed ageing of improved variety seed, Maintenance of G...Genetic deterioration  Seed ageing of improved variety seed, Maintenance of G...
Genetic deterioration Seed ageing of improved variety seed, Maintenance of G...AKSHAYMAGAR17
 
skeletal system complete details with joints and its types
skeletal system complete details with joints and its typesskeletal system complete details with joints and its types
skeletal system complete details with joints and its typesMinaxi patil. CATALLYST
 
Data Modeling - Entity Relationship Diagrams-1.pdf
Data Modeling - Entity Relationship Diagrams-1.pdfData Modeling - Entity Relationship Diagrams-1.pdf
Data Modeling - Entity Relationship Diagrams-1.pdfChristalin Nelson
 
DISCOURSE: TEXT AS CONNECTED DISCOURSE
DISCOURSE:   TEXT AS CONNECTED DISCOURSEDISCOURSE:   TEXT AS CONNECTED DISCOURSE
DISCOURSE: TEXT AS CONNECTED DISCOURSEMYDA ANGELICA SUAN
 

Recently uploaded (20)

2.22.24 Black Nationalism and the Nation of Islam.pptx
2.22.24 Black Nationalism and the Nation of Islam.pptx2.22.24 Black Nationalism and the Nation of Islam.pptx
2.22.24 Black Nationalism and the Nation of Islam.pptx
 
11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 5-2023-Aynura-Hamidova.pdf
 
ICSE English Literature Class X Handwritten Notes
ICSE English Literature Class X Handwritten NotesICSE English Literature Class X Handwritten Notes
ICSE English Literature Class X Handwritten Notes
 
Creative, Technical, and Academic Writing
Creative, Technical, and Academic WritingCreative, Technical, and Academic Writing
Creative, Technical, and Academic Writing
 
first section physiology laboratory.pptx
first section physiology laboratory.pptxfirst section physiology laboratory.pptx
first section physiology laboratory.pptx
 
Overview of Databases and Data Modelling-2.pdf
Overview of Databases and Data Modelling-2.pdfOverview of Databases and Data Modelling-2.pdf
Overview of Databases and Data Modelling-2.pdf
 
Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...
Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...
Practical Research 1, Lesson 5: DESIGNING A RESEARCH PROJECT RELATED TO DAILY...
 
Capter 5 Climate of Ethiopia and the Horn GeES 1011.pdf
Capter 5 Climate of Ethiopia and the Horn GeES 1011.pdfCapter 5 Climate of Ethiopia and the Horn GeES 1011.pdf
Capter 5 Climate of Ethiopia and the Horn GeES 1011.pdf
 
Decision on Curriculum Change Path: Towards Standards-Based Curriculum in Ghana
Decision on Curriculum Change Path: Towards Standards-Based Curriculum in GhanaDecision on Curriculum Change Path: Towards Standards-Based Curriculum in Ghana
Decision on Curriculum Change Path: Towards Standards-Based Curriculum in Ghana
 
Nzinga Kika - The story of the queen
Nzinga Kika    -  The story of the queenNzinga Kika    -  The story of the queen
Nzinga Kika - The story of the queen
 
A LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdf
A LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdfA LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdf
A LABORATORY MANUAL FOR ORGANIC CHEMISTRY.pdf
 
Digital Footprints to Career Pathways - Building a Strong Professional Online...
Digital Footprints to Career Pathways - Building a Strong Professional Online...Digital Footprints to Career Pathways - Building a Strong Professional Online...
Digital Footprints to Career Pathways - Building a Strong Professional Online...
 
11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf
11 CI SINIF SINAQLARI - 2-2023-Aynura-Hamidova.pdf
 
Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...
Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...
Ideotype concept and climate resilient crop varieties for future- Wheat, Rice...
 
GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...
GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...
GIÁO ÁN TIẾNG ANH GLOBAL SUCCESS LỚP 11 (CẢ NĂM) THEO CÔNG VĂN 5512 (2 CỘT) N...
 
BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...
BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...
BEZA or Bangladesh Economic Zone Authority recruitment exam question solution...
 
Genetic deterioration Seed ageing of improved variety seed, Maintenance of G...
Genetic deterioration  Seed ageing of improved variety seed, Maintenance of G...Genetic deterioration  Seed ageing of improved variety seed, Maintenance of G...
Genetic deterioration Seed ageing of improved variety seed, Maintenance of G...
 
skeletal system complete details with joints and its types
skeletal system complete details with joints and its typesskeletal system complete details with joints and its types
skeletal system complete details with joints and its types
 
Data Modeling - Entity Relationship Diagrams-1.pdf
Data Modeling - Entity Relationship Diagrams-1.pdfData Modeling - Entity Relationship Diagrams-1.pdf
Data Modeling - Entity Relationship Diagrams-1.pdf
 
DISCOURSE: TEXT AS CONNECTED DISCOURSE
DISCOURSE:   TEXT AS CONNECTED DISCOURSEDISCOURSE:   TEXT AS CONNECTED DISCOURSE
DISCOURSE: TEXT AS CONNECTED DISCOURSE
 

Viruses SMG

  • 1. VIRUSES Dr Saji Mariam George Associate Professor Assumption College Autonomous Changanacherry.
  • 2. VIRUSES • The term Virus was coined by Louis Pasteur (1884). • The word virus is derived from the Latin word ‘vira’ meaning poisonous fluid. (L. virus = poison) • Discovered the first virus – Tobacco Mosaic Virus (TMV) from Tobacco leaf by a Russian scientist Iwanowski(1892)- described as ‘filterable viruses’ • Study of viruses - Virology • Obligate intracellular parasites – require living cells of the host. Outside the living cells of host, viruses can be crystallized and stored like a chemical substance. Iwanowski(1892
  • 3. • Viruses are called acellular microbes as they lack the typical cellular organization -They have no cell membrane, cytoplasm, organelles etc. • They possess their own genetic material containing genetic codes for the synthesis of nucleic acids and proteins needed for their own replication.
  • 4. • They utilize the ribosomes of the host cell for protein synthesis during replication – hence can not replicate outside the host cell. • A fully formed virus particle after release from the host cell does not increase in size or number , but retain its infectious nature for very long periods ranging from a few months to several years.
  • 5. • Viruses are considered as intermediate between living organisms and non- living things. Viruses have the properties of living organisms – i. They have their own genetic material either DNA or RNA ii. They are capable of undergoing replication iii. They have the ability to undergo mutation. Viruses have the properties of non - living things – i ) They are acellular microbes – they have no typical cellular organization. ii) They have no protein synthesizing machineries, Ribosomes-They depend host ribosomes for replication iii) Outside the living cells of the host, viruses are inactive and lifeless and can be crystallized as a chemical substance.
  • 6. Wendell Meredith Stanley • W.M Stanley (1935) crystallized virus – Tobacco Mosaic Virus (TMV) for the first time. • W. M Stanley is known as the ‘Father of Virology’ Image : https://www.nobelprize.org/
  • 7. SIZE OF VIRUSES • Vary widely in size – 10 to 20 nm (e.g. Parvo viruses( Latin parvus = small) -single-stranded DNA viruses) to 250 – 400 nm (Pox viruses ) • Smaller than bacteria • Visible only through an Electron Microscope Pox viruses(DsDNA viruses)
  • 8. SHAPE OF VIRUSES • Vary widely in shape Spherical Examples : Arboviruses Polio virus Japanese encephalitis Measles Influenza virus Mice leukaemia Cuboid Adenovirus Enteroviruses Retroviruses Arboviruses
  • 9. Spherical -Polio virus Image: http://theconversation.com/i
  • 10. Spherical -Japanese encephalitis virus Image :https://thenativeantigencompany.com/product/japanese-encephalitis-virus-ns1-protein/
  • 12. Spherical - Influenza virus IMAGE CREDIT: STEPHEN HARRISON
  • 16. Flexuous or coiled- Beet yellow virus (BYV)
  • 17. Rod shaped -Tobacco Mosaic Virus (TMV) Image : Plant Pathology Department of the Rothamsted Experimental Station collection of plant virus pictures
  • 18. Bullet shaped – Rabies virus Image: http://www.bioquicknews.com/node/1796
  • 19. Filamentous – Bacteriophage M13 Brick shaped – Pox virus
  • 20. Pleomorphic – Alfalfa Mosaic Virus (AMV) Image: Courtesy Dr M. Verhoyen & Mr S. Henstra.) Image:https://www.plantmanagementnetwork.org/pub/ php/brief/2012/honeysuckle/
  • 21. Complex morphology – having a head & tail Bacteriophage T 4 Image: uploaded by Ambekar Abdul Wahid
  • 22. Bacteriophage T 4 Image : http://textbookofbacteriology.net/phage.html
  • 23. Bacteriophage Lambda Image : https://www.deviantart.com/virionforlife/art/Bacteriophage-Lambda-515561927
  • 24. NATURE OF VIRUSES A virus can exist in two states – • An extracellular phase as an infectious virus particle or virion • An intracellular phase as the genetic material • Viruses are metabolically inert outside the living cells.
  • 25. STRUCTURE OF VIRUSES • Structure of a virus is simple • It consists of a central core of nucleic acid - the genome - either DNA or RNA surrounded by a protein coat , capsid and with or without an envelope. • The capsid with the enclosed nucleic acid is known as the nucleocapsid. • A virus contains only one type of nucleic acid , either DNA or RNA , but never both in the same virion and all the members of the same virus family have the same type of nucleic acid.
  • 26. Types of viruses based on nucleic acid : 1. RNA viruses (Riboviruses) The virus containing RNA as the genetic material. Most of the plant viruses are RNA viruses. Examples : Tobacco Mosaic virus (TMV ) Influenza virus Measles virus Polio virus
  • 27. Types of RNA viruses i) Single stranded RNA viruses (SsRNA viruses) • RNA is usually single stranded Examples : Tobacco Mosaic virus (TMV) Influenza virus Measles virus Mumps virus Brome Mosaic virus virus Papaya Mosaic virus Polio virus Picorna virus Toga virus Orthomyxovirus Rhabdovirus Foot & mouth disease virus Yellow fever virus. Ebola virus Rabies virus HIV virus
  • 28. ii)Double stranded RNA viruses (DsRNA viruses) • Viruses with double stranded RNA as the genetic material Examples Reo virus Wound tumour virus Rota virus Rice dwarf virus Blue tongue virus
  • 29. Distinct groups of RNA viruses : i) Viruses with Anti- sense RNA (asRNA) or negative – sense RNA • Viruses with single stranded RNA with a base sequence complementary to that of messenger RNA (mRNA) • During replication, it serves as a template for the transcription of viral complementary RNA. Examples: Measles virus, Ebola virus, Mumps virus, Rabies virus , Influenza virus
  • 30. ii ) Viruses with sense RNA or positive sense RNA • Viruses with single stranded RNA with the same base sequence as mRNA. • During replication, it functions as mRNA serving as a template for protein synthesis. Examples: Polio virus, Rubella virus, Yellow fever virus, Zika virus, Dengue fever virus, Tobacco Mosaic Virus.
  • 31. iii ) Viruses with a genome made up of several pieces of double stranded RNA Example : Reo virus iv ) Retro viruses Viruses with a single stranded RNA that is copied by reverse transcriptase into a DNA genome within the host cell. Examples: HIV -1 & HIV-2 that cause AIDS
  • 32. 2. DNA virus (Deoxy – virus) • Virus containing DNA as the genetic material. • Majority of animal and bacterial viruses are DNA viruses. Types of DNA viruses 1. Double stranded DNA virus (DsDNA Viruses) Examples Pox viruses – Small pox virus (Variola major & V. minor) ; Chicken pox virus ( Varicella zoster virus) ; Cow pox virus (CPXV) Caulimovirus e.g Cauliflower Mosaic Virus (CaMV) Adenovirus Hepatitis virus Papilloma virus Herpes simplex virus Bacteriophages of T – Series: T even bacteriophages – T2, T4, T6 & T- odd phages T1, T3, T5 , T 7.
  • 33. 2. Single stranded DNA viruses Examples : Phi – Chi 174 (ΦX174) Adeno - associated virus - 2 Parvovirus
  • 34. RNA – DNA VIRUSES • Rarely, a virus contains both RNA and DNA • Such viruses are called RNA – DNA viruses or ‘RNA-DNA hybrid virus’ or RDHV. • A DNA virus with the capsid of an RNA virus (inhabit Boiling Spring Lake, a city in North Carolina, United States, Goeff Diemer and Kenneth Stedman 2012).
  • 35. • In most viruses , the nucleic acid is a single molecule that may be linear or circular in nature. • However, some viruses have genomes that occur in several segments as in Orthomyxoviruses (e.g. Influenza virus ) , which have 7 or 8 SsRNA segments. • The protein coat is known as capsid – composed of many smaller units called capsomeres (Protomers).
  • 36. • The capsomers are made up of polypeptide chains. • The composition, number and forms of capsomers vary with the kinds of viruses. • The capsid gives shape to the virus. • It also protects the nucleic acid from inactivation by nucleases and other deleterious agents in environment • Another function of capsid is to introduce the viral genome into the host cells by adsorbing readily to cell surfaces.
  • 37. • Viruses may be non - enveloped (naked) or enveloped. • Majority of viruses are non-enveloped – They consist only one nucleic acid and protein coat. • In enveloped viruses (e.g. Influenza virus), there is an outer envelope or limiting membrane outside the capsid , which usually contain lipids and carbohydrates, which are generally derived from the host cell during virus replication.
  • 38. Structure of Tobacco Mosaic Virus (TMV) • The structure of a virus first elucidated was that of TMV (Franklin et.al., 1957). • It is a rigid , rod - shaped, helical virus. • Each virus particle is 300 nm long and 15 – 18 nm in diameter • TMV has a central core of single stranded RNA surrounded by a protein coat. • The protein coat consists of 2130 identical protein subunits called capsomeres (Protomers).
  • 39. • The capsomeres are arranged in a helical manner around the RNA. • The protein subunits are arranged around a central hole of 4nm. • There are 130 turns to the helix and 49 subunits for every 3 turns. • Each protein sub unit is made up of a single polypeptide chain , made up of 158 amino acids. • Inside the protein capsid there is a single stranded RNA molecule which is also spirally coiled to form helix.
  • 40. • Virus RNA consists of 6500 nucleotides. • Each turn of RNA helix contains 49 nucleotides • Thus each protein sub unit is associated with three nucleotide residues of RNA. • The protein coat serves as a protective tube . • The RNA is infective itself , although much less than the intact virus because the unprotected RNA is subjected to the action of nucleases and thus destroyed.
  • 41. HUMAN IMMUNODEFICIENCY VIRUS (HIV) • First isolated by Robert Galls (1993 , USA) and French Scientist Luc Montagnier . • HIV is a RNA retro virus (Oncogenic RNA viruses). • It causes Acquired Immuno Deficiency Syndrome (AIDS ) • AIDS is an immunoregulatory disorder that is often fatal because it predispose the person to severe opportunistic infections because of depletion of helper T cells, owing to infection by HIV. • HIV infects and destroys helper T cells leading to a number of immunological deficiencies. • HIV occurs in two main strains viz. HIV -1 and HIV -2.
  • 42. HIV • HIV is a spherical, enveloped virus, 90 – 120 nm in diameter.
  • 44. • HIV has an outer protein coat and an inner cone shaped core, enclosing the genome. • The genome is diploid , composed of two identical , single stranded, RNA copies which is unusual among viruses. • In association with the viral RNA is the reverse transcriptase enzyme (RNA dependent DNA polymerase) , which is a characteristic feature of retroviruses.
  • 45. • When HIV infects a host cell, the viral RNA is transcribed by the enzyme reverse transcriptase first into a single stranded DNA and then to a double stranded DNA (Provirus) which is integrated into the host cell chromosome by another enzyme integrase. • The virus can remain dormant for long periods. • Sometimes, in response to viral promoters, the provirus initiates viral replication by directing synthesis of viral RNA and other components.
  • 46. • The virus acquires a lipoprotein envelope from the host cell membrane while budding out of the cell. • The lipoprotein envelope consists of lipid derived from the host cell membrane and glycoproteins which are virus coded. • The major virus coded envelope proteins are the projecting knob like spikes (Peplomers) on the surface and the anchoring transmembrane pedicles.
  • 47. BACTERIOPHAGES (BACTERIAL VIRUSES) • Viruses that infect bacteria and destroy them – hence bacteriophages are also called as bacteria eaters. • First described by Twort (1915) and later by d’Herelle (1917). d’Herelle Image:https://microbiologysociety.org/publication/past-issues/world- war-i/article/frederick-william-twort-not-just-bacteriophage.html
  • 48. • Bacteriophages occur widely in nature in close association with bacteria. • Like all viruses, bacteriophages have a central core of nucleic acid , either DNA or RNA surrounded by a protein coat (capsid) made up of capsomeres (protomers).
  • 49. SHAPE OF BACTERIOPHAGES • Six morphological types (Bradley 1967) TYPE A : • Most complex type • Has a hexagonal head, rigid tail with a contractile sheath and tail fibres. Examples : T2, T4, T6 Bacteriophages (T – for Type)
  • 50. TYPE B : • Has a hexagonal head , a flexible tail with no contractile sheath and with or without tail fibres Examples : T1, T5 phages
  • 51. TYPE C : • Has a hexagonal head , a tail shorter than head with no contractile sheath and with or without tail fibres. Examples: T3, T 7 phages
  • 52. TYPE D : • Has a head made up of large capsomeres, but has no tail. Examples: Phi X 174 ( ΦX174 - Phi Chi 174 )
  • 53. TYPE E : • Has a head made up of small capsomeres, but has no tail. Examples: F2, MS2 phages
  • 54. TYPE F : • Filamentous phage Example : fd phage
  • 55. ‘GROUP G’ • Pleomorphic • Enveloped • No detectable capsid • Nucleic acid –DsDNA Example: MV – L 2
  • 56. NUCLEIC ACIDS • Phages have different nucleic acids • All tailed phages contain DsDNA • Phages with large capsomeres (Group D) and the filamentous phages (Group F) have SsDNA. • Group E phages have SsRNA • The DNAs of phages may be circular (e.g. ΦX174) . • In phage Lambda, the DNA is linear in the virion, but on entering the host cell, the cohesive ends join to form a circle.
  • 57. MORPHOLOGY AND STRUCTURE OF T4 BACTERIOPHAGE • The T – even phages (T2, T4, T6) have been studied in great detail and traditionally serve as the prototypes in describing the properties of bacteriophages. • Among the T – even phages , T4 bacteriophage is the most extensively studied coliphage. • It has a hexagonal head and a cylindrical tail • The virus is non – enveloped.
  • 58. MORPHOLOGY AND STRUCTURE OF T4 BACTERIOPHAGE
  • 59. • The elongated , hexagonal head contains a tightly packed core of circular, DsDNA, which is 1000 times longer than the phage itself, surrounded by a protein coat (capsid). • The DNA contains more than 75 genes. • The head is 100 nm long and 65 nm in diameter and consists of about 2000 identical protein subunits (Capsomeres). • The neck is very short and it contains a collar. • The neck connects the head with the tail.
  • 60. • The tail is long, helical (cylindrical) and is composed of a central hollow core or tube having a hole of 25 A°, through which the phage DNA passes into the host bacterial cell. • This is surrounded by a contractile sheath. • The contractile tube is spring like and it has 24 rings. Each ring is composed of 6 sub units. Thus the contractile tube is formed of 144 protein sub units.
  • 61. • The contractile sheath and the core of the tail remain attached to a hexagonal end plate (base plate) • The end plate contains six spikes or tail fibres. • Each of the tail fibres and tail spikes is a bundle of polypeptide chains. • The tail fibres help the phage to attach itself on to the bacterial cell wall.
  • 62. • The tail of T 4 phage is 100 nm in length and 25 nm in diameter. • The tail has the property of contraction which helps the phage in introducing its nucleic acid into the host bacterial cell .
  • 63. MULTIPLICATION OF VIRUSES • Viruses are obligate intracellular parasites which require the living cells of the host. • Outside the living cells of the host , viruses are inactive and lifeless and have no independent metabolic activity and are incapable of reproduction by processes characteristics of other microorganisms. • The multiplication of viruses take place by replication, in which the viral protein and nucleic acid components are synthesized within host cells.
  • 64. • The genetic information necessary for viral replication is contained in the viral nucleic acid. • However, virus has no protein synthesizing machinery (Ribosomes) and biosynthetic enzymes. • Hence virus utilize the biochemical machinery of the host cell to synthesize virus specific macromolecules required for the production of the virus progeny. • The general outline of the replication is similar in most viruses, but there are also differences among various groups.
  • 65. MULTIPLICATION OF BACTERIOPHAGES • Bacteriophages exhibit two types of life cycles i) Virulent or lytic life cycle (e.g. T4 Bacteriophage ) ii) Temperate or lysogenic life cycle (e.g. Lambda phage)
  • 66. i) Virulent or Lytic life cycle (e.g. T4 Bacteriophage ) • Exhibited by virulent phages. • Infect a bacterial cell and undergo multiplication which ends in the lysis of host bacterial cell releasing a large number of progeny phages. • A lytic life cycle has five sequential phases viz. adsorption, penetration, synthesis of phage components, assembly and maturation and release of progeny phages.
  • 67. i) Adsorption • A virulent bacteriophage comes into contact with a susceptible bacterium by random collision • Attaches to a specific receptor site on the bacterial surface with the help of the tail fibres.
  • 68. ii) Penetration • The phage drill a hole in the cell wall of the host bacterial cell by an enzyme lysozyme or activates the degradative enzymes of the host and injects its DNA into the bacterial cell. • After penetration, the empty head and tail of the phage remain outside the bacterium.
  • 69. iii) Synthesis of Phage components • After the entry into the host bacterial cell, the phage DNA directs the biosynthetic machinery of the host cell to shut down the normal cellular metabolism and to produce components of new virus particles. • The synthesis of bacterial mRNA and protein will be stopped within a few minutes and the bacterial DNA is quickly degraded into small fragments and the nucleoid region of the bacterium becomes dispersed. • The phage DNA, head protein and tail protein are synthesized separately in the bacterial cell.
  • 70. iv) Assembly and maturation • Assembly of phage DNA, head protein and tail protein . • Each component of phage nucleic acid acquires a protein coat and finally the tail structures are added forming a mature phage progeny.
  • 71. v) Release of phage progeny • Phage enzyme lysozyme causes the lysis of host bacterial cell wall resulting in the release of mature phage progeny • Usually , the lysis of E.coli takes place after about 22 minutes and approximately 300 T4 phage progeny are released.
  • 72. Lytic Life Cycle of a T4 Bacteriophage Image http://textbookofbacteriology.net/phage.html
  • 73. ii) Temperate or Lysogenic Life Cycle e.g. Lambda phage • A temperate phage does not cause the lysis of the host bacterial cell. • After entry into the host bacterial cell, the nucleic acid of the phage becomes integrated with the bacterial chromosome in a non-infectious stage known as prophage. • The prophage behaves like a segment of the host chromosome and replicates synchronously with it. • The bacterium that carries a prophage within its genome is called a lysogenic bacterium. • As the bacterium reproduces, the viral nucleic acid is transmitted to the daughter cells at each binary fission.
  • 74. Lysogenic Life Cycle (Lambda phage)
  • 75. • The prophage gives some new properties to the lysogenic bacterium – Lysogenic conversion. • This is due to the synthesis of new proteins that are coded by the prophage DNA. • Occasionally, during the multiplication of the lysogenic bacterium, the prophage may become ‘excised’ from certain cells. • This prophage may be converted into virulent phages spontaneously and initiates the lytic replication and phage progenies are released which can infect other bacterial cells and render them lysogenic. This is known as spontaneous induction of prophage – rare event. • A lysogenic bacterium is resistant to reinfection by the same or related phages – ‘superinfection immunity’.

Editor's Notes

  1. Cow pox virus
  2. Fig . Phi – Chi !74
  3. T 4 phages , T 2 phages
  4. T 1 phage , T 5 phage
  5. T 7 phage
  6. MS2 phage,
  7. Coloured TEM of fd phage