Cell Structure - Cell Recognition And The Immune System

Question 1

Describe what is meant by an antigen

Answer 1

An antigen is A foreign molecule that stimulates an immune response
They are often proteins or glycoproteins

Question 2

State which cells and molecules enable the immune system to identity

Answer 2

Pathogens
Abnormal body cells
Toxins
Cells from other individuals in the same species

Question 3

Describe the process of phagocytosis

Answer 3

1. Phagocyte recognises antigen as foreign
2. The pathogen is engulfed by the phagocyte
3. Engined pathogen is contained inside a vesicle called a phagosome
4. Lysosomes fuse with the phagosome and releases lysozymes into the phagosome
5. Lysozymes hydrolyse the molecules

Question 4

Describe the process of the cellular response

Answer 4

1. Phagocyte engulfs the pathogen,hydrolyses it and presents the antigen on the surface of its membrane
2. Helper t-cell with specific hcomplementary receptor, binds to and is activated
3. The activated t-helper cell then releases chemical signals which further activate:
   More phagocytes
   Cytoxic t-cells which kill infected cells directly
   Specific B-cells

Question 5

Describe the process of the humoral response

Answer 5

1. Specific B cells are activated by their specific T helper cell.
2. B cells clone into memory cells and plasma cells
3. Plasma cells secrete specific antibodies which bind to the foreign pathogen

Question 6

Define the term monoclonal antibody

Answer 6

Antibodies with the same tertiary structure which are complementary to and bind to one type of antigen and come from the same type of B cell

Question 7

Explain how antibodies lead to the destruction of pathogens

Answer 7

1. When an antibody binds to an antigen it is known as an antigen-antibody complex
2. This causes pathogens to lump together (agglutination)
3. Many cells can now be engulfed by a phagocyte in one go

Question 8

Describe the primary immune response

Answer 8

When the antigen infects the body for the first time

Antibodies are produced more slowly

There are less antibodies as it take time for clonal selection

Symptoms occur

Question 9

Describe the secondary immune response

Answer 9

Produced due to the presence of specific memory B cells

Clonal selection occurs more quickly

Plasma cells produce many more antibodies at a faster rate

The infection is overcome before symptoms can occur

Question 10

What is a vaccine?

Answer 10

Vaccines contain antigens from the pathogen

Vaccinations make an individual immune to a certain antigen

They create a primary response against an antigen so that memory B cells are formed with complementary antibodies without the symptoms of the pathogen itself

Question 11

Describe the process by which a vaccine makes a person immune to a pathogen

Answer 11

1. Vaccines contain antigens from the pathogen
2. A phagocyte engulfs the antigen and presents it on its surface membrane
3. A specific helper T cell with a complementary receptor protein binds to the antigen
4. This helper T cell stimulates a specific B cell which divides by mitosis
5. B cells clone into plasma cells which produce + secrete many antibodies
6. The antibodies agglutinate the antigen and destroy it
7. Memory B cells are produced so on a second exposure to the antigen, more antibodies are produced more quickly, destroying the pathogen before symptoms are displayed

Question 12

Describe what herd immunity is and explain how it protects unvaccinated individuals in a population

Answer 12

If a majority of the population are vaccinated then most people cannot get the disease

Therefore those who are not vaccinated are also protected as there are less people to transmit the disease

Question 13

Give 3 ethical issues regarding the use and production of vaccines

Answer 13

1. The vaccine may have side effects and the risk and severity of the side effects can vary between vaccines
2. Development and testing may involve use of animals
3. People may be forced to have vaccines even if they do not agree with them

Question 14

Describe what antigenic variability is and how it arises

Answer 14

Due to mutations in pathogen DNA, tertiary structure of antigen protein can change shape

In a second exposure, the antigen binding site of antibodies from the memory cells will not be complementary and a second response does not occur

Question 15

Explain how antigenic variability reduces the effectiveness of vaccines

Answer 15

Vaccines become ineffective as antibodies produced as a result of the vaccine are no longer complementary

A new vaccine needs to be made each time the antigen changes which take time and is expensive

Question 16

Contrast the differences between active and passive immunity

Answer 16

Active immunity:
- following exposure to an antigen, specific memory B cells are made which produce antibodies against antigen
Passive immunity:
- antibodies against the antigen are put straight into the body, the immune system does not make the antibodies

Question 17

State the advantages of active immunity

Answer 17

Immunity is longer lasting

Question 18

State the disadvantages of active immunity

Answer 18

• Take more time to make memory cells and become immune
• In natural active immunity you will get symptoms of the disease
• In artificial active immunity you can only administer the vaccine before getting the disease

Question 19

State the advantages of passive immunity

Answer 19

• Can be given after exposure to antigen / pathogen
• Works straight away

Question 20

State the disadvantages of passive immunity

Answer 20

• Short term as antibodies become broken down
• Short term as no memory cells are produced

Question 21

Describe one use of monoclonal antibodies in treating disease

Answer 21

Treating cancer:
- monoclonal antibodies which have anti-cancer drug can be made complementary to the cancer cell antigen
- monoclonal antibodies bind only to cancer cells + kill them
- fewer healthy cells are damaged

Question 22

Describe one use of monoclonal antibodies in diagnosing disease

Answer 22

Pregnancy tests:
- test strip contains hCG monoclonal antibody with a coloured dye attached
- urine flows along test strip and any hCG binds to monoclonal antibody
-hCG- antibody complexes with dye bind to fixed hCG antibody and build up on test line causing a coloured band to appear
- if no hCG present then antibodies flow to control line
- colour of test line changes confirming test worked correctly and is a negative result

Question 23

Describe the stages involved in the ELISA test

Answer 23

1. The antigen is bound to the bottom of a plastic well
2. Sample is added + if antigen is present then it binds to antigen
3. The well is washed to remove any unbound antibody
   4.2nd antibody complementary to 1st is added and it has an enzyme attached to it
4. The well is washed again to remove unbound 2nd antibody
5. Solution containing substrate is added
6. Enzyme on 2nd antibody reacts to substrate, producing a colour change which is a positive result for the presence of antibody

Question 24

Explain how HIV infects and replicates in helper t-cells

Answer 24

1. The attachment protein on HIV binds to a complementary receptor on the helper T-cell
2. The capsid enters the cell and releases the RNA into the cytoplasm
3. Reverse transcriptase makes DNA from the HIV RNA
4. Using the host cell’s enzymes and ribosomes for protein synthesis, viral proteins are made from the DNA
5. New virus particles are formed from the proteins which bud from the cell and infect more helper T-cells

Question 25

Explain how HIV causes AIDS

Answer 25

1. HIV kills helper T-cells
2. When helper T- cell numbers become low, the immune system starts to fail and serious infections can kill the patient

Question 26

Why do antibiotics not kill viruses?

Answer 26

Antibiotics target parts of bacteria which are not found in a virus

Viruses are hard to kill because they replicate inside cells and have few drug targets