Cell recognition and the immune system

Question 1

Define pathogen

Answer 1

Micro-organisms that cause diseases

Question 2

Define antigen

Answer 2

A foreign protein that stimulates an immune response causing production of antibodies

Question 3

Give examples where antigens can be found

Answer 3

Pathogens, toxins, cells from other organisms of the same species, mutated cells ( abnormal cells ), bacteria

Question 4

Define antibody

Answer 4

A protein, produced by lymphocytes; in response to the presence of an appropriate antigen

Question 5

Define immune system

Answer 5

A system of biological structures and processes that identifies and kills pathogens ( and tumour cells )

Question 6

What are the stages of defence

Answer 6

1) Prevent invasion
2) Non-specific - phagocytes
3) Specific - lymphocytes

Question 7

Describe phagocytosis

Answer 7

• Phagocyte attracted to pathogen by chemicals/ recognise antigens on pathogen as non-self
• Phagocyte engulfs the pathogen
• The pathogen in membrane bound pocket called a phagosome
• Lysosomes fuse with the phagosome and release digestive ( hydrolytic) enzymes into phagosome
• The enzyme digest ( hydrolyse) the pathogen, destroying it
• ## Antigens from the pathogen are displayed on the surface membrane

Question 8

What two types of cell mediated immunity response

Answer 8

1) Cell- mediated - response by T-lymphocytes
2) Humoral - response by B-lymphocytes

Question 9

Why are cell mediated responses more specific than phagocytosis

Answer 9

Each pathogen has a specific shaped antigen on its surface. These are different for different types or species of pathogens

Question 10

Why are cell mediated responses slower than phagocytosis

Answer 10

Specific lymphocytes exist in the body already, there are millions of different types which each recognise a different antigen. They have proteins ( receptors) on the surface that binds to the proteins ( antigens) recognised as foreign on a pathogen

Question 11

What cells can display the antigens of non-self antigens on their surface and what are they called collectively

Answer 11

1) Phagocytes
2) Body cells invaded by viruses
3) Cancer cells
4) Transplanted cells
Know as - antigen presenting cells ( APC)

Question 12

Describe cell-mediated response

Answer 12

1) The receptor on a T cell binds to antigens present on body cells
2) It activates other cells to divide rapidly by mitosis ( clonal selection)
3) These cloned T cells take one of 3 roles
- Helper cell : Secret cytokinesis which stimulates phagocytosis/ B-lymphocytes to mitosis
- T-cytotoxic cells : Secret hydrogen peroxide to destroy body infected cells
- T-memory cells : Remain in the body for many years

Question 13

What type of pathogen are T-cells most effective against and why

Answer 13

Viruses because they invade/ inside body cells

Question 14

Define differentiation

Answer 14

Permanent change that occur in a cell when it specialised

Question 15

Describe humoral immunity

Answer 15

1) Plasma B cells produce antibodies
2) Different shaped antibodies are produced by different B cells
3) B cells have surface receptors that are the same shape as the antibody that they make
4) Surface receptors are complementary to specific antigens

Question 16

Describe the structure of an antibody

Answer 16

1) Antibodies are proteins
-2)They are made up of 4 polypeptide chains:
- 2 long, heavy chains
- 2 short, light chains
3) The variable region is specific to an antigen

Question 17

Define monoclonal antibodies

Answer 17

Antibodies made from hybridoma which all the antibodies are the same

Question 18

What is agglutination

Answer 18

Antibodies causes microbes to stick together. This makes it easier for phagocytes to engulf them

Question 19

Why are antibodies made from proteins

Answer 19

Structure allows infinite number of forms

Question 20

How does monoclonal antibodies help treat cancer

Answer 20

Monoclonal antibodies specific to antigens on a cancer cell are produced. Antibody binds to cancer cell and block the chemical signal that stimulates growth. Or, a radioactive or cytotoxic drug is attached to the antibody. When the antibody binds to the receptor on the cancer cell, the cell is killed.

Question 21

How does monoclonal antibodies used in chemical diagnosis

Answer 21

Using antibodies that are complementary to specific pathogens or toxins in the blood to detect their presence. E.G Influenza

Question 22

How are monoclonal antibodies used in pregnancy tests

Answer 22

1) Potential mother urinates on chromatography paper
2) Chromatography paper contains free HCG antibodies with attached coloured particles
3) If HCG is present, it will bind to the complementary antibodies and move up the chromatography paper
4) HCG- antibody complexes with the dye bind to a fixed HCG antibodies
5) Build up in the test area causes a coloured band to appear ( positive test)
6) No HCG present then the free antibodies flow past the fixed HCG antibodies
7) There is no build up of dye, so no colour appears ( negative test)

Question 23

What is a vaccination

Answer 23

Contains an antigen that stimulates the production of antibodies

Question 24

What is an attenuated microorganism

Answer 24

A microorganism that is alive but does not cause any symptoms

Question 25

What is herd immunity

Answer 25

Stops infection spreading

Question 26

Describe how a vaccination can lead to the production of antibodies against a specific pathogen

Answer 26

1) Vaccine contains antigen ( from specific pathogen) 2) Displayed on antigen-presenting cells 3) Specific helper T cell detects antigen and stimulates specific B cells 4) B cell divides and forms clones to give plasma cells 5) Plasma cells produce antibodies

Question 27

What is active immunity

Answer 27

Your immune system makes its own antibodies after being stimulated by antigens

Question 28

What is passive immunity

Answer 28

Antibodies are made by another organism and then given to you

Question 29

What are some examples of natural immunity

Answer 29

- Through the placenta and breast milk - Catching the disease

Question 30

What are some examples of artificial immunity

Answer 30

- Injected with antibodies from someone else - Being vaccinated

Question 31

What are the differences between active and passive immunity

Answer 31

1) Active- You make your own antibodies by plasma cells. Passive- An organisms antibodies are giver to you 2) Active- Slower Passive- Faster 3) Active- Involves memory cells Passive- Doesn't involve memory cells 4) Active- Long term Passive- Short term

Question 32

What are the ethical issues of vaccines

Answer 32

- Testing on animals - Testing on humans is risky - Some people do not want to take the risk of side effects of using vaccines - Who would get vaccine first?( the rich or the poor)

Question 33

What are the ethical issues of monoclonal antibodies

Answer 33

- Animal testing, animals will die - Animals used to produce the tumour cells- involves giving cancer in mice - Testing on humans

Question 34

Describe and explain the structure of HIV

Answer 34

1) Attachment proteins- Allows the virus to attach to host cells 2) Matrix- Main body of the virus 3) Reverse transcriptase- An enzyme that catalyse the production of cDNA from RNA 4) Lipid envelope- Surrounds the virus that contains attachment proteins 5) Capsid- Encloses the genetic material 6) RNA- The genetic material

Question 35

Describe HIV

Answer 35

- Smaller then bacteria - Contains nucleic acids ( RNA) - Can only multiply inside living hosts - Attachment proteins on the lipid envelope allows the virus to identify and attach to a host cell

Question 36

How does HIV replicate?

Answer 36

- HIV enters the bloodstream - A protein on HIV readily binds to a protein called CD4 on helper T cell - The capsid fuses with the T cell membrane. RNA and enzymes of HIV enter helper T cell - Reverse transcriptase converts RNA into cDNA - The cDNA is inserted into the helper T cell - DNA transcribed into HIV mRNA - HIV mRNA translated into new HIV proteins for assembly into viral particles - HIV particles break away from the T cell with a piece of its cell membrane, forming its own lipid envelope

Question 37

Describe dormancy

Answer 37

- This process of HIV replication continuous for a few weeks, before the HIV virus goes into dormancy in the T helper cell - Antibodies against HIV virus still circulates, and this is how someone can be said to be HIV positive

Question 38

Describe ELISA ( enzyme-linked immunosorbent assay)

Answer 38

1) The HIV antigens applied to a surface, the HIV antigens would stick 2) Surface is washed to remove any unattached antigen 3) The sample is added and give time to bind if antibodies are present 4) Surface is washed to remove any unattached antibodies 5) A second antibody ( with an enzyme attached) is added, which is complementary to the first antibody. These bind together 6) Surface is washed to remove any unattached second antibody 7) A colourless substrate to the enzyme is added. The enzyme breaks down the substrate into coloured products 8) The amount of antigens present is related to the colour intensity