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Medical Virology Lecture 31 (finally!) The DNA Viruses

Medical Virology Lecture 31 (finally!) The DNA Viruses. Tasnim Suliman 2535939@uwc.ac.za Molecular Virology Lab MBS dept - UWC. Replication of nucleic acids. Series of highly ordered events that involve: Viral protein synthesis mRNA production Genome replication

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Medical Virology Lecture 31 (finally!) The DNA Viruses

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  1. Medical VirologyLecture 31 (finally!)The DNA Viruses Tasnim Suliman 2535939@uwc.ac.za Molecular Virology Lab MBS dept - UWC

  2. Replication of nucleic acids • Series of highly ordered events that involve: • Viral protein synthesis • mRNA production • Genome replication • DNA viruses except poxviruses: • replicate in the nucleus of the host cell • Use host cell RNA polymerase II to transcribe their genes to mRNA • RNA viruses except influenza and retroviruses: • Replicate in cytoplasm • Replication strategy depends on nature of virus

  3. Classification of viruses based on the following aspects: • Virus morphology - size, shape, type of symmetry, etc. • Virus genome properties - type of n.a., size of genome, etc. • Physiochemical properties - molecular mass, pH stability, etc. • Virus protein properties - number, size, modifications, etc. • Genome organization and replication - gene order, number and positions of ORF, cellular sites, etc. • Antigenic properties • Biological properties - natural host range, vector relationships, tissue tropisms

  4. How do viruses enter the body? • Via inhaled droplets (rhinovirus) • In food or water (hepatitis A) • By direct transfer from other infected hosts (HIV) • From bites of vector arthropods (yellow fever)

  5. Infection of a susceptible cell does not automatically insure that viral multiplication will ensue and that viral progeny will emerge • Infection of susceptible cells may be: • Productive: permissive cells and is characterized by production of infectious progeny. • Abortive: can occur for two reasons. • cell may be susceptible to infection, it may be non-permissive allowing a few, but not all, viral genes to be expressed • also result from infection defective viruses, which lack a full complement of viral genes. • Restrictive/restringent: cells transiently permissive. • virus persists in the cell until the cell becomes permissive • or only a few of the cells in a population produce viral progeny at any time

  6. DNA TUMOR VIRUSES • DNA tumor viruses have two life-styles: • In permissive cells, all parts of the viral genome are expressed. This leads to viral replication, cell lysis and cell death • In cells non-permissive for replication, viral DNA is integrated into the cell chromosomes (usually but not always) at random sites. Only part of the viral genome is expressed.

  7. Types of infection patterns • lytic infection • destroys host cells. • persistent infection • host cell continues to shed virus over long time. Cell gradually becomes recognizably poorer (recognized as cytopathic effect, or CPE) • Transformation • infection by certain viruses causes cells to change, become cancerous • Responsible genes are called oncogenes • latent infection • virus genes may not be expressed for long time (ex. many Herpes infections). • genes are not integrated into host chromosome.

  8. Replication of DNA Viruses (recap) NB. Papovaviridae is now divided into Polyomaviridae and Papillomaviridae

  9. DNA Viruses * * NB. Papovaviridae is now divided into Polyomaviridae and Papillomaviridae

  10. DNA - containing viruses • Parvoviruses • Diameter:18-26nm • Cubic symmetry • No envelope • ss DNA • Genome size: 5.6kbs • eg.Human parvovirus B 19

  11. Polyomaviruses • Diameter: 40nm • Cubic symmetry • no envelope • ds DNA • Genome size:5kbs • eg. SV40, may cause tumors

  12. Papillomavirus • Similar to polyomaviruses • Diameter: 55nm • Genome size: 6.8 - 8.4kbs (larger than polyomaviruses) • In humans: May cause warts and genital cancers. • Eg. Human Papaillomavirus (HPV)

  13. Adenovirus • 47 types infect humans • Diameter:70-90nm • Cubic symmetry • no envelope • ds DNA, • Genome size: 26 - 45kbs • Cause acute respiratory disease, conjunctivitis and gastroenteritis Adenovirus structure

  14. Hepadnaviruses • Diameter: 40-48nm • Icosahedral • enveloped • ds DNA • Genome size:3.2kbs • Causes acute chronic hepatitis ~ high risk of developing liver cancer

  15. Herpesviruses • Diameter:150-200nm • Cubic symmetry • enveloped • ds DNA • Genome size: 125 - 240kbs -eg. Varicella-zoster virus (chicken pox and measles), Epstein-Barr virus (EBV) and cytomegalovirus (CMV).

  16. Poxviruses • Brick-shaped or ovoid • Size: 220-450nm long x 140-260nm wide x 140-260nm thick • Enveloped • ds DNA • Genome size:130-375kbs (large!) • Produce skin lesions eg. Small pox and vaccina virus

  17. Poxviruses (continued) Figure 1. Structure of the variola virus

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