Immunology

Question 1

How do pathogens cause disease ?

Answer 1

Toxins enter cells and damage them
Entering a host cell and destroying it

Question 2

What are T cells and what do they do ?

Answer 2

Helper - Activates B cells
Cytotoxic - Destroys harmful antigens

Antigen receptor molecules

Question 3

What is an antigen ?

Answer 3

Foreign protein that causes an immune response

Question 4

What is an antibody ?

Answer 4

Protein made by a B lymphocyte in a response to an antigen

Question 5

What is the non specific response / phagocytosis ?

Answer 5

1 : Pathogen produces chemicals -> Phagocyte attracted and moves towards along concentration gradient
2 : Receptors on phagocyte attach to antigens on pathogen surface
3: Phagocyte engulfs pathogen into a Phagosome (vesicle)
4 : Lysosomes in phagosome fuse -> releases lysozymes which hydrolyse cell wall and digest bacteria
5 : Hydrolysis products absorbed into cytoplasm -> phagocyte becomes pathogen presenting -> activates T and B cells

Question 6

What is the cell mediated response (cytotoxic T cells) ?

Answer 6

Cytotoxic T cell produces protein that makes holes in membrane.
Lots of water moves in by osmosis -> Cell bursts

Question 7

What is the B cell response ?

Answer 7

B cell activated by Helper T cells
B cell binds to antigen presenting cell
B cells divide by mitosis -> produce clones
They become memory cells -> secrete antibodies that remain in blood

Question 8

What is the structure of an antibody ?

Answer 8

2 heavy chains attached together by a disulphide bridge
Light chains then bonded to the heavy chains
Variable region at the end of the 4 chains, antigen can attach here

Question 9

What is active immunity ?

Answer 9

Antigen triggers the production of memory cells, long term protection

Question 10

What is passive immunity ?

Answer 10

No memory cells produced, short term protection

Question 11

What are examples of active and passive immunity ?

Answer 11

a : common cold, the flu

p : snake bite, foetus during pregnancy

Question 12

What are features of a successful vaccine program ?

Answer 12

• cheap
• few side effects
• herd immunity
• easily stored

Question 13

What is a vaccine ?

Answer 13

Inactive/dead form of the pathogen inserted into blood

Question 14

What are monoclonal antibodies ?

Answer 14

Antibodies produced from the same B cell that bind to antigen

Question 15

Why is HIV difficult to vaccinate ?

Answer 15

Genetic mutations are common and they produce a different antigen, which memory cells can’t recognise

Question 16

What is the structure of HIV ?

Answer 16

Viral DNA contained in a protein capsid
reverse transcriptase with attachment proteins

Question 17

How does HIV replicate ?

Answer 17

• Attatchment protein attatches to receptor on helper T cell -> capsid released into cell and releases RNA into cytoplasm
• Reverse transcriptase makes complementary strand of DNA using viral RNA as template.
• Double stranded DNA inserted into regular DNA-> host cell enzymes make proteins from viral DNA
• Viral proteins assembled into new viruses -> infect other cells.

Question 18

How does a pregnancy test work ?

Answer 18

• Pregnant urine contains hCG hormone
• First antibody complementary to hCG hormone with dye
• Second antibody complementary to hCG hormone
• Third antibody complementary to first antibody

Question 19

How does the ELISA test work ?

Answer 19

1 : Antibodies bind with antigen at bottom of beaker
2 : Washed -> Blood plasma sample added
3 : Washed -> Second antibody only binds to primary antibody if antigen present
4 : Washed -> Substrate added and enzyme forms ESC
Colour change means positive result