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LECTURE 33: Viral Evolution

LECTURE 33: Viral Evolution. By Randall Fisher B.Sc. MBS 2355827@uwc.ac.za. Structure of this lecture:. Split into groups (ten groups of 12.794 students) Recap of last lecture 3 Theories of Viral Origin 3 minute and 47 second interval Baltimore scheme of Viral Classification Questions.

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LECTURE 33: Viral Evolution

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  1. LECTURE 33: Viral Evolution By Randall Fisher B.Sc. MBS 2355827@uwc.ac.za

  2. Structure of this lecture: • Split into groups (ten groups of 12.794 students) • Recap of last lecture • 3 Theories of Viral Origin • 3 minute and 47 second interval • Baltimore scheme of Viral Classification • Questions

  3. !!!RECAP!!!

  4. Question 1 • What is the approximate size of the largest RNA Viral genome? • And the largest DNA Viral genome?

  5. Question 2 • DNA or RNA?

  6. 3’ UAC 5’ Question 3 • A: Positive sense • B: Negative sense • C: Nonsense • D: 50 cents

  7. Question 4 • What attribute, exclusive to Viral RNA genomes, does this image demonstrate? DNA RNA

  8. 5’ 3’ Question 5 • What the hell is that? AAAAAAAAAAAAAAAAAAAA

  9. Question 6 • What is the name of the subfamily of Orthomyxoviruses that is clinically important to man (and woman… well… some of them).

  10. Question 7 • How are Paramyxoviruses transmitted?

  11. Question 8 • What is the shape of the Rhabdovirus virion? A B C D

  12. Question 9 • Which virus is Prof. Fieldings favorite virus?

  13. Question 10 • Which RNA virus synthesizes the enzyme Reverse Transcriptase?

  14. Theories of Viral Origin • Regressive theory • Degenerate forms of parasites • Mitochondria and chloroplasts? • Progressive theory • Normal cellular n.a. ability to replicate autonomously, • DNA viruses = plasmids or transposable elements. • Retroviruses = retrotransposons • RNA virus = mRNA. • Coevolution theory: • Viruses coevolved with life

  15. ITS HAMMER TIME

  16. LECTURE 34: The Baltimore Scheme of Viral Classification By: the same old guy With the same old B.Sc. 2355827@uwc.ac.za

  17. Baltimore Scheme of Viral Classification • Scheme that encompass all viruses, based on the: • nature of genomes (type of nucleic acids) • Modes of replication and gene expression • May not be phylogenetic, no common origin • Used by International Committee on Taxonomy of Viruses (ICTV) with other parameters • Revised Baltimore scheme based on fundamental importance of mRNA in the replication cycle of viruses • Viruses do not contain the molecules necessary to translate mRNA, rely on host cell machinery

  18. Baltimore Scheme of Viral Classification • They must make mRNA that can be recognized by host cell ribosomes • Either the genes are stored in the 5'→3' direction (positive or + polarity), analogous to the direction in which genes are represented in mRNA in cells,

  19. Baltimore Scheme of Viral Classification • or the genes are stored in the opposite, 3'→5' direction (negative or - polarity). • In other words: + or - polarity of RNA: • "+" is able to serve as mRNA. • "-" is the complement of “+”, must function as template to make a complementary strand of + RNA before any translation can occur.

  20. Lets get cracking! • DNA viruses • Group I - dsDNA viruses (double stranded DNA) • mRNA may come from either strand and transcription similar to host’s • Group II - ssDNA viruses (single stranded DNA) • DNA + or – depending on virus studied • DNA converted to ds before synthesis of mRNA

  21. RNA Viruses: Group III • RNA viruses • Group III - dsRNA viruses (double stranded RNA) • Most of these viruses have segmented genomes • mRNA from one template of each segment • Mechanism similar to transcription from dsDNA genome • Enzymes needed not in uninfected cells • Enzymes encoded by virus, packaged in virion, carried into cell

  22. Group IV • Group IV - (+)ssRNA viruses (positive single stranded RNA or mRNA like) • Same sense as mRNA (+), can be translated • Enzymes for RNA synthesis virus encoded, made after infection initiated

  23. Group V • Group V - (-)ssRNA viruses (negative single-stranded RNA) • Genomes complimentary to mRNA (- sense) • Synthesis of mRNA by transcription from genome strand • Requires novel virus encoded enzymes • Some Group V viruses are known as ‘ambisense’ viruses • These use newly made ‘antigenome’ RNA strand as template for mRNA production and Enzymes needed also virus encoded

  24. Reverse Transcribing Viruses: Groups VI and VII • DNA and RNA Reverse Transcribing viruses • Group VI - ssRNA-RT viruses (single stranded RNA) • Generate dsDNA intermediate before replication • Carried out by reverse transcriptase enzyme; carried in virion • Group VII - dsDNA-RT viruses (double stranded DNA) • Also known as “reversiviruses” • Replication strategy via positive-sense ssRNA intermediate and RT enzyme • Inverse, but similar to VI

  25. The END!!! • For now…

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