Lecture 24 - HIV Flashcards
What type of genome do HIV viruses have?
(+)ssRNA
What is the key enzyme only retroviruses have?
reverse transcriptase
What is the primer for reverse transcriptase?
DNA or RNA
What must the primer have in order for reverse transcriptase to work?
free 3’ OH group
What is the template for reverse transcriptase?
RNA
What does reverse transcriptase incorporate when synthesizing?
dNTP’s
What is the activity of the RNase H in reverse transcriptase?
acts as helicase; destroys RNA
What are 2 characteristics on DNA synthesis of reverse transcriptase?
error-prone and slow
Why does reverse transcriptase have a high rate of mutation for HIV?
reverse transcriptase has no proofreading abilities
What are the 2 glycoproteins on HIV’s envelope/capsid?
gp120 and gp41
What are the receptor and 2 co-receptors for HIV?
CD4 (receptor) | coreceptors: CCR5 and CXCR4
How many copies of genome is in each HIV virion?
2
What host cell item is bound/hybridized to the HIV genome in the virion?
tRNA
What do the ends of the HIV genome contain?
repeat sequences
What are the 3 significant retroviral genes within the HIV genome?
gag, pol, env
What does the “gag” gene encode for?
matrix and nucleocapsid proteins
What does the “pol” gene encode for?
protease, polymerase, integrase
What does the “env” gene encode for?
envelope proteins – gp120 and gp41
What is HIV entry into cells accomplished by?
binding to CD4 receptors on host cell surfaces
Which cells contain CD4 receptors on their surfaces?
macrophages and T-cells
Which co-receptors are on T-cells and on macrophages respectively?
T-cell = CXCR4 | macrophages = CCR5
In which stages of infection does HIV infect T-cells and macrophages respectively?
macrophages = EARLY | T-cell = LATER
Why are macrophages infected by HIV early on in the infection?
macrophages are mostly in mucosal surfaces = initial sites of infection
What type of receptor is CXCR4?
G-protein coupled receptor
When is the HIV fusion peptide exposed?
when gp120 and gp41 bind/fuse with CD4 and coreceptor
What does the process of reverse transcription promote?
genetic recombination
HIV has 2 copies of its genome, how is this used in genetic recombination?
can choose either genome | if one = mutated, other is used | end up with dsDNA molecule
What are the 4 catalytic activities that occur during reverse transcription?
RNA-directed polymerization | DNA-directed polymerization | DNA unwinding | RNA hydrolysis (degradation) in RNA-DNA hybrids
What is the function of tRNA hybridized/bound to HIV genome?
used as a primer
Is the reverse transcription event of HIV genome a circular or linear one?
circular
What are the 5 highlights of the conversion of ssRNA HIV genome to dsDNA?
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
Where does reverse transcription occur?
cytoplasm in the virion
What are the 3 steps of integration of HIV proviral DNA?
processing, joining, repair
What is the “processing” step of integration of HIV proviral DNA?
endonucleolytic nicking occurs to form new 3’OH end
What is the “joining” step of integration of HIV proviral DNA?
retroviral DNA = joined to target DNA
What is the “repair” step of integration of HIV proviral DNA?
accomplished by host cell repair process
What replicates the HIV proviral DNA?
host RNA polymerase via transcribing it
What phase of gene expression are gag, pol, and env expressed?
late phase
During the HIV life cycle, what genomes are replicated?
NONE!!! They are all transcribed (ssRNA) or reverse-transcribed (dsDNA)
