Unit 2 Immunology

Question 1

Describe the process of phagocytosis

Answer 1

The phagocyte engulfs the bacteria enclosing it in a phagocytic vesicle;
The lysosomes fuse with the vesicle;
hydrolysing the molecules of the bacteria destroying it;

Question 2

Describe the structure of an antibody

Answer 2

1. 4 polypeptide chains ;
2. 2 heavy, 2 light;
3. held together by disulfide bonds;
4. there is a constant region that is the same in all antibodies;
5. and a variable region which contains the antigen binding sites;
6. This is different in different antibodies;
7. The antigen binding site has a specific tertiary structure complementary to a specific antigen;

Question 3

Describe the humoral response

Answer 3

1. Theantibody on the surface of the B cellbinds to the antigen on the pathogen;
2. Forming an antibody-antigen complex;
3. T helper cells also stimulate the B cell;
4. causing the B cell to divide by mitosis;
5. These B cells are clones so all have the same complementary shaped antibody to the antigen;
6. They differentiate into plasma B cells and memory B cells;
7. Plasma B cells secrete the antibody into the blood for agglutination;

Question 4

What is antigenic variation?

Answer 4

Mutations in the genetic material of the pathogen;
Leads to a change in the amino acid sequence of it’s antigen;
changing the antigens tertiary structure;

Question 5

Describe the role of T cells in specific immunity

Answer 5

1. T cells bind to specific antigens via t cell receptors on cell surface membrane;
2. T cell divides by mitosis;
3. Memory T cells provide long term immunity;
4. Helper T cells stimulate B cells to divide by mitosis;
5. Cytotoxic T cells release chemicals to destroy cells directly;

Question 6

Describe how HIV replicates

Answer 6

1. The glycoprotein spikes attach to the CD4 receptor on the T helper Cell;
2. Lipid envelope fuses with the host cell membrane;
3. Capsid enters and breaks open;
   4.Viral RNA is used to make viral DNA via reverse transcriptase;
4. Viral DNA enters the nucleus;
5. Viral DNA is used in protein synthesis to make viral RNA and viral proteins;
6. They assemble to make more viruses;
7. These bud out of the cell to infect more cells;

Question 7

Explain how HIV affects the production of antibodies when AIDS develops in a patient.

Answer 7

1. T helper cell numbers decrease;
2. T helper cells can’t stimulate B cells;
3. To divide by mitosis and differentiate into plasma cells;
4. So antibody production decreases;

Question 8

Describe the direct ELISA test.

Answer 8

1. Monoclonal antibody is bound to the plastic surface;
2. The sample to be testedis added to the well;
3. If the antigen is present, it will bind to the monoclonal antibodies to form antibody-antigen complexes;
4. A second monoclonal antibody(also specific for the same antigen), which has an enzyme attached, is added
5. The well is then washed to remove any unbound second antibody
6. Substrate (usually colourless), for the enzyme is added and we will only get a colour change if the specific antigen was present in the sample;
7. A negative result would stay colourless;

Question 9

Describe the indirect ELISA test

Answer 9

1. Antigen is bound to the plastic surface;
2. The sample to be testedis added to the well;
3. If the antibody is present in the sample, it will bind to the antigen on the welltoform antibody-antigen complexes;
4. A second monoclonal antibody (specific for the antibody),which has an enzyme attached, is added;
5. The well is then washed to remove any unbound second antibody
6. Substrate for the enzyme is added and we willonly get acolourchange if the specific antibody was present in thesample;