Cell Recognition And The Immune System

Question 1

Each cell has what that identifies it

Answer 1

Specific molecules that are proteins on its surface

Question 2

What do the surface molecules enable the immune system to identify

Answer 2

Pathogens, non self material (cells from organisms of the same species), abormal body cells like cancer cells and toxins

Question 3

What are examples of non specific defence mechanisms

Answer 3

Physical barriers like skin and phagocytosis

Question 4

Describe the process of phagocytosis

Answer 4

1. A phagocyte is attracted to the chemical products of a pathogen and move towards the pathogen. 2. Phagocytes have receptors on their cell surface membrane which recognise and attach to chemicals on the pathogen’s surface 3. The phagocyte engulfs the pathogen to form a phagosome (vesicle) 4. Lysosomes within the phagocyte move to the phagosome and fuse with it 5. Lysosomes release their lysozymes into the phagosome which destroy inhested bacteria by hydrolysis of their cell walls 6. Soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte

Question 5

Define antigen

Answer 5

Any part of an organism / MOLECULE that is recognised as non self by the immune system and stimulates an immune response

Question 6

The difference between b and t lymphocytes

Answer 6

B cells mature in bone marrow and are involved with humoral immunity and T cells mature in the thymus gland and are associated with cell mediated immuntiy

Question 7

Describe the process of cell mediated immunity

Answer 7

1. Pathogens invade body cells/ are taken in by phagocytes 2. The phagocyte places antigens from pathogen on it’s cell surface membrane 3. Receptors on a specific helper T cell bind to the complementary antigen on the APC 4. This attachment activates the T cell to divide rapidly by mitosis to form a clone of genetically identical cell 5. The cloned T cells: develop into memory cells (enable rapid response to future infection by same pathogen), stimulate phagocytosis, stimulate b cells to divide & secrete antibodies and activate cytotoxic T cells (produce perforin to perforate cell surface membrane, causing cell to die/lyse)

Question 8

Describe the process of humoral immunity

Answer 8

1. The surface antigens of an invading pathogen are taken up by a B cell 2. The B cell processes the antigens and presents them on it’s surface 3. Activated helper T cells attach to the processed antigens, activating the B cell 4. Activated B cell divides by mitosis to give a clone of plasma cells 5. Cloned plasma cells produce and secrete complementary antibody to antigen and attaches and destroys them 6. Some B cells develop into memory cells which respond to future infection (by same pathogen) by dividing RAPIDLY and developing into plasma cells that produce antibodies (2ndary response)

Question 9

Antibody definition

Answer 9

Proteins with specific binding sites, synthesised by B cells

Question 10

Describe the structure of an antibody

Answer 10

Made up of 4 polypeptide chains, chains of one pair are heavy chains, chains of other are light chains. Each has 2 binding sites, complementary to a specific antigen which bind to form and antigen- antibody complex. The binding site the the variable region, the rest is the constant region

Question 11

How does an antibody show quarternary structure

Answer 11

Has more than one/ has 4 polypeptide chains

Question 12

How does an antibody show tertiary structure

Answer 12

Each binding site consists of a sequence of amino acids that form a specific 3D structure/shape that is complementary to a specific antigen

Question 13

How do antibodies lead to the destruction of antigens

Answer 13

They cause agglutination where clumps of cells are formed, making it easier for phagocytes to locate them as they are less spread out. They then serve as markers that stimulate phagocytosis of cells to which they are attached

Question 14

Monoclonal antibody definition

Answer 14

Antibodies with with same tertiary structure and are all specific to the same antigen produced from a genetically indentical set of plasma cells

Question 15

Describe use of monoclonal antibodies in targeting medication to specific cellswith theraputic drugs

Answer 15

1. Monoclonal antibodies are produced that are specific to antigens on cancer cells 2. Antibodies given to patient and attach themselves to receptors on cancer cells and block the chemical signals that stimulate their uncontrolled growth ( example herceptin)

Question 16

Advantages of monolconal therapy

Answer 16

Fewer side effects as antibodies aren’t toxic and are very specific

Question 17

Describe indirect monoclonal antibody therapy, describe benefits

Answer 17

Attaching a radioactive or cytotoxic drug to monoclonal antibody which attaches to cancer cells and kills them. Less side effects and cheaper as can be used in small doses as are specific

Question 18

Describe the use of monoclonal antibodies in medical diagnosis

Answer 18

Used to diagnose prostate cancer as patients produce more of the prostate specific antigen protein. Using a monoclonal antibody that interacts with the antigen means you can obtain a measure of the level of psa in a sample of blood

Question 19

Describe how a pregnancy test works

Answer 19

HCG is a hormone produced by the placenta and is present in the mother’s urine. The test strip contains mobile HCG monoclonal antibodies with coloured particles attached. The urine travels up the wick and HCG binds to the antibodies, creating HCG- antibody complex. This moves up and is trapped by immobile antibodies, creating a coloured line. Spare antibodies bind to more immobile antibodies to give a control

Question 20

Ethical issues of using monoclonal antibodies

Answer 20

1. New monoclonal antibody therapies often test on animals 2. Animals are used to produce antibodies and tumor cells 3. Some deaths have been associated with treatments 4. Human testing for new drugs may be dangerous

Question 21

What is active immunity and examples

Answer 21

Stimulating the production of antibodies by an individual’s own immune system. Being infected with a disease or vaccination

Question 22

What is passive immunity and examples

Answer 22

Introduction of antibodies into an individual from an outside source examples ars antivenom and the antibodies in a fetus from the mother via the placenta

Question 23

differences between active and passive immunity

Answer 23

• active immunity involves memory cells, passive doesn’t - immunity is acquired instantly in passive, takes longer to develop in active

Question 24

Vaccine definition

Answer 24

The introduction of antigens to the body to stimulate an immune response to a particular disease so memory cells are produced which remain in the blood to respond to future infection

Question 25

What are the features of a sucessful vaccination programme

Answer 25

1. Few side effects. 2. Means of storage and transportation 3. Means of administering 4. Enough for majority of vulnerable population to produce herd immunity

Question 26

What is herd immunity

Answer 26

When a sufficiently large portion of the poluation has been vaccinated to make it difficuit for a pathogen to spread within the population

Question 27

Why vaccination may not eliminate a disease

Answer 27

1. May fail to induce immuntiy for those with defective immune systems 2. May develop disease right after vaccination 3. Pathogen may mutate frequently (antigenic variability) 4. Too many varieties of pathogen 5. Objections to vaccine

Question 28

Ethical issues of using vaccines

Answer 28

Use of animal testing, human trials, side effects

Question 29

Describe HIV structure

Answer 29

On the outside there is a lipid envelope, imbedded with attachment proteins. Inside there is the capsid that encloses rna and the reverse transcriptase enzyme

Question 30

Why is hiv classed as a retrovirus

Answer 30

As it has the reverse transcriptase enzyme which catalyses production of dna from rna

Question 31

How is HIV replicated in helper T cells

Answer 31

1. Hiv enters the bloodstream and circulates the body 2. Protein on hiv binds to the CD4 protein, mostly found on helper T cells 3. The capsid fuses with the cell surface membrane and the rna& enzymes in hiv enter the helper T cell 4. The reverse transcriptase converts the virus’s rna into dna 5. The dna moves into the helper T cells nucleus and dna 6. The hiv dna creates mRNA using the cells enzymes which contains info for making viral dna and proteins 7. mRNA passes out of the nucleus & uses cells protein synthesis to make hiv particles 8. Particles break away from T cell with a piece of its membrane

Question 32

How does HIV cause the symptoms of aids

Answer 32

Hiv causes aids by killing and interfering with normal helper T cells, without enough helper T cells the immune system can’t stimulate B cells to produce antibodies and cytotoxic T cells. Also memory cells may be affected so body can’t stimulate immune response so the individual is susceptible to infections and cancers

Question 33

Why are antibiotics ineffective against viruses

Answer 33

One way antibiotic work is by preventing bacteria from creating cell walls which makes them unable to withstand pressure so the cell bursts but they are ineffective as viruses lack their own cell structures and no cell wall

Question 34

How are antibodies used in the ELISA test

Answer 34

1. Apply sample to surface where all antigens in sample will attach 2. Wash surface to remove unattached antigens 3. Add complementary antibody to antigen and leave to bind 4. Wash to remove excess antibody 5. Add 2nd antibody with enzyme attached that binds with first 6. Add colourless substrate (enzyme acts to change it to a coloured product) 7. Amount of antigen relative to intensity of colour

Question 35

Describe the effect of antigenic variability

Answer 35

It’s when antigens on a pathogens surface change due to mutation ( change in primary therefore specific tertiary structure)so they are no longer recognised and antibodies no longer bind so antibodies aren’t produced to destroy the pathogen

Question 36

The differences between a primary and secondary immune response

Answer 36

Secondary= more antibodies produced, antibodies produced quicker, level of antibodies remains for longer

Question 37

People with aids die because they are unable to produce an immune response to pathogens, explain why this leads to death

Answer 37

They are susceptible to other pathogens which reproduce in the host cells which causes cell damage and toxins are released

Question 38

Why does HIV rapidly entering host cells mean a vaccine may be ineffective

Answer 38

HIV enters cells before antibodies can attach/destroy the HIV as they cannot enter cells

Question 39

Pathogen definition

Answer 39

Organism that causes disease/ immune response

Question 40

What does attenuated mean

Answer 40

The microorganism is alive/active but does not cause symptoms of the disease