Question

A) How does HIV bind to a host cell?

Answer 1

1. The correct answer is: The viral envelope proteins interact with CD4 and a co-receptor on the cell membrane.

Binding and entering the host cell are the first steps of the HIV virus infection. So, these steps play a major role in determining the ability of HIV to degrade the human immune system. Binding of HIV to CD4+ T lymphocytes (express chemokine receptors CCR5 and CXCR4 called co-receptors) triggers the fusion of the viral and host cell membranes, initiating infection (viral core gets into the cytoplasm).

Attachment of the virion can be:

• Nonspecific-envelop protein of the virus (Env) binds to cell-surface heparan sulfate proteoglycans

• Specific-Env binds to integrin.

2. The correct answer is: Activation of the host cell by cytokines, growth factors, or antigens.

After the viral capsid enters the cell, single-stranded RNA genome is released from the attached viral proteins and copied it into a complementary DNA (cDNA) molecule thanks to an enzyme called reverse transcriptase. Next step is the integration of the viral DNA into the host cell's genome. This process is done by another viral enzyme called integrase. The integrated DNA  is transcribed into RNA and then translated into proteins that will help the package of new viruse particles.

3. The answer is: false

Reverse transcriptase is an enzyme that catalyzes the formation of DNA from an RNA template. Since the genome of the virus (HIV) is single stranded RNA, reverse transcriptase copies it into a complementary DNA (cDNA) molecule. Thanks to this enzyme, formed cDNA can be integrated into host’s genome. Because of this proprety, antiretroviral drugs used to treat HIV infection work as reverse-transcriptase inhibitors.