TOPIC 2 - C: cells and immune system

Question 1

Define antigen

Answer 1

Molecules that can generate a immune response when detected by the body

Question 2

Define pathogen

Answer 2

Organisms that causes disease

Question 3

Define abnormal body cells

Answer 3

Cancerous or pathogen-infected cells have abnormal antigens

Question 4

Define toxins

Answer 4

Poisons which are molecules and can be produced by pathogens

Question 5

What happens with blood transfusions?

Answer 5

Cells will have antigens which are different from our own, so this triggers an immune response. This is why blood is matched on ABO blood group

Question 6

Define a phagocyte

Answer 6

A type of white blood cell found in the blood, are the first cells to respond to an immune trigger

Question 7

How does phagocytosis work?

Answer 7

A phagocyte recognises foreign antigens, the cytoplasm engulfs the pathogen so it’s contained in a phagocytic vacuole, a lysosome fuses with the vacuole and the lysozymes break down the pathogen. The phagocyte presents the pathogen’s antigens to active other immune cells

Question 8

What are T-cells?

Answer 8

A white blood cell with receptor proteins that bind to complementary antigens presented by phagocytes

Question 9

What are the 2 types of T-cells?

Answer 9

Helper t-cells (Th) and cytotoxic t-cells (Tc)

Question 10

What do helper t-cells do?

Answer 10

Release chemical signals that activate and stimulate Tc cells and phagocytes. It also activates B-Cells

Question 11

What do cytotoxic t-cells do?

Answer 11

Kill abnormal and foreign cells by releasing a chemical which perforates the CSM, making the cell kill itself

Question 12

What are B-cells?

Answer 12

A white blood cell covered in antibodies, each b-cell has a different antibody on it so they can bind to complimentary antigens to form antigen-antibody complexes

Question 13

What happens during clonal selection?

Answer 13

An antibody on a B-cell binds to a complimentary antigen on a pathogen, activating the B-cell, which divides into plasma cells

Question 14

What do plasma cells do?

Answer 14

Release antibodies specific to the antigen to form antigen-antibody complexes

Question 15

What is agglutination?

Answer 15

Where pathogens become grouped together as antibodies can bind to 2 antigens. Phagocytes engulf many antigen-antibody complexes at once, leading to the destruction of the pathogen

Question 16

What are antibodies?

Answer 16

Proteins, made of chains of amino acids. It’s specific because of the variable regions which form the binding sites, meaning that they have unique tertiary structures. All antibodies have the same constant region

Question 17

What is the cellular (cell mediated) immune response?

Answer 17

• pathogens invade body cells or taken in by phagocytosis
• phagocytes then place antigens from pathogen on the cell membrane
• receptors on specific helper T-cells fit into these antigens
• the attachment activates T-cell to divide rapidly by mitosis and forms a clone of identical cells
• cloned T-cells: develop into memory cells, stimulate B cells, activated cytotoxic T-cells and stimulate phagocytosis

Question 18

What is the humoral response?

Answer 18

• antibodies secreted by plasma B-cells in response to a specific antigen. Each antibody is specific and complementary to one type of antigen
• trial and error to find complementary antibody and antigen
• once the antigen has blinded to corresponding antibody on B cell it enters cell and present on cell surface membrane
• helper T-cells produce cytokines which stimulate specific B cells to divide by mitosis producing monoclonal antibodies

Question 19

What happens during the primary immune response?

Answer 19

A pathogen enters the body for the first time. The primary response is slow because there aren’t enough B-cells to make antibodies needed to bind to the antigens. The infected person will show symptoms. After being exposed to the antigen, memory t-cells (which remember the antigen and will recognise it) and memory b-cells (which remember the antibodies and will make them quicker) are produced, making the person immune

Question 20

What happens during the secondary immune response?

Answer 20

If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. Clonal selection happens faster and antibodies are released sooner. The person won’t show symptoms

Question 21

Define active immunity

Answer 21

When the immune system works to produce its own antibodies after being stimulated by an antigen

Question 22

Give a natural and artificial method of gaining active immunity

Answer 22

Natural - become immune after catching a disease, artificial - become immune after a vaccine

Question 23

Define passive immunity

Answer 23

Being given antibodies made in a different organism

Question 24

Give a natural and artificial method of gaining passive immunity

Answer 24

Natural - when a baby becomes immune due to antibodies received from it’s mother through the placenta and umbilical cord, artificial - become immune after being injected with antibodies from someone else

Question 25

List 3 differences between active immunity and passive immunity

Answer 25

Active immunity: requires exposure to antigen, takes time for protection to develop, memory cells are produced. Passive immunity: doesn't require exposure to antigens, protection is immediate, memory cells aren't produced

Question 26

How do vaccines work?

Answer 26

- antigens injected into blood which stimulates a primary immune response, producing antibodies - memory cells are produced - on second exposure they rapidly divide into plasma cells which rapidly proceed antibodies against the pathogen - pathogen destroyed before symptoms

Question 27

Define herd immunity

Answer 27

Those who are vaccinated are likely to protect those not vaccinated, as there's less chance of the disease occurring

Question 28

What are the disadvantages of taking a vaccine orally?

Answer 28

It could be broken down by enzymes in the gut or the molecules could be too large to be absorbed into the blood

Question 29

Why are booster vaccines given?

Answer 29

To make sure that more memory cells are produced and that the person is immune

Question 30

What are some of the ethical issues surrounding vaccines?

Answer 30

All vaccines are tested on animals, which people disagree with. Testing on humans can be risky, volunteers may put themselves at unnecessary risk to prove that it works. If there was an epidemic of a new disease, people would rush to get a vaccine, and decisions would have to be made on who would be the first to get it

Question 31

What is antigenic variation?

Answer 31

Where pathogens change their surface antigens so the immune system doesn't recognise the antigens, so memory cells won't work, even if you're infected with the same disease

Question 32

Why does the influenza vaccine change every year?

Answer 32

This is due to antigenic variation. The antigens on the surface change regularly, resulting in constant vaccines as every year, there's a different strain

Question 33

What can monoclonal antibodies be used for?

Answer 33

Medical diagnoses and pregnancy tests

Question 34

How do pregnancy tests work?

Answer 34

They detect hCG in urine of pregnant women. The application area contains antibodies bound to a blue bead that are complimentary to the hCG protein, when urine is applied, hCG will bind to the antibodies, forming an antigen-antibody complex. The urine moves up the stick, carrying blue beads with it. The test strip contains immobilised amtibodies to hCG which bind to hCG if its detected, turning the strip blue, confirming pregnancy

Question 35

What does the ELISA test detect?

Answer 35

Enzyme-Linked ImmunoSorbent Assay (ELISA) looks for specific antigens/antibodies. It can test for HIV/AIDS and allergies

Question 36

Outline the direct ELISA test

Answer 36

Antigens form a patient sample is bound to a well in a well plate. A detection antibody that is complimentary to the antigen of interest is added. If the antigen is present, the antibody is immobilised, the well is washed to remove unbound antibodies. A substrate solution is added, and if the detection antibody is present, the enzyme reacts with the substrate to give a colour change

Question 37

Outline the indirect ELISA test to diagnose HIV

Answer 37

The antigen is bound to a well, the sample of blood is added to the well so any antibodies for HIV can bind to the antigens. The well is washed out to remove unbound antibodies. A secondary antibody is added which binds to the HIV antibody, the well is washed again. A substrate solution is added to the well which will react with the enzyme on the secondary antibody if any remains, indicating the patient has HIV

Question 38

Indicate ethical issues surrounding the use of monoclonal antibodies

Answer 38

Animals are used to produce the cells from which the monoclonal antibodies are produced, some people disagree with this

Question 39

What is HIV?

Answer 39

Human Immunodeficiency Virus attacks the body's immune system. It eventually leads to AIDS (Acquired Immune Deficiency Syndrome), where the immune system eventually fails and you die from complications

Question 40

How does HIV work?

Answer 40

It attacks Th cells, which act as the host cell for the virus. Th cells activate phagocytes, Tc cells and B cells, so those cells won't work, meaning an immune response can't be triggered

Question 41

What happens during the initial infection period of HIV?

Answer 41

HIV replicates rapidly and the person may suffer extreme flu-like symptoms. After this, replication drops to a lower level, known as the latency period, where the person won't experience symptoms

Question 42

What are the symptoms of AIDS?

Answer 42

People are classed as suffering with AIDS when their white blood cells drop below a certain level. The initial symptoms are minor infections of mucus membranes and recurring respiratory infections. As it progresses, the immune cells decrease, so they become more susceptible to severe bacterial infection and TB. During the late stages, people have very low immune cell levels, so can develop toxoplasmosis of the brain and candidasis of the repsiratory system.

Question 43

What is the structure of HIV?

Answer 43

Has a spherical structure, made up of a core of RNA and proteins (including reverse transcriptase), a capsid, attachment proteins and an envelope made of membrane stolen from a previous host cell

Question 44

How does HIV replicate?

Answer 44

- viral attachment protein attaches to a receptor molecule on the cell membrane of host helper T-cell - capsid is released into cell where it uncoils and releases RNA into cells cytoplasm - reverse transcriptase used to make complementary strand of DNA from RNA - double stranded DNA is made from this which is inserted into human DNA - enzymes in cell used to make viral proteins from viral DNA - they're assembled into new viruses which bud from the cell and infect other cells

Question 45

How do antibiotics kill bacteria?

Answer 45

They interfere with metabolic reactions by targeting enzymes and ribosomes.

Question 46

Why can't antibiotics kill viruses?

Answer 46

They don't have their own enzymes and ribosomes, they use host cell enzymes

Question 47

How can HIV be controlled?

Answer 47

Reduce the spread, always have protected sex and not sharing needles