Unit 2 - Cell Recognition + The Immune System

Question 1

What is an antigen?

Answer 1

A foreign molecule that stimulates an immune response. They are often proteins or glycoproteins.

Question 2

Definition of foreign?

Answer 2

In biology, foreign means something which is not part of the host organism (your own body).

Question 3

Antigens enable the immune system to identify what cells and molecules?

Answer 3

-Pathogens
-Abnormal body cells, e.g. cancer cells + infected cells
-Toxins
-Cells from other individuals of the same species.

Question 4

What are pathogens?

Answer 4

Pathogens are microorganisms that cause disease, e.g. bacteria, fungi + viruses.

Question 5

How do pathogens cause disease?

Answer 5

By damaging/killing cells and tissues and producing toxins.

Question 6

What are phagocytes?

Answer 6

White blood cells that carry out phagocytosis, which involves engulfing the foreign antigen.

Question 7

What is the 1st stage of the immune response and why is it nonspecific?

Answer 7

Stage 1 = Phagocytosis.
It is nonspecific because phagocytes will engulf anything foreign.

Question 8

Steps of phagocytosis?

Answer 8

1) Phagocyte recognises the antigen as foreign.
2) The pathogen is engulfed by the phagocyte.
3) Engulfed pathogen is contained inside a vesicle called a phagosome.
4) Lysosomes fuse with the phagosome releasing lysozymes into the phagosome.
5) Lysozyme enzymes hydrolyse the molecules, e.g. proteins in the pathogen.
6) The antigens from the pathogen are presented on the cell surface membrane of the phagocyte - the phagocyte becomes an antigen presenting cell.

Question 9

Acronym to remember phagocytosis?

Answer 9

Phagocyte
Recognises foreign antigen
Engulfs antigen
Phagosome
Fuses (lysosome)
Enzymes (lysozymes)
Hydrolyse
Antigen presented
Membrane
Acronym=Penis Reaches Extreme Places for Extreme Happiness A-Men.

Question 10

What is the 2nd stage of the immune response?

Answer 10

Specific immune response. It would take too long to destroy a pathogen using only just phagocytosis, so a specific response is initiated where a specific foreign antigen is targeted.

Question 11

What are helper t-cells?

Answer 11

White blood cells that have protein receptors in their cell membrane.

Question 12

How are t-cells activated?

Answer 12

Helper t-cell with specific complementary receptor, binds to antigen on antigen presenting cell and the t-cell is activated.

Question 13

The activated t-cell then releases chemical signals (cytokines) which further activates what?

Answer 13

-More phagocytes.
-Cytotoxic t-cells which kill infected cells directly.
-Specific B-cells also a type of white blood cell.

Question 14

What is part 1 of stage 2?

Answer 14

The cellular response - T cells.

Question 15

Acronym for cellular response (t-cells)?

Answer 15

An antigen presenting cell
Activates
Specific
T-cell
Clones (mitosis)
Cytotoxic t-cells
Helper T cells
Stimulating
B-cells
Phagocytes
Acronym = An Awesome Shag Touches Clit Carefully He Should Be Proud

Question 16

What is part 2 of stage 2?

Answer 16

Humoral response - B cells.

Question 17

How are specific b cells activated?

Answer 17

By their specific helper T cell.

Question 18

What is the humoral response?

Answer 18

1) Specific B cells are activated by their specific helper T cell.
2) B cells clone into memory cells and plasma cells.
3) Plasma cells secrete specific antibodies which bind the foreign antigen.

Question 19

Acronym for the humoral response?

Answer 19

T helper cell (specific)
Activates
B cell (specific)
Clones by mitosis
Plasma cells
Antibodies
Memory cells
Acronym = To Activate Boner Chew Penis All Morning.

Question 20

What do plasma cells release?

Answer 20

Many monoclonal antibodies which have binding sites complementary to the same antigen and bind, leading to the destruction of the pathogen through agglutination and phagocytosis.

Question 21

Definition of monoclonal antibodies?

Answer 21

Antibodies with the same tertiary structure, which are complementary to and bind one type of antigen. They come from the same type of B cell.

Question 22

What is the primary immune response?

Answer 22

Helper T cells activating B cells to result in antibody production. This occurs each time you come across a new antigen that you have not been exposed to before.

Question 23

What is the secondary immune response?

Answer 23

Memory B cells have an antibody with the same tertiary structure, complementary to the same antigen as the parent B cell. So if re-infected with the same antigen, memory B cells with the complementary antibody:
-bind the antigen
-clone into plasma cells
-produce many more antibodies, more quickly to kill the foreign cell.

Question 24

Structure of an antibody?

Question 25

Describe the structure of an antibody?

Answer 25

They have a quaternary structure made up of 4 polypeptide chains, 2 heavy chains and 2 light chains, held together by disulphide bridges. It’s a protein!

Question 26

What are the 2 regions in an antibody?

Answer 26

Constant region = has the same tertiary structure in all antibodies. Variable region = contains the binding site for antigens and differs between antibodies making antibodies complementary to only one type of antigen.

Question 27

When an antibody binds to an antigen it is known as?

Answer 27

An antigen-antibody complex.

Question 28

What is agglutination?

Answer 28

Antigen-antibody complexes cause the foreign cells to clump together as each antibody has 2 binding sites, which can bind to 2 antigens at the same time on different cells. This allows many cells to be engulfed by a phagocyte in one go.

Question 29

Summary of the immune response? (Use this to answer 5 mark questions on the primary immune response)

Answer 29

1) A phagocyte engulfs the pathogen, hydrolyses it and presents antigens on its surface membrane. 2) Specific helper T cell with a complementary receptor protein binds to the antigen. 3) This helper T cell binds to and activates a specific b cell. 4) The specific b cell clones by mitosis into plasma cells which make and secrete many antibodies with specific binding sites complementary to the antigen. 5) The antibodies agglutinate the antigens, which are destroyed by phagocytes. 6) Memory b cells with the complementary antibody remain and clone into plasma cells when presented with the same antigen, producing many more antibodies, faster.

Question 30

Primary and secondary response graph?

Question 31

Why do symptoms occur in the primary response?

Answer 31

Because when the antigen infects the body for the first time antibodies are produced more slowly and there are less of them as it takes time for clonal selection (the process by which a specific b cell is stimulated to clone) to occur so symptoms occur.

Question 32

Why do symptoms not occur in the secondary response?

Answer 32

Clonal selection occurs more quickly (because phagocytosis, antigen presentation and helper T cell activation is not required) and the plasma cells produce many more antibodies at a faster rate so the infection is overcome before any symptoms can occur.

Question 33

Overall how do vaccines work?

Answer 33

By creating a primary response against an antigen so that memory b cells are formed with complementary antibodies to the antigen, without the symptoms of the pathogen itself.

Question 34

How do vaccines work?

Answer 34

1) vaccines contain antigens from the pathogen. 2) a phagocyte (macrophage) engulfs the antigen and presents it on its surface membrane. 3) a specific helper T cell with a complementary receptor protein binds to the antigen. 4) this helper T cell stimulates a specific b cell which divides by mitosis. 5) the b cells clone into plasma cells which produce and secrete many antibodies with specific binding sites complementary to the antigen. The antibodies agglutinate the antigen and destroy it. 6) memory b cells are produced so on a second exposure to the antigen more antibodies are produced more quickly, destroying the pathogen before symptoms are displayed.

Question 35

Why sometimes are booster vaccines given out?

Answer 35

To increase the number of memory cells over a long period of time.

Question 36

What is herd immunity?

Answer 36

If a majority of the population are vaccinated then most people cannot get the disease. Therefore, those who are not vaccinated are also protected as there are less people to transmit the disease.

Question 37

What are ethical issues with vaccines?

Answer 37

-Development and testing may involve use of animal and it may cause some pain/suffering to the animals and a large number may be used. -Human testing. Volunteers used for testing may be put at risk. -The vaccine may have side effects. The risk and severity of these side effects can vary between vaccines. -People may not have the vaccine due to risk of side effects and instead rely on herd immunity for protection. Is this fair to those who have had the vaccine? -Who should receive a new vaccine first? -Should all people be forced to have the vaccine if it benefits society even if certain groups may not agree with the vaccinations?

Question 38

What is antigenic variability?

Answer 38

Due to mutations in the DNA of pathogens, the tertiary structure of the antigen protein can change shape.

Question 39

How does antigenic variability cause a secondary response to not occur?

Answer 39

If a pathogen, which has previously infected the body, is encountered again with a changed antigen, the antigen binding site of antibodies from the memory cells will not be complementary and a secondary response does not occur. The patient will have to carry out the primary response again and experience the symptoms again.

Question 40

How does antigenic variability cause vaccines to become ineffective?

Answer 40

The antibodies produced as a result of the vaccine are no longer complementary. A new vaccine needs to be made each time the antigen changes which takes time and is expensive.

Question 41

What is active immunity?

Answer 41

Following exposure to an antigen, specific memory B cells are made which produce antibodies against antigen. Natural - immune after actually having the disease. Artificial - immune after given vaccination.

Question 42

Advantages of active immunity?

Answer 42

Long term protection as memory cells are made.

Question 43

Disadvantages of active immunity?

Answer 43

-Artificial can only be given before getting the disease. -Takes more time before immune, to make memory cells. -Natural will get symptoms of the disease.

Question 44

What is passive immunity?

Answer 44

Antibodies against the antigen are put straight into the body, the immune system does not make the antibodies. Natural - a baby receives antibodies from its mother’s milk. Artificial - injected with antibodies made in a lab.

Question 45

Advantages of passive immunity?

Answer 45

-Can be given after exposure to antigen/pathogen. -Works straight away.

Question 46

Disadvantages of passive immunity?

Answer 46

Does not last long as antibodies broken down, no memory cells are produced.

Question 47

How are monoclonal antibodies used in treating diseases, I.e. cancer?

Answer 47

-Cancer cells have unique antigens on their cell membrane which normal body cells do not have. -Monoclonal antibodies, which have an anti-cancer drug attached, can be made complementary to the cancer cell antigen. -The monoclonal antibodies bind only to the cancer cells, killing them, reducing the side effects of the drug as fewer healthy cells are damaged.

Question 48

What protein is found in the urine of pregnant women?

Answer 48

hCG - human chorionic gonadotropin

Question 49

How are monoclonal antibodies used in pregnancy tests?

Answer 49

-The test strip on the pregnancy tests contains an hCG monoclonal antibody with a coloured dye attached. -Urine flows along the test strip and any hCG in the urine binds the monoclonal antibody. -The hCG-antibody complexes then flow into the test area when there are fixed hCG antibodies. -The hCG-antibody complexes with the dye bind the fixed hCG antibodies and build up on the test line concentrating the dye. This causes the coloured band to appear (positive result). -If there is no hCG present then the hCG antibodies antibodies flow past the fixed hCG antibodies on the test line and bind to the fixed antibodies on the control line. -The antibodies fixed to the control line are complementary to the hCG antibody, not the hCG itself. -The colour of the test line changes, showing the test has worked correctly, but as there is only one coloured line, and not two, it is a negative result.

Question 50

How are monoclonal antibodies used to diagnose disease using tissue samples?

Answer 50

Monoclonal antibodies complementary to the antigens on cancer cells can be used in cancer diagnosis on biopsy tissue samples. The antibody complementary for the cancer antigen has a fluorescent tag on it which shows up down a microscope.

Question 51

What is ELISA (Enzyme Linked ImmunoSorbant Assay)?

Answer 51

ELISA uses monoclonal antibodies to detect the presence of a certain antibody or antigen in the body. This is used to determine if an individual has a disease or not.

Question 52

Specific antigens indicate what?

Answer 52

The presence of a pathogen.

Question 53

Antibodies indicate the presence of what?

Answer 53

That the person has been exposed to the pathogen which has stimulated an immune response.

Question 54

Indirect ELISA is used to?

Answer 54

Detect an antibody.

Question 55

Direct ELISA is used to?

Answer 55

Detect the presence of antigens, instead of antibodies.

Question 56

Steps of the ELISA process?

Answer 56

1) The antigen is bound to the bottom of a plastic well. 2) A sample is added to the well. If any antibodies against the pathogen are present then the antibody binds to the antigen. Well is washed to remove any unbound antibodies. 3) A second antibody, complementary to the first antibody, is added. This antibody has an enzyme attached to it. 4) The well is washed again to remove any unbound enzyme-linked antibody. This is very important as this produces a negative result if no antibodies are present in the person’s sample. If it was not washed then a false positive would occur (there would be a colour change) as the enzyme is present. 5) A solution is added to the well which contains a substrate. The enzyme on the 2nd antibody reacts with the substrate, producing a colour change, which is a positive result for the presence of the antibody.

Question 57

What is HIV?

Answer 57

HIV = human immunodeficiency virus. It’s a retrovirus which infects and kills helpers T-cells, reducing the effectiveness of the immune response.

Question 58

Structure of HIV?

Question 59

Attachment protein?

Answer 59

Attaches virus to complementary receptor on host helper T cell.

Question 60

RNA?

Answer 60

Genetic material of HIV.

Question 61

Reverse transcriptase?

Answer 61

Enzyme which converts RNA into DNA in host cell.

Question 62

Capsid?

Answer 62

Made of protein.

Question 63

Lipid envelope?

Answer 63

Outer layer made of membrane taken from previous host cell.

Question 64

Replication of HIV?

Answer 64

1) The attachment protein on HIV binds to a complementary receptor on the helper T-cell. 2) The capsid enters the cell and releases the RNA into the cytoplasm. 3) Reverse transcriptase makes DNA from the HIV RNA. 4) Using the host cells enzymes and ribosomes for protein synthesis, viral proteins are made from the DNA. 5) New virus particles are formed from the proteins which bud from the cell and infect more Helper T cells.

Question 65

A VIRUS has a CAPSID! PROKARYOTES have a CAPSULE!

Question 66

What does AIDS stand for?

Answer 66

Acquired Immune Deficiency Syndrome.

Question 67

What happens when helper T-cell numbers become very low?

Answer 67

The immune system starts to fail and serious infections can kill the patient.

Question 68

When is AIDS clinically diagnosed?

Answer 68

When the T cell number drops below 200 per ml of blood.

Question 69

What do antibiotics treat?

Answer 69

They only kill bacteria and not viruses.

Question 70

Why do antibiotics only kill bacteria?

Answer 70

Because they target parts of a bacteria which are not found in a virus, i.e. the bacterial cell wall, ribosomes and bacterial enzymes.

Question 71

Why are viruses difficult to kill?

Answer 71

Because they replicate inside cells and have very few drug targets such as enzymes, as they use the host cells’ enzymes and organelles for replication.

Question 72

What is one target for antiviral drugs?

Answer 72

The viral reverse transcriptase, but this only works if it’s a retrovirus (reverse transcriptase inhibitors) which contains the reverse transcriptase.

Question 73

Why do antibiotics not kill human cells?

Answer 73

Because bacterial enzymes and ribosomes (70s in bacteria and 80s in eukaryotic) are different in each.

Question 74

How can you prevent the spread of HIV?

Answer 74

-Protected sex. -Using clean sterilised needles. -HIV positive mothers take anti-retroviral drugs during pregnancy to reduce chance of giving baby HIV.

Question 75

What are some examples of aseptic techniques?

Answer 75

-Wash hands with soap -Disinfect surfaces -Use sterile pipette/syringe to transfer bacteria -flame neck of bottle -lift lid of agar plate at an angle -work close to upward air movement -use sterile spreader -place pipette/spreader into disinfectant (immediately after use)