Question

HIV is a retrovirus (a virus that uses reverse transcriptase).

a. What is reverse transcriptase?

b. How is a retrovirus different from other viruses?

c. How does a retrovirus infect a cell and reproduce itself?

2. Review of the immune system.

a. What is a T cell?

b. What varieties of T cell exist? How are they functionally different?

c. What are their roles in the human body?

d. How is each T cell variety differentiated from the others (molecularly)?

3. Immune system and HIV

a. Which type(s) of immune cells is/are targeted by HIV?

b. Why are other cells not targeted by the virus?

c. How should cytotoxic T cells respond to the initial phase of HIV infection (when some T helper cells are still functioning)? Explain your reasoning.

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d. As time progresses, why do the cytotoxic T cells stop responding to the HIV infection?

Propose an explanation.

e. What happens to the immune system after HIV infection? Why? Can this account for the symptoms of AIDS (i.e., immunodeficiency, or the inability to defend against any foreign invaders like viruses and bacteria)?

f. Why do you suppose that there is a delay between the time of HIV infection and the appearance of symptoms (and AIDS)?

g. How does HIV evade the immune system?

4. HIVprotection

a. Consider how HIV infects cells and reproduces. Also consider how the immune system fights off

HIV infection. Humans differ by having mutations that result in slightly different proteins and immune function. Suggest as many hypotheses as possible to explain why some individuals might be protected against HIV infection. In other words, where and how might new viral infections be stopped? What could be different about the people who seem protected against HIV that caused viral replication to stop? Come up with at least three possibilities.

Answer 1

Ans) a) A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. In retroviruses and retrotransposons, this cDNA can then integrate into the host genome, from which new RNA copies can be made via host-cell transcription.

b) There are many technical differences between viruses and retroviruses. But generally, the main difference between the two is how they replicate within a host cell.

Here’s a look at the steps of the life cycle of human immunodeficiency virus (HIV) to help illustrate how retroviruses replicate:

Attachment- The virus binds to a receptor on the surface of the host cell. In the case of HIV, this receptor is found on the surface of immune cells called CD4 T cells.
Entry- The envelope surrounding the HIV particle fuses with the membrane of the host cell, allowing the virus to enter the cell.
Reverse transcription. HIV uses its reverse transcriptase enzyme to turn its RNA genetic material into DNA. This makes it compatible with the host cell’s genetic material, which is vital for the next step of the life cycle.
Genome integration. The newly synthesized viral DNA travels to the cell’s control center, the nucleus. Here, a special viral enzyme called integrase is used to insert the viral DNA into the host cell’s DNA.
Replication- Once its DNA has been inserted to the host cell’s genome, the virus uses the host cell’s machinery to produce new viral components, such as viral RNA and viral proteins.
Assembly- The newly made viral components combine close to the cell surface and begin to form new HIV particles.
Release- The new HIV particles push out from the surface of the host cell, forming a mature HIV particle with the help of another viral enzyme called protease. Once outside the host cell, these new HIV particles can go on to infect other CD4 T cells.
The key steps that differentiate retroviruses from viruses are reverse transcription and genome integration.

c) Retroviruses also have the enzyme reverse transcriptase, which allow it to copy RNA into DNA and use tkaat DNA "copy" to infect human, or host, cells. .mThen the viral RNA is converted into DNA and the virus uses the host cell's machinery to replicate itself during a process called reverse transcription.