HIV

Question 1

Describe the structure of a HIV particle:

Answer 1

1. Lipid envelope.
2. RNA
   3 Reverse transcriptase
3. Capsid
4. Attachment protein

Question 2

Describe the replication of HIV in helper T cells

Answer 2

1. HIV attachment proteins attach to receptors on helper T cell 2. Lipid envelope fuses with cell-surface membrane, releasing capsid into cell 3. Capsid uncoats, releasing RNA and reverse transcriptase
2. Reverse transcriptase converts viral RNA to DNA
3. Viral DNA inserted / incorporated into helper T cell DNA (may remain latent) 6. Viral protein / capsid / enzymes are produced
   a. DNA transcribed into HIV mRNA
   b. HIV mRNA translated into new HIV proteins
4. Virus particles assembled and released from cell (via budding).

Question 3

Explain how HIV causes the symptoms of acquired immune deficiency syndrome (AIDS):

Answer 3

1. HIV infects and kills helper T cells (host cell) as it multiplies rapidly
   -So T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
   - So B plasma cells can’t release as many antibodies for agglutination & destruction of pathogens
2. Immune system deteriorates → more susceptible to (opportunistic) infections
3. Pathogens reproduce, release toxins and damage cells

Question 4

Explain why antibiotics are ineffective against viruses:

Answer 4

1. Viruses do not have structures / processes that antibiotics inhibit:
2. Viruses do not have metabolic processes (eg. do not make protein) / ribosomes
3. Viruses do not have bacterial enzymes / murein cell wall

Question 5

Explain how monoclonal antibodies can be used in medical diagnosis:

Answer 5

1. MCAB have a specific tertiary structure
2. Complementary to specific receptor.
3. Dye attached to antibody
4. Antibody binds to receptor, forming an antigen-antibody complex.

Question 6

Explain the use of antibodies in the ELISA test: direct ELISA

Answer 6

1. Attach sample with potential antigens to well
2. Add complementary monoclonal antibodies with enzymes attached → bind to antigens if present
3. Wash well → remove unbound antibodies (to prevent false positive)
4. Add substrate → enzymes create products that cause a colour change (positive result)

Question 7

Explain the use of antibodies in the ELISA test: sandwich ELISA

Answer 7

1. Attach specific MCAB to well.
2. Add sample with potential antigens, then wash well.
3. Add complementary MCABs with enzymes attached, bind to antigens if present.
4. Wash well, remove unbound antibodies, prevent false positive.
5. Add substrate, enzymes create products that cause a colour change.

Question 8

Explain the use of antibodies in the ELISA test to detect antibodies

Answer 8

1. Attach specific antigens to well.
2. Add sample with potential antibodies, then wash well.
3. Add complementary MCABs with enzymes attached, bind to antibodies if present.
4. Wash well, remove unbound antibodies, prevent false positive.
5. Add substrate, enzymes create products that cause a colour change.

Question 9

Suggest the purpose of a control well in the ELISA test

Answer 9

1. Compare to test to show only enzyme causes colour change.
2. Compare to show all unbound antibodies have been washed away.

Question 10

Suggest the purpose of a control well in the ELISA test:

Answer 10

1. Antibody with enzyme remains/washed out.
2. So substrate converted into colour product.

Question 11

Discuss some general ethical issues associated with the use of vaccines of MCABs:

Answer 11

1. Pre-clinical testing on animals, potential stress.
2. Animals not killed, reduces human suffering.
3. Clinical trials on humans, potential harm.
4. Vaccines, may continue high risk activities and still develop/ pass on pathogens.
5. Use of drug, potentially dangerous side effects.

Question 12

Suggest some points to consider when evaluating methodology relating to the use of vaccines and MCAB?

Answer 12

1. Was the sample size large enough to be representative?
2. Were participants diverse in terms of age, sex, ethnicity and health status?
3. Were placebo / control groups used for comparison?
4. Was the duration of the study long enough to show long-term effects?
   5 Was the trial double-blind (neither doctor / patient knew who was given drug or placebo) to reduce bias?

Question 13

Suggest some points to consider when evaluating evidence and data relating to the use of vaccines and monoclonal antibodies:

Answer 13

1. What side effects were observed, and how frequently did they occur?
2. Was a statistical test used to see if there was a significant difference between start & final results?
3. Was the standard deviation of final results large, showing some people did not benefit?
4. Did standard deviations of start & final results overlap, showing there may not be a significant difference?
5. What dosage was optimum? Does increasing dose increase effectiveness enough to justify extra cost?
6. Was the cost of production & distribution low enough?