Immunology A1

Question 1

Describe the non-specific defence mechanisms the body may launch against pathogens
(5 marks)

Answer 1

The process is called phagocytosis – No Mark
1. Pathogen is engulfed by the phagocyte.
2. Engulfed pathogen enters the cytoplasm of
the phagocyte in a vesicle;
3. Lysosomes fuse with vesicle releasing
digestive enzymes;
4. Lysosome enzymes break down the
pathogen.
5. Waste materials are ejected from the cell by
exocytosis;

Question 2

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism.
Describe how.

Answer 2

1. Vaccine contains antigen from pathogen;
2. Macrophage presents antigen on its surface;
3. T (helper) cell with complementary receptor
   protein binds to antigen;
4. T cell stimulates B cell;
5. (With) complementary antibody on its
   surface;
6. B cell divides to form clone secreting /
   producing same antibody;
7. B cell secretes large amounts of antibody;

Question 3

Describe the difference between active and
passive immunity. (6)

Answer 3

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 4

State why some antibodies are referred to as
monoclonal.

Answer 4

(Antibodies) produced from a single clone of B cells / plasma cells;
OR
(Antibodies) produced from the same B cell / plasma cell;

Question 5

What is specific immunity and why is it effective?

Answer 5

A specific response to an antigen on the surface of a cell or pathogen that has been recognised as non-self.

Question 6

Define antigen.

Answer 6

1. an antigen is a molecule (usually protein)
2. that stimulates an immune response resulting in the production of specific antibodies
3. the body recognises the pathogen/antigen as ‘non-self’.

Question 7

Why are viruses usually out of reach to antibiotics?

Answer 7

1. they use host cells to carry out metabolic activities in so don’t have any reaction to disrupt.
2. they have a protein coat rather than a murein cell wall which doesn’t allow antibiotics to work as they do with bacteria.

Question 8

How does HIV replicate? (5)

Answer 8

1. HIV attaches to receptor on lymphocyte
2. HIV injects its genetic material into the lymphocyte, which becomes a host cell
3. HIV uses the lymphocytes cellular machinery to make copies itself
4. after making many copies of itself, the host cell is destroyed by HIV
5. HIV infection eventually leads to decreased lymphocyte numbers and reduced ability to produce antibodies

Question 9

What is a vaccine?

Answer 9

1. certain protein/weakened microorganism
2. stimulates production of antibodies + produce memory cells

Question 10

How do antibiotics work?

Answer 10

1. by preventing bacteria making normal cell wall (murein)
2. so bacteria is unable to resist osmotic pressure and the cells burst

Question 11

Define antibody.

Answer 11

1. protein/glycoprotein made in response to foreign antigen
2. has binding sites which specifically bind to antigen (only active sites in enzymes, everything else = binding site)
3. produced by B cells

Question 12

What is an antigen-antibody complex?

Answer 12

1. specific antibody binds with specific antigen
2. causing an antigen-antibody complex

Question 13

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism.
Describe how.
-cellular response (mark 1-3)
-humoral response (4-7)

Answer 13

1. vaccine contains antigen from pathogen
2. macrophage (antigen presenting cell) presents antigen on its surface
3. T (helper) cell with complementary receptor protein binds to antigen
4. T cell stimulates B cell
5. (with) complementary antibody on its surface
6. B cell divides to form clone secreting/producing same antibody (via mitosis)
7. B cell secretes large amounts of antibody

Question 14

What is clonal selection?

Answer 14

1. a specific T cell binds to presented antigen via its complementary receptor
2. T cell is activated and clones produce many T cells with complementary receptors to the antigen.

Question 15

When a T cell is activated, it clones into two different types of T cell.
Name and describe the role of each T cell.

Answer 15

1. cytotoxic T cell (killer t) - locate and destroy body cells (to stop infections spreading) that are already infected by the pathogens that caused the immune response.
2. Helper T cell - releases chemicals (cytokines) that attract phagocytes and B cells to the area of infection. Activates B cells (you start feeling better).

Question 16

How do antibodies help destroy pathogens?

Answer 16

1. the antibodies bind to the antigens on pathogen and clump them together, allowing phagocytes to recognise and destroy the pathogen more efficiently (agglutination - to thicken).
2. in the case of bacteria, the antibodies bind to the surface of the bacteria and damage the bacterial cell membrane. This causes the bacterial cell lyses leading to its destruction (dies because it cannot respire).

Question 17

Explain the role of memory cells.

Answer 17

1. they remain in circulation in case of future re-infection by the same pathogen
2. they RECOGNISE not remember
3. if the memory cell encounters the antigen on another occasion, they are activated and divide rapidly
4. the memory cells clone into plasma cells and more memory cells
5. the plasma cells produce the specific antibodies for the invading pathogen, but without the need for time consuming primary response

Question 18

What is antigenic variability

Answer 18

1. some pathogens have antigens which mutate and change shape eg. flu and HIV
2. when this occurs, pathogen is not recognised by memory cells from previous infection (no longer complementary)
3. so the individual will not be able to initiate a secondary response

Question 19

Describe the difference between active and passive immunity.

Answer 19

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 (eg given by mother or antiserum)
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 (have to go through an immune response)

Question 20

What does a non-harmful version of a pathogen have to be for a vaccine?

Answer 20

1. dead
2. weakened
3. attenuated (genetically altered to not make you ill)

Question 21

What is herd immunity?

Answer 21

If enough individuals in a population are vaccinated, the there is little chance of the disease spreading, therefore even non-vaccinated individuals will be protected.

Question 22

Name some ethical issues associated with vaccines and their development.

Answer 22

1. testing on animals (infringement of rights)
2. human testing (put at risk - usually volunteers though)
3. availability to everyone (or only people that can afford it) - 3rd world countries.
4. balancing risk of side effects against possible benefits
5. should it be compulsory if society benefits?
6. should we be aiming to eliminate an organism (loss of genetic diversity)

Question 23

State why some antibodies are referred to as monoclonal.

Answer 23

(antibodies) produced from a single clone of B cells/plasma cells
OR
(antibodies) produced from the same B cell/plasma cell

Question 24

Tests using monoclonal antibodies are specific.
Use your knowledge of protein structure to explain why.

Answer 24

1. (specific) primary structure/order of amino acids
2. (specific) tertiary / 3D structure/shape
3. so only binds to/fits complementary to one antigen

Question 25

Describe a method used to produce monoclonal antibodies.

Answer 25

1. inject mouse (has to be living) with a pathogen to stimulate production of immune cells and antibodies
2. B cells are isolated and fused with tumour cells from a mouse
3. the resulting hybridoma cells can survive and keep dividing, producing quantities or antibodies (as tumour cells divide)
4. the antibody that is specifically required is isolated and then cloned to produce unlimited quantities of monoclonal antibodies.

Question 26

Give 6 uses of monoclonal antibodies.

Answer 26

1. research
2. Immunoassays (pregnancy test kits etc)
3. diagnosis (showing presence of particular antigen)
4. targeting drugs
5. killing specific cells
6. isolating specific chemicals

Question 27

What is HIV and what does it cause?

Answer 27

1. human immunodeficiency virus
2. causes the disease AIDS (acquired immune deficiency syndrome)

Question 28

Describe the ELISA test step by step.

Answer 28

1. monoclonal antibodies bond to surface of vessel
2. sample containing chemical to be detected or positive control binds to antibody due to complementary shape
3. second monoclonal antibodies with enzyme (colour) attached added and also binds to chemical
4. then washed - so any unbound enzymes wash away (avoid false positives)
5. substrate added - chemical colour change visible
6. confirms presence of chemical

Question 29

Describe how HIV is replicated?

Answer 29

1. Attachment proteins attach to receptors on helper T cell/lymphocyte
2. Nucleic acid/ RNA enters cell
3. Reverse transcriptase converts RNA to DNA
4. Viral protein produced
5. Virus particles assembled + released from cell