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HIV

Biology: IB Diploma Higher Level, topic 11.2.6

Structure

Human immunodeficiency virus (HIV) is a virus that inhibits the immune system. The structure of HIV is:

Capsid

Capsid

  • Inside the centre of the HIV virus is a protein called the capsid.
  • The capsid contains the genetic material and enzymes.
RNA

RNA

  • The genetic material for HIV consists of two strands of single-stranded RNA.
  • The RNA is inside the capsid.
Enzymes

Enzymes

  • The enzymes inside the capsid include reverse transcriptase and integrase.
  • Reverse transcriptase and integrase are important to the role of HIV in infection.
Viral envelope

Viral envelope

  • The capsid is enclosed by a viral envelope.
  • The viral envelope has glycoproteins on its surface.
  • The glycoproteins bind to the cell surface membrane of TH cells to infect the cells.

Replication

HIV infects the immune system by replicating inside the T helper (TH) cells. The steps involved in this process are:

1) Bind to TH cells

1) Bind to TH cells

  • The glycoproteins on the surface of HIV binds to receptor proteins on the cell surface membrane of TH cells.
2) Release of the capsid

2) Release of the capsid

  • The capsid is injected into the TH cells.
  • The RNA and enzymes (reverse transcriptase and integrase) are released from the capsid.
3) Reverse transcriptase

3) Reverse transcriptase

  • Reverse transcriptase is an enzyme that converts the single-stranded RNA from the HIV into double-stranded DNA.
  • The DNA moves into the nucleus of the TH cells.
4) Integrase

4) Integrase

  • Integrase is an enzyme that inserts the HIV DNA into the TH cells DNA.
5) Expression

5) Expression

  • The genes in the HIV DNA are expressed in the TH cells.
  • The HIV proteins are synthesised and new HIV RNA is made.
6) Release of HIV

6) Release of HIV

  • New HIV viruses are released from the TH cells.
  • The TH cells die.
  • The HIV viruses can infect more cells.

AIDs

Acquired immune deficiency syndrome (AIDs) is a condition that is caused by HIV infection.

Cause

Cause

  • When an HIV virus infects a TH cell and replicates, the cells are killed.
  • As HIV spreads through the body and more TH cells are killed, the immune system weakens.
  • The weak immune system makes the individual highly susceptible to infection by other pathogens. This is AIDs.
Symptoms

Symptoms

  • Initial symptoms of HIV are similar to flu (chills and fever). The symptoms are seen within four weeks of infection.
  • As the immune system is weakened, individuals will be more vulnerable to infections (e.g. tuberculosis).
  • Eventually, AIDs sufferers may die from one of these infections.
  • AIDs can take a very long time to develop (up to 10 years).
Treating HIV

Treating HIV

  • HIV is a virus so it cannot be treated with antibiotics.
  • Antibiotics specifically target the enzymes and ribosomes in bacteria.
  • Antibiotics cannot be designed to target the enzymes in viruses because viruses use the host enzymes and ribosomes to replicate.
Potential treatment

Potential treatment

  • Treating HIV is difficult because it is a virus.
  • HIV has some virus-specific enzymes (e.g. reverse transcriptase).
  • Antiviral drugs can be designed to target the reverse transcriptase enzyme.

Test yourself on HIV

  • What two enzymes are inside the capsid of HIV?

  • What is the genetic material in HIV?

  • Which of the following statements about HIV are true?

  • Steps Involved in Replication of HIV

  • Which of these is NOT released from the capsid into the TH cells?

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