9 - Disease and Immunity

Question 1

How do pathogens cause diease?

Answer 1

Damaging host cells

Releasing toxins

Question 2

What is an antigen?

Answer 2

A non-self protein that stimulates an immune response of antibodies

Question 3

Where are antigens found?

Answer 3

Can be on the surface of a cell or freely circulating in the blood (e.g. toxins)

Question 4

Describe the non-specific immune response

Answer 4

Phagocytosis - a phagocyte recognises and binds to antigen
Phagocyte engulfs pahtogen
Pathogen enclosed in vesicle
Lysosome fuse with vesicle
Lysosomes contain hydrolytic enzymes that damage bacterial cell walls
These diges the pathogen by hydrolysis

Question 5

What is an antigen presenting cell?

Answer 5

A phagocyte that places antigens from the pathogen onto it’s cell surface membrane

Question 6

Give examples of antigen presenting cells

Answer 6

Cells that are infected by a virus
Phagocyte that engulfed and hydrolysed a pahtogen
An abnormal cell e.g. cancerous cell

Question 7

Describe the cellular response

Answer 7

Antigen detected by receptor on specific T cell
Activates T cell to undergo mitosis to produce cytotoxic cells and memory cells and releases chemicals that active cytotoxic T cells, B cells and phagocytes
Cytotoxic T cells release perforins (proteins)

Question 8

Describe the secondary immune response

Answer 8

When same antigen encountered at later date memory cels:
Divide rapidly
Produce large numbers of memory and plasma cells, therefore more antibodies produced faster

Question 9

What is the function of plasma cells?

Answer 9

Produce and secrete antibodies

Question 10

What do B cells divide into?

Answer 10

Plasma cells and memory cells

Question 11

What does the humoral response involve?

Answer 11

B cells

Question 12

What does the cellular response invole?

Answer 12

T cells

Question 13

What do antibodies do?

Answer 13

React with antigens to form antigen-antibody complexes as theya re complementary shapes so antibodies are very specific

Question 14

Why does vaccination not eliminate a disease?

Answer 14

Defective immune system so vaccination fails to induce immunity
Pathogen may mutate and change antigen shape (antigenic variation)

Question 15

What are monoclonal antibodies?

Answer 15

Antibodies produced by B cells

All have the same tertiary structure and bind to one specific antigen

Question 16

What happens during the ELISA test?

Answer 16

Add specific monoclonal antibodies to a solution suspected of containing a certain antigen
Antibodies will bind to the antigen if present
Enzyme attached to second antibodies, if present at the end the substance changes colour

Question 17

Why is it important to wash after the second antibody is added? (ELISA)

Answer 17

To remove unbound 2nd antibody to prevent a false positive result

Question 18

What would happen if there were no antigens present in the sample?

Answer 18

Antibodies would not have bound and would be washed away

No enzyme present to hydrolyse substrate so no colour change

Question 19

How can the ELISA test detect the amount of antigen presesnt in a sample?

Answer 19

More antigens present, more antigen - antibody complexes formed so more enzyme substrate complexes so more coloured products

Question 20

How do viruses (e.g. HIV) replicate?

Answer 20

Enter blood stream
Attachment proteins bind to specific, complementary receptors on T cells
Capsid injected into cell
RNA and enzyme released into cell
Complimentary strand of DNA made using RNA as template

Question 21

What does the capsid in a virus contain?

Answer 21

RNA and enzyme (reverse transcriptase)

Question 22

What are the symptoms of AIDS?

Answer 22

Infection of the lungs, intestines, brain and eyes
Fever and tiredeness
Weight loss
Diarrhoea

Question 23

Why can’t antibiotics be used to treat viral infections?

Answer 23

Viruses do not posses structures targetted by drugs (e.e. cell walls or ribosomes)
Viruses have a different metabolism
Viruses infect body cells, so antibiotics cannot affect them without damaging the cell