Lecture 24 - HIV

Question 1

What type of genome do HIV viruses have?

Answer 1

(+)ssRNA

Question 2

What is the key enzyme only retroviruses have?

Answer 2

reverse transcriptase

Question 3

What is the primer for reverse transcriptase?

Answer 3

DNA or RNA

Question 4

What must the primer have in order for reverse transcriptase to work?

Answer 4

free 3’ OH group

Question 5

What is the template for reverse transcriptase?

Answer 5

RNA

Question 6

What does reverse transcriptase incorporate when synthesizing?

Answer 6

dNTP’s

Question 7

What is the activity of the RNase H in reverse transcriptase?

Answer 7

acts as helicase; destroys RNA

Question 8

What are 2 characteristics on DNA synthesis of reverse transcriptase?

Answer 8

error-prone and slow

Question 9

Why does reverse transcriptase have a high rate of mutation for HIV?

Answer 9

reverse transcriptase has no proofreading abilities

Question 10

What are the 2 glycoproteins on HIV’s envelope/capsid?

Answer 10

gp120 and gp41

Question 11

What are the receptor and 2 co-receptors for HIV?

Answer 11

CD4 (receptor) | coreceptors: CCR5 and CXCR4

Question 12

How many copies of genome is in each HIV virion?

Answer 12

2

Question 13

What host cell item is bound/hybridized to the HIV genome in the virion?

Answer 13

tRNA

Question 14

What do the ends of the HIV genome contain?

Answer 14

repeat sequences

Question 15

What are the 3 significant retroviral genes within the HIV genome?

Answer 15

gag, pol, env

Question 16

What does the “gag” gene encode for?

Answer 16

matrix and nucleocapsid proteins

Question 17

What does the “pol” gene encode for?

Answer 17

protease, polymerase, integrase

Question 18

What does the “env” gene encode for?

Answer 18

envelope proteins – gp120 and gp41

Question 19

What is HIV entry into cells accomplished by?

Answer 19

binding to CD4 receptors on host cell surfaces

Question 20

Which cells contain CD4 receptors on their surfaces?

Answer 20

macrophages and T-cells

Question 21

Which co-receptors are on T-cells and on macrophages respectively?

Answer 21

T-cell = CXCR4 | macrophages = CCR5

Question 22

In which stages of infection does HIV infect T-cells and macrophages respectively?

Answer 22

macrophages = EARLY | T-cell = LATER

Question 23

Why are macrophages infected by HIV early on in the infection?

Answer 23

macrophages are mostly in mucosal surfaces = initial sites of infection

Question 24

What type of receptor is CXCR4?

Answer 24

G-protein coupled receptor

Question 25

When is the HIV fusion peptide exposed?

Answer 25

when gp120 and gp41 bind/fuse with CD4 and coreceptor

Question 26

What does the process of reverse transcription promote?

Answer 26

genetic recombination

Question 27

HIV has 2 copies of its genome, how is this used in genetic recombination?

Answer 27

can choose either genome | if one = mutated, other is used | end up with dsDNA molecule

Question 28

What are the 4 catalytic activities that occur during reverse transcription?

Answer 28

RNA-directed polymerization | DNA-directed polymerization | DNA unwinding | RNA hydrolysis (degradation) in RNA-DNA hybrids

Question 29

What is the function of tRNA hybridized/bound to HIV genome?

Answer 29

used as a primer

Question 30

Is the reverse transcription event of HIV genome a circular or linear one?

Answer 30

circular

Question 31

What are the 5 highlights of the conversion of ssRNA HIV genome to dsDNA?

Answer 31

DNA and RNA = primers | DNA and RNA = templates | reverse transcription of one RNA results in dsDNA | dsDNA has long terminal repeats | dsDNA serve as proviral DNA, integrated into host chromosomes as provirus

Question 32

Where does reverse transcription occur?

Answer 32

cytoplasm in the virion

Question 33

What are the 3 steps of integration of HIV proviral DNA?

Answer 33

processing, joining, repair

Question 34

What is the “processing” step of integration of HIV proviral DNA?

Answer 34

endonucleolytic nicking occurs to form new 3’OH end

Question 35

What is the “joining” step of integration of HIV proviral DNA?

Answer 35

retroviral DNA = joined to target DNA

Question 36

What is the “repair” step of integration of HIV proviral DNA?

Answer 36

accomplished by host cell repair process

Question 37

What replicates the HIV proviral DNA?

Answer 37

host RNA polymerase via transcribing it

Question 38

What phase of gene expression are gag, pol, and env expressed?

Answer 38

late phase

Question 39

During the HIV life cycle, what genomes are replicated?

Answer 39

NONE!!! They are all transcribed (ssRNA) or reverse-transcribed (dsDNA)