C5 CELL RECOGNITION AND THE IMMUNE SYSTEM

Question 1

Describe the structure of the human immunodeficiency virus (HIV)

Answer 1

1. RNA (as genetic material)
2. Reverse transcriptase
3. (Protein) capsid
4. Lipid envelope
5. Attachment proteins

Question 2

Differences between active and passive immunity?

Answer 2

1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells / memory cells;
3. Passive involves antibody introduced into body from outside / named source;
4. Active long term, because antibody produced in response to antigen;
5. Passive short term, because antibody (given) is broken down;
6. Active (can) take time to develop / work, passive fast acting.

Question 3

Describe how pathogens are destroyed by phagocytes.

Answer 3

1. Chemicals released by the pathogen that attracts the phagocyte
2. Phagocyte has receptors that attach to the pathogen
3. Phagocyte then engulfs the bacteria to form a phagosome
4. Lysosome fuses with the phagosome, then releases lysozymes that destroy bacteria by hydrolysing thier cell walls into it

[5. The soluble products of the hydrolysed pathogen is then absorbed into the cytoplasm of the phagocyte]

Question 4

Explain why HIV showing a lot of antigenic variability means that a vaccine might not be effective against HIV.

Answer 4

1. Antigen on HIV changes
2. Specific antibody / receptor no longer binds to the new antigen

OR

1.Many different strains of HIV / many antigens present on HIV
2.So Not possible to make a vaccine for all antigens / vaccine may not stimulate an antibody for a particular antigen;

Question 5

Explain why HIV rapidly entering host cells means that a vaccine might not be effective against HIV.

Answer 5

1. HIV enters cells before antibodies can bind to / destroy it
2. So antibodies cannot enter cells (to destroy HIV) / stay in blood

OR

1. Vaccine taken up too quickly to cause immune response
2. So no antibodies / memory cells formed;