Viruses lecture 1
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The document provides an overview of virology, defining viruses as acellular organisms that replicate inside host cells and can cause diseases in humans, animals, and plants. It discusses the characteristics, types, structure, and replication mechanisms of viruses, as well as the differences between naked and enveloped viruses, viroids, and prions. Key historical figures and methods of analysis, such as electron microscopy and x-ray crystallography, are also mentioned.
Viruses lecture 1
- 1. Viruses
- 2. General Virology Concept of virology Viruses Types of viruses Viral characteristics Virion Size and Shape Structure Replication Viral Variation Classification
- 3. Concept of Virology • Virology is the bioscience for study of viral nature, and the relationship between virus and host. • Viruses often cause serious diseases, relate to some cancers and congenital deformities, also can be used as tool for genetic engineering.
- 4. Definition of Virus Viruses may be defined as acellular organisms whose genomes consist of nucleic acid protected by the protein coat, and which obligately replicate inside host cells and too small to be seen by electron microscopy.
- 5. History L. Pasteur in 1884 and A. Mayer in 1886 • Studied on mosaic disease of Tobacco plant/ transformation of disease D. Iwanowsky in 1892 • Studied on extract from tobacco plant suffering from mosaic disease. Filtration mechanism M. Beijernick in 1898 • Disease causing filterable viruses multiply in host F. Twort and F.d herelle • Some viruses infect bacteria called bacteriophage W. Stanley in 1935 • Demonstrate the structure of plant virus that was Tobacco Mosaic Virus (TMV)
- 6. Viral Properties/ Characteristics • Viruses are inert (nucleoprotein ) filterable agents • Viruses are obligate intracellular parasites • Viruses cannot make energy or proteins independent of a host cell • Viral genome are RNA or DNA but not both. • Viruses have a naked capsid or envelope with attached lipoproteins • Viruses do not have the genetic capability to multiply by division. • Viruses are non-living entities
- 7. Consequences of Viral Properties • Viruses are non living out side the cell • Viruses are disease causing agent • Viruses must be able to use host cell processes to produce their components (viral messenger RNA, protein, and identical copies of the genome) • Viral components must self-assemble • The fully assembled infective particle is called Virion.
- 8. Challenges the way we define life • viruses do not respire, • they do not move • they do not grow • they do most certainly reproduce, and may adapt to new hosts.
- 9. Types Of Viruses Animal viruses: • cause disease in man and animals. • Contain DNA core covered by capsid. Plant viruses: •cause disease in plants. •Contain RNA core covered by protective protein.
- 10. TypesOf Viruses Retroviruses: • cause disease in humans • containing RNA as genetic material. Gemini viruses: • cause disease in plants. • Contain ss-DNA as genetic material
- 11. Size and Shape • Methods • Size of Viruses • Shapes of Viruses
- 12. Methods of Analysis • Electron microscopy : The resolution is 5nm (1nm = 10-9 m) • X-ray crystallography
- 14. Size of Viruses/ Architechture A small virus has a diameter of about 20nm. Parvovirus A large virus have a diameter of up to 400nm. Poxviruses
- 17. Shape of Viruses/ Architecture • Rounded • Rod-shaped • Brick-shaped • Tadpole-shaped • Bullet-shaped • Filament
- 18. Shapes of Viruses: Rounded (Mumps virus, Influenza virus)
- 19. Shapes of Viruses :Rod-shaped (TMV)
- 20. Shapes of Viruses :Brick-shaped (Pox virus) .
- 22. Shapes of Viruses :Bullet-shaped (Rhabdo viruse)
- 23. Shapes of Viruses :Filament (paramyxoviruses)
- 24. QUIZ???? What is Virus???? What are the types of virus??? Write the name of two shape of viruses with example Don’t Cheat
- 26. Virus •Non-cellular •Disease causing agent •Nucleic acid •Capsid •Lipoprotien
- 28. Viral core • Viral core The viral nucleic acid genome, In the center of the virus. Control the viral heredity and variation, responsible for the infectivity.
- 29. Genome • The genome of a virus can be either DNA or RNA • DNA-double stranded (ds): linear or circular Single stranded (ss) : linear or circular • RNA- ss: segmented or non-segmented ds: linear (only reovirus family)-not circular
- 30. DNA RNA double- stranded single- stranded double- stranded single-stranded lin ear circular lin ear circular linear linear (circular)* sin gle multi ple (+)sense (-)sense Viral RNA Protein synthesis
- 32. Viral Capsid • The protein shell, or coat, that encloses the nucleic acid genome. • Functions: • a. Protect the viral nucleic acid. • b. Participate in the viral infection. • c. Share the antigenicity
- 33. Nucleocapsid •The core of a virus particle consisting of the genome plus a complex of proteins. • complex of proteins = Structural proteins +Non- Structural proteins (Enzymes & Nucleic acid binding proteins)
- 34. Capsomeres •The viral coat (capsid) are often built up of identical repeating units called capsomeres
- 35. Symmetry of Nucleocapsid • Helical • Cubic /Icosahedral • Complex
- 36. Helical • Helical symmetry • Containing RNA core • Capsid cover with capsomeres • Mostly Rod shaped • Including animal and plant virus
- 37. Example of Helical TMV Coronavirus Hantavirus Influenza Virus (Flu Virus) Measles Virus ( Rubeola) Mumps Virus Parainfluenza Virus Rabies Virus Respiratory Syncytial Virus(RSV)
- 38. Cubicor icosahedral symmetry • Cubic or icosahedral symmetry • Identical 20 triangularunits arranged in cluster of five or six, 12 corner and 30 edges • covered with capsomeres • Mostly spherical shaped • Including animal virus
- 42. Example of Icosahedral 1. Adenovirus 2. Hepatitis Virus Hepatitis A Virus (HAV) Hepatitis B Virus (HBV) Hepatitis C Virus (HCV) Hepatitis Delta Virus (HDV) Hepatitis E Virus (HEV) 3. Herpes Virus Herpes Simplex Virus 1 (HHV1) Herpes Simplex Virus 2 (HHV2) 4. Human Immunodeficiency Virus (HIV) 5. Human T-lymphotrophic Virus (HTLV) 6. Polio virus 7. Rhinovirus 8. Rubella Virus
- 43. Complex Virus Structures • Uncertain symmetry • Proteins and lipoproteins • A well known example is the tailed bacteriophages. • The head of these viruses is cubic with a triangulation number of 7. This is attached by a collar to a contractile tail with base plate and tail fibril
- 44. T4 Bacteriophage
- 45. QUIZ???? Write about the symmetry of nucleocapsid?? Don’t be cheater
- 48. Properties of naked viruses • Stable in hostile environment • Not damaged by drying, acid, detergent, and heat • Released by lysis of host cells • Can sustain in dry environment • Can infect the GI (gastrointestinal tract) and survive in the acid condition • Can spread easily via hands, dust, fomites, etc • Can stay dry and still retain infectivity • Neutralizing mucosal and systemic antibodies are needed to control the establishment of infection
- 49. Naked viruses( Non Enveloped ) Example Hepatitis A Virus (HAV) Hepatitis E Virus (HEV)
- 51. Envelope
- 52. Envelope •A lipid-containing membrane that surrounds some viral particles. • It is acquired during viral maturation by a budding process through a cellular membrane, Viruses-encoded glycoproteins are exposed on the surface of the envelope. • Not all viruses have the envelope, and viruses can be divided into 2 kinds: enveloped virus and naked virus.
- 53. Functions of envelope • Antigenicity some viruses possess neuraminidase (The enzyme helps viruses to be released from a host cell). • Infectivity • Resistance
- 55. Properties of enveloped viruses • Labile in dry , arid environment • Damaged by drying, acid, detergent, and heat • Pick up new cell membrane during multiplication • Insert new virus-specific proteins after assembly • Virus is released by budding
- 56. Consequences of Properties for enveloped viruses • Must stay moist • Must not infect the GI tract for survival • Must be transmitted by droplets, secretions, blood and body fluids • Must re-infect another host cell to sustain • Humoral and cell-mediated immunity are needed to control the infection
- 58. Enveloped • California Encephalitis Virus • Coronavirus • Hantavirus Hepatitis B Virus (HBV) Hepatitis C Virus (HCV) Hepatitis Delta Virus (HDV) Herpes Simplex Virus 1 (HHV1) • Rotavirus • Rubella Virus Smallpox Virus (Variola) Vaccinia Virus • Herpes Simplex Virus 2 (HHV2) Human Immunodeficiency Virus (HIV) Human T-lymphotrophic Virus (HTLV) Influenza Virus (Flu Virus) Polio virus Rhinovirus Yellow Fever Virus
- 59. Spike or Peplomer A peplomer is a glycoprotein spike on a viral capsid or viral envelope. These protrusions will only bind to certain receptors on the host cell, they are essential for viral infectivity.
- 61. QUIZ???? Write the difference between naked and enveloped virus?? Don’t be cheater
- 62. Viroids •Viroids are small (200-400nt), circular RNA molecules with a rod-like secondary structure which possess no capsid or envelope which are associated with certain plant diseases. Their replication strategy like that of viruses - they are obligate intracellular parasites.
- 63. Viroids • Viroids are small (200-400nt), circular RNA molecules with a rod-like secondary structure which possess no capsid or envelope which are associated with certain plant diseases. Their replication strategy like that of viruses - they are obligate intracellular parasites.
- 64. (Prions) • Prions are rather ill-defined infectious agents believed to consist of a single type of protein molecule with no nucleic acid component. Confusion arises from the fact that the prion protein & the gene which encodes it are also found in normal 'uninfected' cells. These agents are associated with diseases such as Creutzfeldt-Jakob disease in humans, scrapie in sheep & bovine spongiform encephalopathy (BSE) in cattle.
Editor's Notes
- #57: Humoral Immunity - this involves the use of antibodies produced by the b cells to attack any invading foreign bodies like bacteria, viruses etc. Production of memory cells also takes place for a faster response in case of a second infection. Cell mediated immunity- this involves the destruction of self cells damaged by mutations or infected by viruses. this form of immunity includes cells like cytotoxic t cells nk cells.