HIV

Question 1

Describe how HIV is replicated after it has entered a human cell.

Answer 1

Reverse transcriptase;

Accept integrase/description of action of

Enzyme uses (HIV) RNA to make DNA (copy);

DNA joined to (host) cell’s DNA/chromosome;

DNA used to make HIV RNA (copies);

Accept (HIV) DNA replicated when (T) cell divides

And HIV capsid proteins/enzymes;

Made at (host) ribosomes;

Assembly of new virus particles;

Budding off from membrane (of host cell);

Question 2

People with AIDS die because they are unable to produce an immune response to pathogens (lines 2-4).

Explain why this leads to death.

Answer 2

Infected by / susceptible to (other) pathogen(s) / named disease caused by a pathogen (from environment);

Context is where immune system cannot prevent or stop these events

Allow attack / kill

2. Pathogen(s) reproduce / cause diease (in host);

MPs not given in context of HIV

3. Damage cells / tissues / organs;
4. Release toxins;

Question 3

Explain why each of the following means that a vaccine might not be effective against HIV.

(i) HIV rapidly enters host cells

Answer 3

(HIV enters cells) before antibodies can bind to / destroy it;

Ignore SAFETY comments

1. and 2. Relate to antibodies
2. Antibodies cannot enter cells (to destroy HIV) / stay in blood;

Vaccine taken up too quickly to cause immune response;

5. and 6. Relate to vaccine
6. So no antibodies / memory cells formed;

Question 4

Explain why each of the following means that a vaccine might not be effective against HIV.

Answer 4

Antigen (on HIV) changes;

Accept mutates

2. (Specific) antibody / receptor no longer binds to (new) antigen;

Ignore SAFETY comments

Many different strains of HIV / many antigens present on HIV;

4. Not possible to make a vaccine for all antigens / vaccine may not stimulate an antibody for a particular antigen;

Question 5

So far, these types of vaccine have not been considered safe to use in a HIV mass vaccination programme (lines 14-15).

Suggest why they have not been considered safe.

Answer 5

Inactive virus may become active / viral transformation;

2. Attenuated virus might become harmful;
3. Non-pathogenic virus may mutate and harm cells;
4. Genetic information / protein (from HIV) may harm cells;
5. People (may) become / test HIV positive after vaccine used;

Question 6

The destruction of T-cells by HIV leads to the death of an infected person.
Explain how.

Answer 6

Not enough/no T-cells to activate B-cells/lead to antibody production/
activate immune system;

Accept death of T-cells weakens the immune system

Person unable to fight /more prone to (opportunistic) infections/cancer;

Accept diseases

Example of infection/cancer;

Question 7

Describe how new viruses are produced after HIV has infected a T cell.

Answer 7

DNA copy made (of viral RNA);
Inserted into host DNA / chromosomes;
(Uses viral DNA to) make viral proteins/particles;
Makes viral RNA;
(Host) cell makes new viruses;
“Budding off” / wrapped in cell membrane;

Question 8

Explain why the number of HIV particles in the blood

(i) rises during the first few months after infection

remains low between 1 and 7 years after infection.

Answer 8

(HIV is) invading cells which make new viruses;

Cells release viruses into blood;

Virus remains dormant/exists as 

provirus/exists as DNA in host DNA;

Question 9

his person developed a large number of infections about 9 years after he first became infected with HIV. Using information from the graph, explain why.

Answer 9

HIV destroys T cells;
More (free) viruses produced leads to fall in T-cells;
(So fewer) T-cells activate B-cells/memory cells;

Reduced/no antibody production;
Immune system not working properly/inability to fight infection;
Opportunistic infections;