Cells Part 3- Immune Responnse, Antibodies, HIV

Question 1

What is an antigen

Answer 1

A foreign protein that stimulates an immune response

Question 2

Where can antigens be found

Answer 2

The cell surface of an microorganisms
Surface of a virus
Cell surface of tissues/ organ transplant
Free molecules- e.g. toxin

(Cells form other organisms, cancer cells, cells infected by a virus, pathogen)

Question 3

What are the non-specific defence mechanisms (first line)

Answer 3

Response is immediate and same for all pathogen
First line
- skin- hard for microbes to digest, fatty acids inhibit growth of microorganisms
- mucous membrane - trap microbes
-ciliated epithelium - trachea, bronchioles - sweep mucus
- tears, saliva

Question 4

What is the second line of defence

Answer 4

Phagocytic white blood cells

Question 5

What is the third line of defence

Answer 5

Cells mediated response
T lymphocytes

Humorla response
B. Lymphocytes

Question 6

Describe phagocytosis

Answer 6

A phagocyte recognises the foreign antigen
When the pathogen is englufued into the cell a vesicle forms called phagosome
Phagosomes fuse with another vesicle that’s contains hydrolytic enzymes (lysomes)- forming phagolysosomes
Hydrolytic enzymes hydrolyse th pathogen
Waste material is digested
The pathogens antigen are then present on the surface of the phagocyte to aid activation of specific immunity - antigen presenting cell

Question 7

What do helper T-cells do

Answer 7

Stimulate b-cells to divide
Secrete interferon and cytokines to stimulate cytotoxic T cells, activate b-cells, phagocytosis

Question 8

What do cytotoxic t-cells do

Answer 8

Kills body’s abnormal cells
Protein inserts itself into membrane and makes a hole

Question 9

What do B-lymphocytes do

Answer 9

Specie b cell will have a complementary antibody on its surface
Teach to one another and antigens enter b cells by endocytosis and no wpresente don its surface (APC)

Helper T cell binds to antigen stimulating b cells to divide

Divide by mitosis
Plasma- antibodies
Me both- quicker and higher conc.

Question 10

What is an antibody

Answer 10

Protein specific to an antigen

Question 11

Describe the role of antibodies in stimulating phagocytosis

Answer 11

Bind to antigen/ ar markers
Antibodies causes clumping/ agglutination
Attract phagocytes

Question 12

What is the structure of antibodies

Answer 12

Quaternary structure- 4 polypeptide chains
2 heavy, 2 light
Help by disulphide bonds
Variable region- antigen binding site

Question 13

What do antibody do

Answer 13

1. Agglutination
2. Stimulate phagocytosis
3. Precipitation
4. Prevent attachment of cells

Question 14

What are monoclonal antibodies

Answer 14

Identical copes of one type of natibody
Made form same type of plasma b-cell

Question 15

What are the uses of monoclonal antibodies

Answer 15

Immunoassay
Cancer treatment
Reducing rejection
Research
Identify plant disease

Question 16

Describe the ELISA test

Answer 16

Indirect ELISA test for an antigen-
1. Apply the sample to a surface to which the antigen in the sample will attach
2. Wash the surface several times to remove any unattached antigens
3. Add the antibody that is specific to the antigen you are searching for, and leave it to bind
4. Wash the surface again to remove excess antibody
5. Add a second antibody that bind sot the first antibody, it also has an enzyme attached to it
6. Ad the colourless substrate of the enzyme. The enzyme acts on the substrate to change it to a coloured product
7. Th amount of antigen present present is relative to the intensity of colour that develops
Direct ELISA test
+ $ 1. Add monoclonal antibody to the well which are fixed on the bottom of the well. Ad the sample
and the antigen binds to the antibody
2. Add the second monoclonal antibody, linked to the enzyme, which binds to the antigen
a. Wash and rinse to remove any antibody which is unbound, e.g. as there’s no antigen
3. Add the coloured substrate which is converted by the enzyme into the coloured product

Question 17

Describe how pregnancy test work

Answer 17

…

Question 18

How do monoclonal antibodies destroy cancer cells

Answer 18

Specie
Attach to receptors
Block signals that stimulate uncontrollable growth

• indirect
  Radioactive drug

Question 19

An antigen in a vaccine leads to the production of antibodies. Describe the part played by b-lymphocytes

Answer 19

1. Antigen binds to/is complementary to receptors on B
   lymphocyte; binds to a specific B lymphocyte
2. Selected B lymphocyte becomes an APC
3. B lymphocyte becomes competent/activated; (as a result of TH cells)
4. B lymphocytes reproduce by mitosis /B lymphocytes cloned
5. Plasma cells secrete antibodies

Question 20

What is immunity

Answer 20

Acquired characteristic of your immune system that cannot be inherited

Question 21

What is active immunity

Answer 21

Body make sown antibodies after being stimulated by an antigen
Natural- getting ill, artificial - vaccine

Question 22

What is passive immunity

Answer 22

Ready-made antibodies
Natural- breastfeeding
Artificial - antibody injections

Question 23

What are the advantages and disadvantages of active/ passive immunity

Answer 23

Active involves memory cells, passive does not;
Active involves production of antibody by plasma cells / memory cells;
Passive involves antibody introduced into body from outside / named source:
Active long term, because antibody produced in response to antigen:
Passive short term, because antibody (given) is broken down;
Active (can) take time to develop / work, passive fast acting.

Question 24

Describe how HIV works

Answer 24

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/capsid/enzymes produced;
5. Virus (particles) assembled and released (from cell);

RNA converted into DNA using reverse transcriptase;
Reject ‘messenger’ or ‘m’ before RNA
DNA incorporated/inserted into (helper T cell)
DNA/chromosome/genome/nucleust
DNA transcribed into (HIV m)RNA;
Accept descriptions of transchption
(HIV mRNA) translated into (new) HiV/viral proteins (for assembly into viral particles):
Accept descriptions of translation
Accept named viral protein, eg capsid
Reject viral cells

Question 25

How does HIV causes symptoms of AIDS

Answer 25

HIV destroys helper cells
B-cells aren’t activated
No long term immunity

Opportunistic infection- infections which would not normally pose a threat

Question 26

Why don’t antibodies work on HIV

Answer 26

No cell wall in viruses- only protein coat
Hide within cells - cannot reach them