Lecture 5 - Viral Genetics and Replication

Question 1

What are the steps in Viral Replication?

Answer 1

1. Virions bind to receptors on host cell surface
2. Virion (or viral genome) enters the cell
3. Early viral genes are expressed
4. Early viral proteins direct replication of viral genomes
5. Late mRNAs are made from newly replicated genomes
6. Late viral proteins package viral genomes and assemble virions
7. Progeny virions are released from the host cell

Question 2

What are the viral genomes?

Answer 2

they are in the picture

Question 3

What is involved in the DNA Virus Replication Cycle?

Answer 3

• DNA viruses need to make mRNAs to be translated into proteins by host cell machinery

Viruses need to replicate its genome
Early gene expression
Enzymes, regulatory proteins
Late gene expression
Proteins needed for assembly

Question 4

What does it mean when a virus takes over the cell machinery?

Answer 4

• Some viruses rely on host cell machinery for DNA replication

Induce S phase
SV40 T antigen
Binds to origin region of genome
Binds/activates DNA polymerase a
Binds and inactiates tumor suppressor proteins (p53)

Question 5

What is special about ss/dsDNA viruses when they use an RNA intermediate?

Answer 5

• Parts of genome are dsDNA and others ssDNA (gaps)
• Virus carries it’s own reverse transcriptase
• dsDNA enters the nucleus, forms an circular episome
• Virus does not encode an integrase gene

Question 6

What is involved in Positive and negative sense ssRNA?

Answer 6

Viruses containing +ssRNA genomes can be directly translated using host cell machinery
Genome must encode a replicase that produces viral genomic RNA
Viruses containing –ssRNA genomes must be transcribed into mRNA before translation can occur
Viruses must possess an RNA-dependent RNA polymerase (RdRP) that will synthesize the viral +ssRNA, mRNAs, and ssRNA viral genomes
Transcriptase and replicase activity