[W11] Retroviruses

Question 1

What is the genome type of retroviruses?

Answer 1

Diploid, single-stranded, positive-sense RNA.

Question 2

What enzyme do retroviruses use to convert RNA to DNA?

Answer 2

Reverse transcriptase.

Question 3

What makes retroviruses unique among RNA viruses?

Answer 3

They replicate via a DNA intermediate and use host RNA polymerase II.

Question 4

What is the relationship between retroviruses and retrotransposons?

Answer 4

Retroviruses evolved from LTR retrotransposons by acquiring an env gene.

Question 5

What percent of the human genome is derived from endogenous retroviruses (ERVs)?

Answer 5

About 8%.

Question 6

What animal viruses did HIV-1 and HIV-2 originate from?

Answer 6

HIV-1: chimpanzee SIV; HIV-2: sooty mangabey SIV.

Question 7

What are the main genes in a simple retrovirus genome?

Answer 7

gag, pol, env (flanked by LTRs).

Question 8

What additional genes are found in lentiviruses like HIV?

Answer 8

vif, vpr, vpu, tat, rev, nef.

Question 9

What proteins are encoded by gag?

Answer 9

Matrix, capsid, and nucleocapsid proteins.

Question 10

What does the pol gene encode?

Answer 10

Protease, reverse transcriptase, and integrase.

Question 11

What does the env gene encode?

Answer 11

gp120 (surface) and gp41 (transmembrane) envelope proteins.

Question 12

What receptor does HIV use for cell entry?

Answer 12

CD4 and a co-receptor (CCR5 or CXCR4).

Question 13

What viral protein facilitates HIV fusion with host membrane?

Answer 13

gp41.

Question 14

What is the function of reverse transcriptase?

Answer 14

Synthesizes DNA from RNA and degrades RNA using its RNase H activity.

Question 15

What serves as a primer for reverse transcription in retroviruses?

Answer 15

A host tRNA.

Question 16

What is the provirus?

Answer 16

The integrated viral DNA within the host genome.

Question 17

What enzyme integrates retroviral DNA into the host genome?

Answer 17

Integrase.

Question 18

How are HIV mRNAs produced?

Answer 18

By host RNA polymerase II from the integrated provirus.

Question 19

What is the role of unspliced HIV RNA?

Answer 19

Encodes Gag and Pol and is packaged into virions.

Question 20

What regulatory mechanism allows production of Pol from the same RNA as Gag?

Answer 20

Ribosomal frameshifting.

Question 21

What does the Psi (Ψ) packaging signal do?

Answer 21

Ensures the RNA genome is packaged into new virions.

Question 22

How are retroviral glycoproteins processed?

Answer 22

Translated in the ER, glycosylated, then trafficked to the plasma membrane.

Question 23

What complex is involved in HIV budding?

Answer 23

The ESCRT (endosomal sorting complex required for transport).

Question 24

When does retroviral maturation occur?

Answer 24

After budding, through cleavage by HIV protease.

Question 25

Why does HIV mutate rapidly?

Answer 25

Reverse transcriptase lacks proofreading, resulting in high error rates.

Question 26

What are quasispecies in the context of HIV?

Answer 26

A diverse population of virus variants within one individual.

Question 27

What allows genetic recombination in HIV?

Answer 27

The diploid genome and template switching during reverse transcription.

Question 28

What immune cells are infected by HIV?

Answer 28

CD4+ T cells and macrophages.

Question 29

What protein helps HIV evade cytotoxic T lymphocytes (CTLs)?

Answer 29

Nef, by downregulating MHC class I.

Question 30

What is the role of Tat in HIV?

Answer 30

Enhances transcription elongation from the viral LTR.

Question 31

What is Rev's function?

Answer 31

Facilitates export of unspliced and singly spliced mRNAs from the nucleus.

Question 32

What is the typical progression of untreated HIV infection?

Answer 32

Acute infection → chronic latency → AIDS.

Question 33

What is the CD4+ T cell threshold for AIDS diagnosis?

Answer 33

Below 200 cells/mm³.

Question 34

Name three common opportunistic infections in AIDS.

Answer 34

Pneumocystis jirovecii pneumonia, Kaposi's sarcoma, candidiasis.

Question 35

What are the main methods for HIV diagnosis?

Answer 35

ELISA, Western blot, RT-PCR.

Question 36

What cells initiate HIV transmission during sexual contact?

Answer 36

Langerhans' cells.

Question 37

What factors increase the risk of HIV acquisition?

Answer 37

Uncircumcised status, STIs, high viral load in donor.

Question 38

How is HIV transmitted from mother to child?

Answer 38

In utero, during delivery, or via breastfeeding.

Question 39

What is the global burden of HIV (as of 2019–2020)?

Answer 39

38 million living with HIV; 690,000 deaths/year.

Question 40

What is HAART?

Answer 40

Highly active antiretroviral therapy – a combination of at least 3 drugs from different classes.

Question 41

How do NRTIs work?

Answer 41

Incorporated by RT into viral DNA, causing chain termination.

Question 42

How do NNRTIs work?

Answer 42

Bind to a non-active site of RT, altering its shape and function.

Question 43

What do protease inhibitors do?

Answer 43

Prevent maturation by blocking cleavage of Gag-Pol polyproteins.

Question 44

What is Maraviroc and how does it work?

Answer 44

A CCR5 antagonist that blocks HIV entry by preventing coreceptor binding.

Question 45

What is Enfuvirtide and what does it block?

Answer 45

A fusion inhibitor that binds gp41 and blocks membrane fusion.

Question 46

What is the role of integrase inhibitors like Raltegravir?

Answer 46

Prevent integration of viral DNA into host genome.

Question 47

Why is developing an HIV vaccine challenging?

Answer 47

High mutation rate and glycan shielding on gp120 mask antigenic sites.

Question 48

What are some strategies to prevent HIV transmission?

Answer 48

Safe sex, blood screening, clean needles, mother-to-child transmission prevention, PrEP.