Lecture 18: Viruses Part 2 Flashcards
Genomes: RNA
•RNA genomes can be either +, -, or ds (double stranded)
(+) RNA
The genome is in mRNA form and can be made directly into protein once in enters cell
(-) RNA
The complimentary strand to an mRNA and therefore needs to be copied into mRNA before proteins can be produced. Needs these enzymes packaged into virion
dsRNA
Has both + and - strands and is usually copied into mRNA before proteins can be produced
What polymerase enzymes do humans have
DNA polymerase- DNA ->DNA
RNA polymerase- DNA -> RNA
Ribosome- RNA -> protein
Why do viruses mutate so frequently?
DNA dependent DNA polymerase
-Proofreading- DNA repair (mutations 1 in 100 million nt)
RNA dependent RNA polymerase
-No proofreading (mutations 1 in 100,000 nt)
•RNA genomes are more prone to mutation because viral RNA polymerase and reverse transcriptase don’t have elaborate proofreading abilities
Reverse transcriptase
RNA dependent DNA polymerase
What other factors contribute to mutations?
•Number of circulating strains
•Segmentation of the genome
•Type of genome
•Rate of replication
Mutation types
-Antigenic drift
-Antigenic shift
Antigenic drift
Due to point mutations in genome over time due to replication
Antigenic shift
Due to reassortment of two or more genomes to make new virus strain
Why do segmented genomes matter?
Reassortment (2^n)
-Influenza (8 strands)=256 new assortments
-Rotavirus (11 strands)=2048 new assortments
Assembly
•Assembly of a virion can occur in cytoplasm, nucleus, or golgi (coronavirus)
•Packaging is the loading of genetic material into capsid
Exit
-Budding of enveloped viruses (use small portion of membrane to form envelope while exiting cell)
-Bursting of non-enveloped viruses
Growing viruses
•Viruses must be grown in host cells
-Living animals
-Embryonated eggs
-Cell culture
