The Immune System

Question 1

what 4 things do specific molecules on the CSM allow for identification of?

Answer 1

Pathogens
Cells from other organism of the same species (eg from organ donation)
Toxins (produced by pathogens)
Abnormal body cells (cancer)

Question 2

antigen

Answer 2

protein on cell surface which may be recognised by the immune system and induce an immune response.

Question 3

process of phagocytosis

Answer 3

1. Phagocyte is attracted to the pathogen by chemicals (toxins) the pathogen releases and its foreign antigen.
2. The phagocyte ingests the pathogen, which is enclosed in the phagosome.
3. Lysosomes, which contain lysozymes (enzymes) fuse with the phagosome and release the enzymes into it.
4. The enzymes hydrolyse the pathogen’s molecules
5. The phagocyte absorbs the products of hydrolysis

Question 4

how are ingested pathogens destroyed after phagocytosis?

Answer 4

lysozymes, hydrolytic enzymes, are released into the phagosome containing the pathogen. Lysozymes hydrolyse and destroy the pathogen.

Question 5

what do helper T cells respond to?

Answer 5

specific foreign antigens presented on the CSM of body cells which have engulfed the pathogen

Question 6

what is a pathogen?

Answer 6

microorganism that causes disease/ an immune response

Question 7

which type of immune response involves helper T cells?

Answer 7

cellular response

Question 8

what are body cells that present foreign antigens from pathogens on their CSM called?

Answer 8

antigen-presenting cells.

Question 9

Process of the cellular immune response

Answer 9

1- Pathogens invade body cells or are engulfed by phagocytes (phagocytosis)
2- The body cell places the pathogen antigens on its cell surface membrane
3- Specific TH (helper T) cells have receptors that can fit exactly onto the antigens.
4- This attachment activates the TH cell to divide by mitosis to form a clone of genetically identical cells.
5- The cloned T cells:
- Develop into memory cells ⇒ rapid response on reinfection
- Stimulate phagocytosis of pathogens
- Stimulate division of B cells ⇒ secrete antibodies
- Activate cytotoxic T cells (TC cells)

Question 10

which type of immune response are B cells involved in?

Answer 10

the humoral response - response to foreign antigens present in body fluids.

Question 11

what 4 things do cloned helper T cells stimulate?

Answer 11

• Develop into memory cells ⇒ rapid response on reinfection
• Stimulate phagocytosis of pathogens
• Stimulate division of B cells ⇒ secrete antibodies
• Activate cytotoxic T cells (TC cells)

Question 12

Humoral immune response (B cells) stages:

Answer 12

antibodies on the surface of a specific B cell bind to a complementary foreign antigen.
helper T cells activate the B cell to divide by mitosis and form a clone. This is clonal selection.
Plasma cells are formed.

Question 13

Role of plasma cells in the humoral immune response

Answer 13

plasma cells produce and secrete the antibody specific to the foreign antigen. This is part of the primary immune response.

Question 14

Role of memory cells from the secondary immune response

Answer 14

remain in the blood and can respond to future infections by the same pathogen. Upon reinfection they divide rapidly to form plasma cells which secrete the antibodies. This is the secondary immune response.

Question 15

primary immune response

why slow?

Answer 15

primary:
occurs when an antigen enters the body for the first time. this is slow because there aren’t many of the correct B cells initially, it takes time for clonal selection and antibody production to occur.
symptoms of disease are shown. memory cells are produced.

Question 16

antibody

Answer 16

These are proteins with specific binding sites complementary to a specific antigen which are synthesised by B cells.

Question 17

antibody structure

Answer 17

• Formed of 4 polypeptide chains in 2 pairs. Y shape
• One pair of heavy chains
• One pair of light chains
• Each antibody has 2 specific binding sites complementary to a specific antigen. These binding sites are formed of specific amino acids and have a specific 3D shape.
• Binding of antigen and antibody forms an antigen-antibody complex.
• The constant region is the same in all antibodies and the variable region contains the binding sites and differs.

Question 18

secondary immune response

Answer 18

if the same pathogen enters the body for a second time, a quicker, stronger secondary immune response is stimulated. Clonal selection occurs more quickly because memory cells exist and are activated to divide into plasma cells which can produce the correct specific antibody.
The pathogen is destroyed before symptoms of the disease show.

Question 19

Function of antibodies

Answer 19

Antibodies cause agglutination of the bacterial cells as each antibody has 2 binding sites. Agglutination forms clumps of bacterial cells, making it easier for these cells to be located and destroyed by phagocytes as they are less spread out.

Question 20

what is formed when an antibody binds with its complementary antigen?

Answer 20

an antigen-antibody complex

Question 21

why is an antibody specific to 1 antigen only?

Answer 21

the antigen and antibody are proteins with specific tertiary structure. the antibody has binding sites with a specific 3d shape which are complementary to the antigen. The antibody binds to a specific antigen only at its binding site to form an antigen-antibody complex.

Question 22

what are monoclonal antibodies?

Answer 22

identical antibodies produced from a single clone of plasma cells.

Question 23

how can monoclonal antibodies be used in medical diagnosis tools - give and explain 2 examples.

Answer 23

• Prostate cancer - measures levels of specific protein in the blood (levels in blood are high if you have cancer)
• Pregnancy testing - The placenta produces a hormone called hCG that is found in the mother’s urine. Monoclonal antibodies on the pregnancy test’s test strip are linked to coloured particles and if hCG is present the antibodies combine with it and become trapped on the strip, forming a coloured line.

Question 24

how can monoclonal antibodies be used to target medication to specific cell types?

Answer 24

specific cell types have specific antigens on their CSM. a monoclonal antibody for this antigen can be produced. A therapeutic drug can be attached to the monoclonal antibody. The antibody will attach to and deliver the drug to the specific cell type with the complementary antigen only.

Question 25

active immunity | 4 points.

Answer 25

- requires exposure to the antigen - takes longer for immunity to develop - memory cells are produced - protection is long term because the antibody is produced by the organism's own immune system in an immune response.

Question 26

passive immunity | 5 points.

Answer 26

- antibodies are introduced into individuals from an outside source. - there is no exposure to the pathogen/ antigen. - protection is immediate - memory cells are not produced. - protection is short term because antibodies are broken down and cannot be produced by the organism's own immune system

Question 27

How do vaccines work to protect individuals against disease?

Answer 27

- Vaccines contain dead or inactive pathogens with their antigens. - These foreign antigens trigger an immune response, which results in the production of memory cells. (could mention T/ B cells) - Upon reinfection by the same pathogen, memory cells respond by forming plasma cells which rapidly produce antibodies, which cause agglutination and lead to the destruction of pathogens. - herd effect

Question 28

Herd immunity

Answer 28

when a large proportion of the population is vaccinated, the herd effect means that the disease is less likely to be passed on. A susceptible individual is unlikely to come into contact with someone with the disease.

Question 29

Ethics of vaccination

Answer 29

- Millions of lives have been saved - Allowed eradication of smallpox - production/development involves use of animals - Programmes are expensive and the money could be put to better use - Cannot force people to be vaccinated.

Question 30

ethics of monoclonal antibodies

Answer 30

- Production involves use of mice - requires deliberate induction of cancer, which some people may be against due to it causing pain for the mice. - Testing for safety on humans can be dangerous - issues with conduction of drug trials - Can be used successfully to diagnose/treat many diseases

Question 31

structure of HIV

Answer 31

- Attachment proteins embedded in a lipid envelope - The capsid, a protein layer, encloses RNA, of which there are 2 single strands, and enzymes - Reverse transcriptase is one such enzyme and catalyses the production of DNA from RNA. This means HIV is a retrovirus.

Question 32

what does retrovirus mean?

Answer 32

nucleic acid of virus is RNA, from which DNA can be synthesised using reverse transcriptase.

Question 33

Describe how the HIV virus replicates | 9

Answer 33

1. The virus enters the bloodstream and circulates round the body. 2. A protein on HIV binds with a protein (CD4) on TH cells. 3. The capsid fuses with the CSM and the HIV RNA and enzymes enter the cell. 4. HIV reverse transcriptase converts the viral RNA into DNA. 5. The new DNA is inserted into the host cell’s nucleus and DNA. 6. This DNA is used to make HIV mRNA copies 7. mRNA is translated to produce capsid proteins and enzymes at the host's ribosomes. 8. new virus particles are assembled. 9. the new virus particle bud off from the host cell's membrane, taking a piece of its CSM with them to form their lipid envelope.

Question 34

How does HIV cause the symptoms of AIDS?

Answer 34

HIV causes the death of TH cells, reducing their numbers in the blood. This leads to a weakened immune response - B cells are not stimulated to divide and produce antibodies (by TH cells). The person becomes more susceptible to other pathogens. (AIDS)

Question 35

How can AIDS lead to death?

Answer 35

the person's immune system is unable to produce an immune response to pathogens, so they are more susceptible to other pathogens. When a pathogen infects a person, it causes disease by damaging their organs and releasing toxins. The person's immune response isn't strong enough to fight the infection so they die.

Question 36

Does HIV kill?

Answer 36

no, but as it prevents normal functioning of the immune system, those that are HIV +ve can’t respond effectively to other pathogens. This may cause death.

Question 37

What does ELISA stand for?

Answer 37

enzyme-linked immunosorbent assay

Question 38

How can antibiotics work in bacteria and why are antibiotics ineffective against viruses?

Answer 38

Some antibiotics work by preventing bacteria from making normal cell walls - e.g. penicillin. Viruses don’t have their own metabolic pathways or cell structure and rely on host cells to replicate. Antibiotics are therefore ineffective as there are no metabolic mechanisms or cell structures to be disrupted. Viruses also have a protein coat rather than murein cell wall so there aren’t sites where antibiotics can work. In addition, when viruses are in a cell of the host organism, antibiotics cannot reach them.

Question 39

what can the ELISA test be used to do?

Answer 39

detect the presence and quantity of a specific protein in a sample. e.g. detect HIV and the pathogens of other diseases, quantity of antigen and quantities of specific drugs

Question 40

describe how to carry out the ELISA test for a specific antigen (7)

Answer 40

1) Add the sample to a surface - e.g. slide, which antigens can attach to. 2) Wash the surface to remove unattached antigens. 3) Add the antibody specific to the antigen being tested for and leave to bind. 4) Wash again to remove excess antibody. 5) Add a second antibody that binds with the first - this antibody is attached to an enzyme. 6) Add the colourless substrate of the enzyme. The enzyme can act on this substrate to produce a coloured product. 7) The amount of antigen present is relative to the intensity of the colour produced.

Question 41

how are the results of the ELISA test interpreted?

Answer 41

The amount of antigen present is relative to the intensity of the colour produced.