Cell recognition and the immune system

Question 1

Antigen

Answer 1

-molecules recognised as foreign by the immune system → can stimulate an immune response
-ofen proteins on the surface of cells → have a specific tertiary structure

Question 2

What do antigens allow the immune system to identify?

Answer 2

Pathogens
Cells from other organisms
Abnormal body cells
Toxins released from pathogens

Question 3

Describe the process of phagocytosis

Answer 3

1) phagocyte recognises the foreign antigens on the pathogen and binds to the antigen
2) phagocyte engulfs pathogen by surrounding it with its cell membrane
3) pathogen is contained in the vacuole of the phagocyte
4) lysosome fuses with the phagosome and releases lysozyme
5) these hydrolyse/destroy the pathogen
6) phagocyte becomes an antigen presenting cell and stimulates a specific immune response

Question 4

the cellular response (response of T lymphocytes to a foreign antigen)

Answer 4

1) T lymphocytes recognise antigen-presenting cells after phagocytosis

2) A specific T helper cell with a receptor complementary to the specific antigen binds to it → t helper cell becomes activated → divides rapidly by mitosis

a) stimulate into B-cells for the humoral response
b) stimulate cytotoxic T cells to kill infected cells by producing perforin
c) stimulate phagocytes to engulf pathogens by phagocytosis

Question 5

the humoral response (the response of B cells to a foreign antigen e.g. in blood)

Answer 5

1. Clonal selection
   a) specific B cell binds to antigen-presenting cell and is stimulated by T helper cells which release cytokines
   b) divides rapidly by mitosis
   to form clones (clonal expansion)
2. some become b-plasma cells for the primary immune response (secrete monoclonal antibody into the blood)
3. some become memory b-cells for the secondary immune repsonse

Question 5

Primary response

Answer 5

-produce antibodies at a slower and lower concentration because not many B cells are available to produce antibodies
-T helpers need to activate the B cells to make antibodies (takes time)
-so infected individuals will express symptoms

Question 6

Secondary response (role of memory cells)

Answer 6

-Produces antibodies faster and at a higher concentration because more B and T cells present
-B memory cells undergo mitosis quicker

Question 7

What’s the structure of an antibody and how does it relate to its function?

Answer 7

quaternary structure 4 polypeptide chains held together by hydrogen, ionic and disulfide bonds
-enables specific binding site to form which is a complementary shape to a specific antigen
-enables antigen-antibody complex to form

Question 8

how do antibodies work to destroy a pathogen?

Answer 8

binds 2 pathogens at a time at the binding site forming an antigen-antibody complex
-enables antibodies to clump up together (agglutination)

Question 9

what is a vaccination?

Answer 9

-injection of antigens
-of dead/weakened pathogens
-stimulates the formations of memory cells
-vaccine can lead to symptoms as some pathogens ay be alive which can release toxins

Question 10

the use of vaccines to provide protection for individuals against disease

Answer 10

-normal immune response but memory cells are produced
-on secondary exposure to the same antigen, the secondary response therefore produces antibodies faster and at a higher concentration
-leading to destruction of pathogen e.g. agglutination/phagocytosis

Question 11

the use of vaccines to provide protection for populations against disease (herd immunity)

Answer 11

-large proportion of the population vaccinated against the disease
-makes it more difficult for the pathogen to spread through the population because more people immune so less people carry the pathogen → fewer people are susceptible to the disease

Question 12

differences between active and passive immunity

Answer 12

active
-initial exposure to antigen e.g. vaccine or primary infection
-memory cells involved
-antibody produced/secreted by b-plasma cells
-slow
-long term immunity

passive immunity
-no exposure to antigen
-no memory cells involved
-antibody introduced into body from another organism e.g. breast milk
-fast
-short term immunity

Question 13

what are the ethical issues associated with the use of vaccines?

Answer 13

tested on human → volunteers at risk of contracting the disease

tested on animals → they have a nervous system and feel pain

expensive → less money spent on research and treatment of other diseases

Question 14

explain the effect of antigen variability

Answer 14

-change in antigen shape → due to genetic mutation
-not recognised by memory b cells → no plasma cells/antibodies
-not immune
-must re-undergo primary immune response → slower / release small conc of antibodies
-symptoms felt

Question 15

explain the effect of antigen variability on vaccines

Answer 15

-change in antigen shape (due to mutation)
-exisiting anitbodies with specific shape unable to bind to changed antigens
-unable to form antigen-antibody complex
-immune system wont recognise different antigens

Question 16

monoclonal antibody

Answer 16

antibody thats produced from a sing group of genetically identical (clones) b-cells/plasma

Question 17

why are monoclonal antibodies useful in medicine?

Answer 17

-only bind to specific antigens → antibodies have a specific tertiary structure that’s complementary to a specific antigen

Question 18

monoclonal antibodies targeting medication to specific cell types by attaching a therapeutic drug to an antibody

Answer 18

e.g cancer cell
1) monoclonal antibodies made to b complementary to antigens specific to cancer cells → cancer cells are abnormal body cells w/ different antigens
2) anti-cancer drug attached to antibody
3) antibody attaches to the cancer cells →forms antigen antibody complex
4) delivers anti-cancer drug directly to specific cancer cell so drug accumulates → fewer side effects →fewer normal body cells killed

Question 19

monoclonal antibody: medical diagnosis

Answer 19

e.g. pregnancy test
-pregnant woman have hormone hCG in their urine
-urine test strip has 3 different parts with 3 different antibodies
area 1 → antibodies complementary to hCG
area 2 → antibodies complementary to the hcG antibody antigen complex\
area 3 → antibodies complementary to antibody without hcG attached

if pregnant → hcG binds o antibodies in application area (hcG antigen antibody complex)
test travel up the strip and binds at area 2

if not pregnant →no hCG in urine → doesnt bind to antibodies in application area → doesn’t bind to area 2 → no blue line
bins to antibodies at position 3 → blue line → control area