Cell Recognition And The Immune System

Question 1

What does the reverse transcriptase enzyme do?

Answer 1

Catalyse the conversion of RNA -> DNA

Question 2

How does HIV replicate?

Answer 2

HIV binds to a protein called CD4 on T helper cells by its protein attachment site

RNA enters the cell

The reverse transcriptase converts the viral RNA into DNA

HIV DNA then creates mRNA which makes viral proteins

mRNA diffuses out of the nucleus and the cell now makes new HIV particles

Question 3

7 steps to the ELISA test

Answer 3

1. Add antigens to the well
2. Add patient serum e.g. blood
3. Allow antibody to bind to the complementary antigen
4. Wash removed unbound antibodies
5. Add a second antibody that is complementary to the first, but with enzyme attached
6. Wash again to remove unbound antibody
7. Add a substrate which is complementary to the active site of the enzyme which results in a colour change

Question 4

When does herd immunity arise and what is the benefit

Answer 4

Herd immunity arises when a sufficiently large proportion of the population has been vaccinated to make it difficult for a particular pathogen to spread within that population, it is the most effective way to protect people who do not respond to vaccines or can’t be given them

Question 5

3 reasons why vaccines do not eliminate diseases

Answer 5

1. Antigen variability so immunity is short lived e.g. influenza virus
2. Certain pathogens “hide” inside cells e.g. cholera bacterium burrows into mucus lining of intestinal wall
3. Vaccination fails to produce immunity in all individuals e.g. defective immune systems

Question 6

Antigenic drift

Answer 6

Small changes that mean the pathogen may no longer be recognised by the immune system

Question 7

Antigenic shift

Answer 7

More considerable changes e.g. can lead to a pathogen being able to infect a new (type of) host

Question 8

Why is the flu an example of antigenic variation

Answer 8

The flu is an antigenic mutation which leads to every exposure being like a primary response

Question 9

What is a self antigen

Answer 9

A recognised tag in the surface of cells that does not cause an immune response

Question 10

What is a non-self antigen

Answer 10

A foreign tag on the surface of cells that activates an immune response

Question 11

Examples of where non-self antigens are found

Answer 11

Viruses

Bacteria

Another persons cells e.g. transplanted cells, blood transfusions

Abnormal body cells e.g. cancer cells, toxins

Question 12

Phagocytosis

Answer 12

1. The phagocyte is attracted to the pathogen by chemical products of the pathogen, it moves towards the pathogen along a concentration gradient
2. The phagocyte has several receptors on its cell-surface membrane that attach to chemicals on the surface of the pathogen
3. Lysosomes within the pathogen migrate towards the phagosome formed by engulfing the bacterium
4. The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium
5. The hydrolysis products of the bacteria are absorbed by the phagocyte

Question 13

Humoral response (antigen presenting)

Answer 13

Complementary T cells bind to antigen

Releases cytokines that stimulate the rapid mitosis of B cells

B cells differentiate into plasma cells

Plasma cells secrete complementary antibodies to antigen

Question 14

Passive immunity

Answer 14

Immediate

Direct contact with antigen NOT necessary

Short-term

Question 15

Active immunity

Answer 15

Time-lag

Direct contact with antigen IS necessary

Long-term

Question 16

Structure of HIV

Answer 16

2 RNA & viral enzymes surrounded by capsid

Surrounded by viral envelope

Attachment proteins on surface

Question 17

Example of natural active immunity

Answer 17

Direct contact with pathogen

Question 18

Example of natural passive immunity

Answer 18

Antibodies through breastmilk

Question 19

Example of artificial active immunity

Answer 19

Vaccination

Question 20

Example of artificial passive immunity

Answer 20

Infection of antibodies

Question 21

Monoclonal antibodies

Answer 21

Mouse infected with antigen

WBC produce antibodies with complementary shape to antigen

Spleen cells are extracted which are the cells that produce the lymphocytes which secrete the antibodies

Fuse with cancer cell to produce hybridoma

Divide rapidly to produce the correct antibodies

Question 22

B lymphocytes

Answer 22

Mature in the Bone marrow

Associated with humoral immunity (antibodies present in body fluids e.g. blood plasma)

Antibodies are specific proteins called immunoglobulins

Antibodies are Y shaped molecules

Question 23

T lymphocytes

Answer 23

Mature in the Thymus gland

Associated with cell-mediated immunity (involving body cells)

Question 24

What are antibodies made up of

Answer 24

4 peptide chains

2 light & short

2 heavy & long

Form an antigen-antibody complex through the variable region (binding site) on the antibody

Question 25

T cells

Answer 25

Pathogen invades body cell or engulfed by phagocytes Phagocyte places antigens from pathogen on its cell surface membrane (becomes antigen presenting cell) Specific receptors on the cell surface of T-helper cells bind to the antigen Activation of other T-helper cells to divide by mitosis to form clones The activated cloned T-cell can stimulate phagocytes to engulf pathogens by phagocytosis The cloned T-helper cell can destroy infected cells by secreting a protein that causes cell lysis by creating holes in their cell surface membrane The activated cloned T-cell can develop into a memory cell (ready for secondary immune response)

Question 26

B cells

Answer 26

The surface antigens of an invading pathogen are taken up by a B cell The B cell processes the antigens and presents them on its surface in a process known as “antigen presentation” Helper T cells attach to the processed antigens on the B cell thereby activating the B cell that has the correct antibody on its surface The correct B cell divides by mitosis to form a clone of B cells This is called clonal selection The B cell clone forms plasma or memory cells Plasma cells secrete antibodies and attach to antigens on the surface of the pathogen surface, destroying them (primary immune response)

Question 27

How do cytotoxic T cells kill infected cells

Answer 27

Produce a protein that makes holes in the cell-surface membrane Cell membrane becomes freely permeable to all substances thus the cell dies

Question 28

How the antibody leads to the destruction of the antigen (bacterial)

Answer 28

They cause agglutination of the bacterial cells - makes it easier for phagocytes to locate Serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached

Question 29

Direct monoclonal antibody therapy in cancer

Answer 29

Monoclonal antibodies are produced that are specific to antigens on cancer cells Antibodies are given to patient and attach themselves to the receptors on their cancer cells Attach to the surface of cancer cells and block the chemical signals that stimulate rapid and uncontrollable division

Question 30

Monoclonal antibodies in pregnancy testing

Answer 30

Placenta produces hCG hormone Present in mothers urine Monoclonal antibodies present on the test strip of pregnancy test are linked to coloured particles If hCG is present, creates a hCG-antibody-colour complex which creates a coloured line

Question 31

Ethics of using vaccines

Answer 31

Vaccines have side effects that may sometimes cause long term harm In vaccine testing, to what extent should individuals be asked to accept risk in the interests of public health? How acceptable is animal testing?

Question 32

Why are antibiotics ineffective against viral diseases?

Answer 32

No metabolic mechanisms or cell structures for them to disrupt Viruses also have a protein coat rather than a murein cell wall and so do not have sites where antibiotics can work