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12.2.2.3.2. Life cycle of the AIDS virus

Life cycle of the AIDS virus (human immunodeficiency syndrome)

The viruses that cause AIDS in humans (HIV1 and HIV2) are from the group of retroviruses, having single-stranded RNA as their genetic material. Therefore, their genetic material can act as mRNA and form proteins in the cells they parasitize. For DNA synthesis, two copies of its RNA and the help of the reverse transcriptase enzyme are needed. 

  1. The HIV virus has proteins in its envelope that are attracted to receptors located on the membrane of a lymphocyte. When the virus binds to the receptor, other proteins in the membrane are activated that cause both membranes to fuse. This recognition is necessary for the virus to adhere to and enter the cell.
  2. After fusing, decapsidation occurs, leaving the virus RNA free in the cytoplasm. The viral enzyme reverse transcriptase will transcribe the RNA of the virus into a double strand of DNA. At this point, it is fairly easy for mutations to occur in HIV, since reverse transcriptase often makes mistakes when moving from viral RNA to DNA.
  3. HIV (proviral) DNA enters the nucleus of the infected cell.
  4. The integration of viral DNA into the cell's DNA occurs thanks to the intervention of an enzyme called integrase.
  5. RNA and proteins are produced from DNA that will allow the formation of new viruses. The provirus (viral DNA integrated into the DNA of the host cell) can be inactive for a long time without producing new copies of HIV (quiescent cells with latent virus).
  6. Assembly: New viruses are formed with RNA, proteins, and cell membrane.
  7. Budding: The newly assembled virus leaves the cell through the plasma membrane, surrounding itself with a fragment that will form its envelope.
  8. The newly formed virus is immature, and the action of another enzyme, the HIV protease, is necessary for it to mature and become infectious, transforming into a mature HIV.
  9. The AIDS virus (HIV) is a retrovirus, so its genetic material is RNA (and not DNA). In order to replicate within the host cell (T4 lymphocytes), the RNA molecule has to form double-stranded DNA with the help of the enzyme reverse transcriptase or reverse transcriptase. Once viral DNA is formed, it can form new viral particles through RNA and protein synthesis. If treatment with reverse transcriptase inhibitors is carried out, the replication of the virus is paralyzed and the viral load of the patient decreases.

By US National Institute of Health (redrawn by en:User:Carl Henderson) [Public domain], via Wikimedia Commons

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Aragon, June 2019, option A, question 4.

AIDS is caused by the HIV virus, whose genetic material is in the form of RNA. Explain the cycle of this virus. (2 points)

Aragon. September 2017, option B, question 5.

AIDS is a disease that affects humans. The cause is a virus that has its genetic material in the form of RNA. When this virus infects a cell, it can lie dormant for years. (2 points)

a. What type of reproductive cycle do you think this virus exhibits? Justify your answer. (1 point)

b. What is the name of the process that the RNA of the virus must follow to integrate into the DNA of the infected cell? Briefly explain what it consists of. (1 point)

Valencian Community, July 2017, option A, block 4, question 1.

HIV virions have RNA as their genetic material. However, when they infect a cell they make a copy of its RNA in the form of DNA (4 points).

a) What is this process called and what is the most important enzyme involved?

b) What is the importance of this process in the HIV cycle?

Asturias, June 2021, question 5B, part A

When a patient is detected with a disease caused by a retrovirus, they are treated with specific inhibitors of viral reverse transcriptase (reverse transcriptase) and, then, the amount of virus drops sharply.

a) Reasonably explain the basis for this effect. (Maximum score 1 point)


         

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