Unit 2 - Cell Immunity

Question 1

Describe what the immune system is able to identify through the specific molecules located on the cell surface.

Answer 1

• Pathogens
• Abnormal body cells
• Toxins
• Cells from other organisms of the same species

Question 2

Define what is meant by an antigen.

Answer 2

• Cell surface molecule which stimulates an immune response
• Enables identification of
  Pathogens
  Abnormal body cells
  Toxins
  Cells from other organisms of the same species

Question 3

Describe the effect of antigen variability on disease

and disease prevention.

Answer 3

• Pathogen’s DNA mutates frequently resulting in the new shape of antigens made due to different primary structure
• Therefore memory cells are no longer complementary to anitigen

Question 4

Describe the process of phagocytosis

Answer 4

• Phagocyte moves towards pathogen via chemotaxis and surrounds pathogen as recognises foreign antigen
• Phagocyte cytoplasm engulfs the pathogen into vacuole to form a phagosome
• Phagosome and Lysosome fuse and release digestive enzymes lysozymes
• Which hydrolyse/digest the pathogen/bacteria
• Antigens displayed on the cell membrane

Question 5

Describe what is meant by an antigen-presenting cell

Answer 5

• A macrophage that displays antigen from the pathogen on its surface/cell membrane
• This allows for recognition from T-cells

Question 6

Describe the cell-mediated response.

Answer 6

1. Once the pathogen is destroyed, antigens presented on its cell membrane(APC)
2. Complementary T-lymphocyte binds to foreign antigen on APC
3. Activating T-lymphocyte, therefore, produces clones of complementary T helper cell by mitosis
4. Cloned complementary T-helper cells then stimulate:
   =cytotoxic T- cells
   =B-cells (humoral response)
   =Phagocytes for phagocytosis
   OR become memory cells

Question 7

Describe the humoral response.

Answer 7

1. Antigen binds to the complementary antibody on membrane of the B-cell to form antigen-antibody complex
2. Antigen enters the B-cell by endocytosis so B-cell becomes an APC
3. Activated complementary T-cell binds to the B-cell causing B-cell to undergo clonal expansion
4. B-cells reproduce by mitosis & differentiate into plasma cells OR MEMORY cells
   - Plasma cells secrete antibodies with the complementary variable region to antigen

Question 8

Define an antibody

Answer 8

• A protein secreted by plasma cells

- Quarternary structure protein

Question 9

Describe the structure of an antibody

Answer 9

(2 heavy chains)
(2 light chains held by disulfide bridges to connect polypeptide chains)
- Binding sites on the variable region have specific tertiary structure complementary to an antigen
- Rest of the molecule known as the constant region

Question 10

How do antibodies lead to the destruction of a pathogen?

Answer 10

• Antigen-antibody complex is formed
• Which leads to the destruction of pathogens through agglutination
• Which enhances phagocytosis

Question 11

Describe the role of a memory cell.

Answer 11

• Specialised T-helper cell/Memory B -cell
• Remain in low levels in the blood
• Which can divide rapidly by mitosis & differentiate if encounters the same pathogen before symptoms occur

Question 12

Describe the difference between the primary and secondary immune response.

Answer 12

In secondary response:

• Faster rate of antibody production compared to primary so antibody levels remain higher
• Pathogen usually destroyed before any symptoms

Question 13

Describe the difference between passive and active immunity.

Answer 13

(faster)
PASSIVE - No exposure to antigen, Involves antibodies
Natural - Antibodies in breast milk
Artificial - Needle stick injections

ACTIVE - Requires exposure to antigen, Involves antibodies
Natural - Immune response after disease
Artifical - Vaccination

Question 14

Describe the process of vaccination.

Answer 14

• Inactive/Dead form of pathogen/antigen injected into body
• Triggers primary immune response where B cells undergo clonal expansion
• Memory cells are produced which can differentiate into plasma cells which make complementary antibodies to anitgen
• Memory cells remain in bloodstream and differentite ino plasma cells which rapidly produce antibodies so secondary response is rapid
• Higher concentration of antibodies in blood therefore antigens destroys pathogen before the symptoms

Question 15

Describe the concept of herd immunity.

Answer 15

• Vaccinating large proportions of the population reduces available carriers of pathogens
• Which protects those who are not vaccinated
  e. g People with a weak immune system

Question 16

Describe the structure of HIV.

Answer 16

• Genetic material RNA and enzyme reverse transcriptase surrounded by protein capsid at the core
• Phospholipid viral envelope
• GP120 attachment proteins on the surface

Question 17

Describe how HIV replicates in a T Helper cell

Answer 17

• Attachment proteins on virus bind to the complementary CD4 receptor on T Helper cells
• HIV protein capsule fuses with TH cell enabling RNA & enzymes to enter
• HIV enzyme reverse transcriptase copies viral RNA into DNA copy and moves it to the TH cell nucleus
• mRNA transcribed and TH cell creates viral proteins and viral proteins released from cell

Question 18

Describe how HIV leads to aids.

Answer 18

• Attachment proteins on virus bind to the complementary CD4 receptor on T Helper cells
• HIV particles replicate in TH cells causing them to be destroyed
• AIDS develops when there are too few T Helper cells for the immune system to function
• Individuals cannot destroy other pathogens or secondary infections

Question 19

Describe why antibiotics are ineffective against viruses.

Answer 19

• Antibiotics work by damaging murein cell walls but viruses have no cell walls
• Viruses replicated inside host cells so difficult to destroy without damaging normal body cells

Question 20

Define a monoclonal antibody

Answer 20

Antibodies produced from a single clone of B cells

Question 21

Describe the importance of monoclonal antibodies in targeting medication to specific cell types.

Answer 21

• Targeted treatment by antibodies being attached to therapeutic drugs & carrying drugs to specific cells

Question 22

Describe the importance of monoclonal antibodies in medical diagnosis.

Answer 22

Pregnancy tests

• Detecting HCG hormone in the urine of women
• Any HCG hormone binds to antibodies on beads to form an antigen-antibody complex
• Which causes test trip to turn blue if pregnant as antibodies with HCG are immobilised

Question 23

Describe the importance of monoclonal antibodies in the ELISA test.

Answer 23

• Antigens bind to the bottom of the test plate
• First antibody complementary in shape to the antigen binds to antigen to form antigen-antibody complexes
• Second antibody with enzyme attached added to bind to the first antibody
• Solution/substrate added and colour changes if positive

Question 24

Describe ethical issues of the use of vaccines and monoclonal antibodies.

Answer 24

VACCINES
Animal rights issues - some people disagree animals should be used in this way as may cause harm
Potentially dangerous side effects with humans being tested

MONOCLONAL ANTIBODIES
Animal rights issues - some people disagree animals should be used in this way