Lesson 50 - HIV and AIDS

Question 1

When might vaccines not work?

Answer 1

• Certain individuals with defective immune systems, they may either not develop immunity or may develop the disease
• Individuals may have objections against vaccines - religious, ethical or medical reasons
• When pathogens mutate frequently - therefore it’s difficult to develop a vaccine against them

Question 2

Describe the structure of HIV?

Answer 2

Attachment proteins
Capsid
Lipid envelope
Genetic material (RNA)
Matrix
Reverse transcriptase (enzyme)

Question 3

How is HIV replicated? (5 marks)

Answer 3

1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
2. Nucleic acid/RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral protein/capsid/enzymes produced;
5. Virus (particles) assembled and released (from cell);

Question 4

Why is HIV a retrovirus?

Answer 4

It’s able to insert its genetic material into the host cell’s DNA using an enzyme called Reverse Transcriptase

Question 5

How can HIV lead to aids? (5 marks)

Answer 5

1. HIV replicates in and destroys T helper cells;
2. Leads to a decrease in number of T helper cells;
3. So fewer T helper cells can activate B cells;
4. So less plasma and memory cells formed;
5. So less/no antibodies against pathogens (secondary infections);
6. So immune system is unable to fight secondary infections;

Question 6

What is the normal amount of T-cell per mm3, and how much is found in AIDS patients?

Answer 6

Uninfected person: 800-1200 helper T cells in each mm³ of blood
Infected person: 200 T-cells/mm³ (critical value) So they become more susceptible to other infections due to an inadequate immune response

Question 7

What are the symptoms in the initial and late stages of AIDS?

Answer 7

Initial: Minor infections of mucous membranes (e.g. nose, ears, genitals) and recurring respiratory infections.
As AIDS progresses: Number of immune system cells further decreases. Patients become more susceptible to more serious infections, chronic diarrhoea, severe bacterial infections and tuberculosis.
Late stages: Very low number of immune system cells, and can develop a range of serious infections: toxoplasmosis of the brain, and candidiasis of the respiratory system.