HIV

Question 1

Describe the replication of HIV in helper T cells

Answer 1

1. HIV infects T helper cells - HIV attachment protein attaches to a receptor on the helper T-cell membrane
2. Virus lipid envelope fuses with cell surface membrane and capsid released into cell which uncoats, releasing RNA and reverse transcriptase into cytoplasm
3. Viral DNA is made from viral RNA - Reverse transcriptase produces a complementary viral DNA strand from viral RNA template
   - Double stranded DNA is made from this (DNA polymerase)
4. Viral DNA integrated into host cell’s DNA (by enzyme integrase)
5. This remains latent for a long time in host cell until activated
6. Host cell enzymes used to make viral proteins from viral DNA (within human DNA) → viral proteins assembled with viral RNA to make a new virus
7. New virus bud from cell (taking some of cell surface membrane as envelope)
8. Eventually kills helper T cells
9. Most host cells are infected and process repeat

Question 2

Explain how HIV causes the symptoms of AIDS –
acquired immune deficiency syndrome

Answer 2

• Infects and kills helper T cells (host cell) as it multiplies rapidly
• T helper cells then can’t stimulate cytotoxic T cells, B cells and
  phagocytes → impaired immune response
• E.g. B plasma cells can’t secrete antibodies for agglutination and
  destruction of pathogens by phagocytosis
• Immune system deteriorates
• More susceptible to infections
• Diseases that wouldn’t cause serious problems in healthy
  immune system are deadly

Question 3

Explain why antibiotics are ineffective against viruses

Answer 3

• Antibiotics can’t enter human calls – but viruses exists in its host
  cell (they are acellular)
• Viruses don’t have own metabolic reactions e.g. ribosomes (use
  of the host cell’s) which antibiotics target
• If we did use them… act as a selection pressure + gene mutation
  = resistant strain of bacteria via natural selection → reducing
  effectiveness of antibiotics and waste money

Question 4

Structure of HIV virus

Answer 4

Use acronym CARRL

C= Capsid
A=Attachment protein
R=RNA
R=Reverse transcriptase
L=Lipid envelope