Virology Final Part 5

Question 1

What is antigenic drift?

Answer 1

Minor changes in glycoproteins due to the accumulation of changes in the amino acid sequence and result in minor antigenic differences

Question 2

What is antigenic shift?

Answer 2

If two different influenza strains infect the same cell, the genes re-assort and can result in a strain that no one has immunity to

Question 3

How do NA inhibitors work and what are two examples of them?

Answer 3

-

- tamiful and relenza

Question 4

How do ion channel inhibitors work and what are two examples?

Answer 4

• block the release of influenza by blocking the M2 protein

- symmetrel and flumadine

Question 5

How does influenza develop drug resistance?

Answer 5

A mutation in the gene that codes for the ion channel M2– it could change such that the drug no longer interacts with the protein

Question 6

How are retroviruses characterized?

Answer 6

A long interval between the initial infection and the onset of serious clinical symptoms

Question 7

Where was the origin of the two types of HIV?

Answer 7

HIV-1: North America

HIV-2: isolated from AIDS patients in West Africa

Question 8

What are the four groups of HIV-1?

Answer 8

M,N,O and P

Question 9

What are CRFs?

Answer 9

Circulating recombinant forms

Question 10

What is the structure of HIV?

Answer 10

• Enveloped, spherical to pleomorphic, matrix layer, spike proteins gp120 and gp41
• inside: nucleocapsid + genome= 2 strands of ssRNA (+), RT, integrase, Vif, Vpr, Nef, p7, protease,

Question 11

Where does the tRNA associated with HIV come from?

Answer 11

The host cell from the previous infection

Question 12

Is the first step in HIV replication translation on a ribosome?

Answer 12

No— the virus is not completely uncoated, and the RT happens in the core fo the virus

Question 13

How does HIV cleave its polyprotein?

Answer 13

• it cleaves the polyprotein using a protease, but there is never gag-env-pol, it’s either gag or gag-pol

Question 14

What are the functions of the gag, pol, and env genes?

Answer 14

Group specific antigen gene: capsid, nucleocapsid, matrix, protease
Polymerase gene: RT, integrase
Env: encodes the envelope GlycoProteins— gp120, gp41

Question 15

What are the HIV regulatory genes?

Answer 15

Tat, rev, nef, vif, vpr, Vpu

- control the ability of HIV to infect a cell, produce new copies of the virus, or cause disease

Question 16

What converts RNA genome into a dsDNA genome?

Answer 16

RT

Question 17

How does RT work?

Answer 17

1. RT acts as an RDRP and synthesizes the complementary strand of DNA
2. RT acts as RNase and degrades the RNA strand
3. DNA dependent DNA POL reads the DNA template, and makes dsDNA
4. Results in dsDNA that is slightly longer than the original RNA

Question 18

What is the best target for the RT enzyme for an anti-viral therapy?

Answer 18

RDRP

Question 19

Where does the RT step (RNA to DNA) happen? Why can’t this happen until the virus enters the host cell?

Answer 19

In the virus’ core in the cytoplasm; there is no source of nucleotides without being in the host cell

Question 20

What is the function of gp120?

Answer 20

Docking glycoprotein

Question 21

What is the function of gp41?

Answer 21

Transmembrane glycoprotein

Question 22

What is the first step in the HIV genome replication cycle?

Answer 22

RT transcribes the RNA genome into dsDNA, and it is integrated into the host cell DNA

Question 23

What are the three activities of the RT enzyme?

Answer 23

1. RNA dependent DNA polymerase
2. RNase H
3. DNA dependent DNA polymerase

Question 24

How does HIV attach to the host cell?

Answer 24

• HIV binds to receptor CD4 with gp120, and this triggers a conformational change in gp120 and allows it to bind to the co-receptor, either CCR5 or CXCR4
• triggers conformational change in gp41 and results in a fusion peptide inserting in the cell membrane and fuses with the cell membrane

Question 25

What is the mutation that causes HIV resistance?

Answer 25

CCR5-Δ32

Question 26

What are the packaged tRNAs for?

Answer 26

A primer for reverse transcription

Question 27

What transcribes the integrated virus dsDNA genome?

Answer 27

Host cell RNA polymerase

Question 28

Can there be damage to the host cell when HIV is integrated?

Answer 28

It depends on if it is integrated in a gene or regulatory sequences

Question 29

What are the steps of HIV genome integration?

Answer 29

1. Recognition of the target site by the integrase
2. Staggered cutting of host cell DNA at target site, making short stretches of ssDNA
3. Ligating DNA into host cell DNA
4. Repair of ssDNA resulting in duplication of target

Question 30

What proteins does Gag produce?

Answer 30

NC (nucleocapsid), CA (core), MA (matrix), PR (protease)

Question 31

What proteins does Pol make?

Answer 31

RT and IN

Question 32

What proteins does env make?

Answer 32

Gp120 and 140

Question 33

How does HIV transcribe Gag AND Pol?

Answer 33

Ribosome frameshift— skips over the gag stop codon by shifting 1 nucleotide back at the slippery sequence towards the 5’ end

Question 34

When does HIV virus maturation happen? What does it look like?

Answer 34

Gag and Gag-Pol are still intact and the RT and IN are non functional; after the virus egresses