Viral Exit + DNA Viruses

Question 1

How is poliovirus assembled?

Answer 1

The virus attaches to pvr and uncoats at the cell membrane
Proteins are made as polyproteins, the initial cleavage is autocatalyzed but then proteases are released
The capsid proteins auto assemble in a concerted assembly with RNA

Question 2

What forces are favoured in the intact polyprotein?

Answer 2

Intramolecular interactions

Question 3

What does the cleavage of VP0 to VP2 and VP4 require?

Answer 3

RNA

Question 4

What happens if RNA is not present in the capsid?

Answer 4

The final cleavage cannot occur and the capsid falls apart

Question 5

What are packaged in the HIV virion?

Answer 5

Integrase and reverse transcriptase

Question 6

How does HIV replicate?

Answer 6

It inserts itself into the genome and uses the host transcriptional machinery to make more copies and can also allow alternate splicing of transcripts

Question 7

Why does HIV integrate into the genome?

Answer 7

Producing proteins would make it susceptible to a T-cel response, so it does this to hide

Question 8

How are viral proteins localized to the cellular membrane?

Answer 8

Secreted or TM proteins are made on the RER and secreted into the ER lumen or left in the ER membrane

RER buds off into the Golgi, and Golgi buds off into rough vesicles that fuse with the cell membrane = the assembly of enveloped versus frequently takes place at the plasma membrane

Question 9

What enzyme is required for the replication of polio and herpes?

Answer 9

DNA-dependent RNAP

Question 10

What are 3 common mechanisms in exponential viral DNA replication?

Answer 10

Template directed

Each strand is copied beginning at the origins

Uses a DNA-dependent DNAP

Question 11

Why does herpes trick the cell to go into S phase?

Answer 11

Generation of dNTP for DNA synthesis are only present in the S phase

Question 12

What do larger viruses encode?

Answer 12

Their own enzymes

Question 13

What are the properties of replicons in mammalian and viral DNA?

Answer 13

Bidirectional replication from an ori
Most common pattern of replication of DNA of host and viral genomes
AT rich

Question 14

What is semi-discontinuous DNA synthesis initiated by and how are the leading and lagging strands formed?

Answer 14

A primase
-synthesis of the leading strand starts from ori on the RNA primer
-lagging strand proceeds in short pieces called okazaki fragments

Question 15

What does discontinuous synthesis leave unfinished?

Answer 15

The lagging strand

Question 16

What does the removal of the primer from the 5’ end create?

Answer 16

A gap that cannot be filled

Question 17

What do successive rounds of DNA lead to unless there is special machinery in place?

Answer 17

Loss of genetic material

Question 18

How does herpesvirus solve the end problem?

Answer 18

With the rolling circle mechanism of DNA replication

Question 19

How does the rolling circle mechanism of DNA replication work?

Answer 19

1. nick one strand
2. replicate by continuous copying = continuous DNA synthesis from the 3’ OH end
3. displace strand
4. further continuous and discontinuous DNA synthesis
5. complete the lagging strand
6. dsDNA templates result
7. keep making more copies by continuing around again

Question 20

How doe direct repeats at the ends of herpes DNA package one genome?

Answer 20

Proteins bind to specific sequences at the ends and an empty capsid binds these proteins
DNA is stuffed in until proteins on the other ends are reached and the DNA is cleaved

Question 21

Where does viral DNA synthesis occur?

Answer 21

Specialized compartments
DNA templates and enzymes are sequestered into discrete sites in the nucleus

Question 22

What do the products of one replication cycle become?

Answer 22

Templates for the next

Question 23

What enzymes can proofread during DNA synthesis of herpesvirus?

Answer 23

Host DNAP can proofread, viral DNAP cannot

Question 24

What is acyclovir converted to in regard to DNAP?

Answer 24

Converted to a product that competitively inhibits HSV DNA polymerase

Question 25

What does the reproductive cycle of herpes involve?

Answer 25

The first proteins synthesized are transcriptional activator of genes that make proteins needed later in synthesis
Late proteins are required for capsid assembly and membrane proteins

Question 26

Where are latent infections localized?

Answer 26

In neurons

Question 27

How do infections maintain latency?

Answer 27

Transcripts are produced from parts of the genome to produce proteins required to maintain latency