3.2.4 Cell recognition and the immune system( 3.2 Cells)

Question 1

what is an antigen

Answer 1

• foreign molecule
• that stimulates an immune response leading to production of an antibody

Question 2

how are cells identified by the immune system

Answer 2

• each type of cell has specific molecules on its surface that identify it
• often proteins - have specific tertiary structure

Question 3

what types of cells and molecules can the immune system identify

Answer 3

1) pathogens
2) cells from other organisms
3) abormal body cells
4) toxins

Question 4

Describe phagocytosis of pathogens

Answer 4

1) phagocyte attracted by chemicals / recognises antigens on pathogen
2) phagocyte engulfs pathogen by surrounding it within its cell membrane
3) pathogen contained in phagosome in cytoplasm of phagocyte
4) Lysosome fuses with phagosome and released lysozymes
5) lysozymes hydrolyse or digest pathogen

Question 5

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

Answer 5

Specific Helper T cells with complementary receptors bind to antigen on antigen - presenting cell - > activated and divide by mitosis to form clones which stimulate :
- cytotoxic t cells - kills infected cells by producing preforin
- specific b cells ( humoral response )
- phagocytes - engulf pathogens by phagocytosis

Question 6

Describe the response of B lymphocytes to a foreign antigens ( humoral response )

Answer 6

1) clonal selection :
• specific B lymphocyte with complementary receptor binds to antigen
• This is then stimulated by helper T cells
• So divided by mitosis to form clones
2) some differentiate into B plasma cells - secrete large amounts of antibody’s
3) Some different into B memory cells - remain in blood for secondary immune response

Question 7

what are antibodies

Answer 7

• quaternary structure proteins
• Secreted by B lymphocytes
• Bind specifically to antigens forming antigen - antibody complexes

Question 8

describe the structure of an antibody

Answer 8

• Antigen
• antigen binding site
• variable region
• disulfide bridge

Question 9

Explain how antibodies lead to the destruction of pathogens

Answer 9

• antibodies bind to antigens on pathogens forming an antigen - antibody complex
  -specific tertiary structure so binding site binds to complementary antigen
• Each antibody binds to 2 pathogens at a time causing agglutinations of pathogens
• Antibodies attract phagocytes
• Phagocytes bind to the antibodies and phagocytose many pathogens at once

Question 10

Explain the differences between the primary and secondary immune response

Answer 10

Primary - first exposure to antigen :
• antibodies produced slowly and lower conc
• takes time for specific plasma cells to be stimulated to produce specific antibodies
• memory cells produced
Secondary - second exposure to antigen :
• Antibodies produced faster and a at a higher concentration
• B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies

Question 11

what is a vaccine

Answer 11

• injection of antigen from weakened pathogens
• stimulating formation of memory cells

Question 12

explain how vaccines provide protection to individuals against disease

Answer 12

1) specific b lymphocytes with complementary receptors binds to antigen
2) Specific Helper T cell binds to antigen - presenting cell and stimulated B cell
3) B lymphocytes divides by mitosis to form clones
4) Dome differentiate into B plasma cells which release antibodies
5) some differentiate into B memory cells
6) On secondary exposure to antigen , B memory cells rapidly divide by mitosis to produce B plasma cells
7 ) these release antibodies faster and at a higher concentration

Question 13

explain how vaccines provide protections for population against disease

Answer 13

Herd immunity - large proportion of population vaccinated , reducing spread of pathogen
• Larger proportion of population immune so do not become ill from infection
• Fewer infected people to pass pathogen on / unvaccinated people less likely to come in contact with someone with disease

Question 14

Describe the difference between active and passive immunity

Answer 14

Active :
- initial exposure to antigen
- memory cells involved
- Antibody produced and secreted by B plasma cells
- Slow - longer to develop
- Long term immunity as antibody can be produced in response to a specific antigen again

Passive immunity
- No exposure to antigen
- No memory cells involved
- Antibody introduced from another organisms
- Faster acting
- Short term immunity as antibody hydrolysed

Question 15

Explain the effect of antigen variability on disease and disease prevention

Answer 15

• antigen on pathogens changes shape / tertiary structure due to gene mutations
• so no longer immune
- b memory cell receptors cannot bind to do antigen on secondary exposure
- Specific antibodies not complementary to changed antigen

Question 16

Describe the structure of a HIV particle

Answer 16

• Lipid envelope
• RNA
• reverse transcriptase
• Capsid
• attachment protein

Question 17

Describe the replication of HIV in helper T cells

Answer 17

1) HIV attachment proteins attach to receptors on T helper cells
2) lipid envelope fixed with cell surface
membrane , releasing capsid into cell
3) capsid uncoats , releasing RNA and reverse transcriptase
4) reverse transcriptase converted viral RNA to DNA
5) Viral DNA inserted into helper T cell DNA
6) Viral protein / capsid / enzymes
produces
- DNA transcribed into HIV mRNA
- HIV mRNA translated into new HIV proteins
7) Virus particles assembled and released from cell

Question 18

Explain how HIV caused the symptoms of AIDS

Answer 18

• HIV infects and kills helper t cells as it multiples rapidly
  • so helper t cells can’t stimulate cytotoxic t cells , B cells and phagocytes
  • So B plasma cells can’t release as many antibodies for agglutination and destruction of pathogens
• immune system deteriorates - more susceptible to infections
• Pathogens reproduced , release toxins and damage cells

Question 19

Explain why antibiotic are ineffective against viruses

Answer 19

• viruses don’t have metabolic processes / ribosomes
• Viruses do not have bacterial enzymes / murein cell wall

Question 20

what is a monoclonal antibody

Answer 20

• antibody produced from genetically identical / cloned B lymphocytes / plasma cells
• So have same tertiary structure

Question 21

Explain how monoclonal antibodies can be used in medical treatments

Answer 21

• monoclonal antibody has a specific tertiary structure
• Complementary to specific receptors found on a specific cell type
• therapeutic drug attached to antibody
• Antibody binds to specific cell , forming antigen - antibody complex

Question 22

explain how monoclonal antibodies can be used in medical diagnosis

Answer 22

• monoclonal antibody has a specific tertiary structure
• complementary to specific receptor
• Dye / stain attached to antibody
• Antibody binds to receptor forming antigen - antibody complex

Question 23

Explain the use of antibodies in the ELISA test to detect antigens

Answer 23

Example method 1 :
1) attach sample with potential antigens to well
2) add complementary monoclonal antibodies with enzymes attached - bind to antigens if present
3) wash well - remove unbound antibodies
4) add substrate - enzymes create produced that cause a colour change
Example method 2 :
1) attach specific monoclonal antibodies to well
2) add sample with potential antigens , then wash well
3) add complementary monoclonal antibodies with enzymes attached - bind to antigens if present
4) wash well - remove unbound antibodies
5) add substrate - enzymes create produced that cause a colour change

Question 24

Suggest the purpose of a control well in the ELISA test

Answer 24

• compare test to show only enzyme causes colour change
• compare to test to show all unbound antibodies have been washed away

Question 25

Suggest why failure to thoroughly wash the cell can result in a false positive in the ELISA test

Answer 25

• antibody with enzyme remains
• so substrate converted into colour product

Question 26

Discuss some general ethical issues associated with the use of vaccines and monoclonal antibodies

Answer 26

• preclinical testing on animals - potential stress / harm
  • but animals not killed and helps to produce new drugs to reduce human suffering
• Clinical trials on humans - potential harm / side effects
• Vaccines - may continue high risk activities and still developed
• Use of drugs -
  potentially dangerous side effects