27. Retroviruses

Question 1

WHAT TYPE OF RETROVIRUS IS HIV?

Answer 1

HIV-1 and HIV-2 belong to Lentiviruses subfamily.
- has a cylindrical nucleocapsid characteristic of a Lentivirus as opposed to a centrally located nucleocapsid characteristic of HTLV.

Question 2

How many subfamilies of retroviruses?

Answer 2

There are 4 subfamilies of Retroviruses

• Oncovirinae (Divided into B, C, D)
• Lentivirinae
• Spumavirinae
• Endogenous Viruses

Question 3

differences between Oncovirinae and lentivirinae, HIV 1 and 2 fall into which group?

Answer 3

Lentivirinae - cylindrical nucleocapsid (HIV, causes AIDS)

Oncovirinae - centrally located nucleocapsid (HTLV, causes Leukemia)

Question 4

Retroviruses

Answer 4

• single stranded RNA virus, enveloped.
• carries 2copies of a positive strand RNA = diploid
• uses reverse transcriptase (virus carries this around) to make DNA from RNA; DNA strand is integrated into host cell genome
• viral DNA is replicated with the host genome and passed down to future generations of cells through
  cell division

Question 5

HIV is transmitted either through

Answer 5

1. Sexual Activity
2. Exposure to Blood
3. Mother to Baby

Question 6

Two unique enzymes carried by retroviruses:

Answer 6

• reverse transcriptase

- integrase

Question 7

What enzyme allows retroviruses to integrate their genome into the host cell genome (after it’s made into dsDNA)?

Answer 7

Integrase (carried by viral genome).

Question 8

Steps in retrovirus infection of cell

Answer 8

1. viral +strand RNA made into DNA using rev transcriptase (RNA dependent DNA polymerase)
2. make complementary strand of DNA –> get dsDNA that can be inserted into host and replicated along host genome.
3. viral genome transcription and assembly of viral proteins into new viruses, which can bud through the plasma membrane and infect other cells. * Protease cleavage of gag proteins MUST occur after being enveloped.

Question 9

During retrovirus assembly, protease cleavage of ___ and ____ must occur after ____

Answer 9

• gag and gag-pol polypeptides

- being enveloped.

Question 10

There are two types of retroviruses:

Answer 10

a. Simple retroviruses encode only a few essential genes
b. Complex retroviruses such as the HIV virus encode a whole bunch of genes including the
accessory genes for HIV

Question 11

___ protein helps anchor HIV to CD4 T cells.

Answer 11

gp120

Question 12

What hooks gp120 to the rest of the virus?

Answer 12

a protein called gp41 hooks gp120 to the rest of the virus.

Question 13

When gp120 binds to a ____, conformational changes occur which allow ____ to pop out and assist the virus in fusing with the cell.

Answer 13

When gp120 binds to a CD4 molecule, conformational changes occur, which allow gp41 to pop out and assist the virus in fusing with the cell.

Question 14

3 of the HIV genes we need to know:

Answer 14

• gal (makes capsid protein)
• pol (makes polymerase, reverse transcriptase, and integrase)
• env (makes the envelope proteins including gp120)

Question 15

Kaposi’s Sarcoma is caused by ____, and usually found together with ___, why?

Answer 15

caused by HHV8, usually found with AIDS, bc it’s an opportunistic infection.

Question 16

Kaposi’s Sarcoma is more common in 2 populations:

Answer 16

Mediterranean decent and Ashkanazi Jews (more severe form of the disease than in Europeans).

Question 17

Trofile Assay

Answer 17

Tells you if your virus binds to coreceptor CCXR4, CCR5 or both.

Question 18

Viruses that bind to only ____ are called X4 or R4.
Viruses that bind to only ____are called R5.
Viruses that bind to both are called ___ or ____

Answer 18

Viruses that bind to only CXCR4 are called X4 or R4.
Viruses that bind to only CCR5 are called R5.
Viruses that bind to both are called X4R5 or R4R5.

Question 19

gp120 on HIV binds to which co-receptors/chemokine receptors on the CD4 T cells?

Answer 19

CCXR4 and CCR5.

Question 20

HIV-1 is very similar to ___, HIV-2 is very similar to ____.

Answer 20

HIV-1 = SIVcpz (chimpanzee-- simian immunodeficiency virus) 
HIV-2 = \_\_\_ (sooty mangabeys, monkeys --

Question 21

What is a provirus?

Answer 21

DNA intermediate of the retrovirus genome once it is integrated into the host.

Question 22

__ gene encodes for capsid protein of retroviruses

Answer 22

gag

Question 23

Pol gene encodes for ___

Answer 23

• polymerase
• reverse transcriptase
• integrase

Question 24

simple retroviruses encode for which 3 essential genes?

Answer 24

gag, pol, env

Question 25

Retrovirus genome

Answer 25

• two copies of POSITIVE-strand RNA genomes within a capsid.
• carries reverse transcriptase and integrase

Question 26

env gene encodes for ___

Answer 26

envelop proteins, including gp120

Question 27

Simple vs. complex retroviruses

Answer 27

simple retros only carry the 3 essential genes (gag,pol, env), complex retros encode for other accessory proteins.

Question 28

how is glycoprotein 120 involved in attachment and entrance of HIV into the host cell?

Answer 28

• gp120 anchors HIV to CD4 molecule on helper T cell.
• once gp120 binds to CD4, conformational changes allows gp120 to bind to co-receptors (CCXR4, CCR5).
• virus can then enter the cell via fusion.

Question 29

4 groups of retroviruses

Answer 29

Oncoviridae – centrally located nucleocapsid core in mature virion. (HTLV-1,2,5)
Lentivirinae – cylindrical nuclocapsid core (HIV-1, HIV-2).
Spurnavirane
Endogenous viruses

Question 30

lytic vs. latent infection of HIV, in which cell type?

Answer 30

lytic+latent = CD4 T cells 
latent = monocyte/macrophage family.

Question 31

diagnostic tests for HIV

Answer 31

ELIZA – antibody to GP120

Western Blot after ELIZA to confirm HIV.

Question 32

truvada

Answer 32

preexposure to HIV

Question 33

Outcomes of HIV infection

Answer 33

immunodeficiency and AIDS dementia.

Question 34

what allows the mutant HIV strain (vs. wildtype) to take over?

Answer 34

Dec in CD4 T cell allows mutant virus to replicate and inc.