Cell Recognition & the Immune System

Question 1

Pathogen def + eg

Answer 1

A disease causing microorganism e.g. bacteria, virus, fungi, parasite

Question 2

Infection def

Answer 2

The interaction between a pathogen and the body’s defence mechanisms (an invasion of pathogens in the body)

Question 3

Immunity def

Answer 3

The means by which he body protects itself from infection

Question 4

Antigen def + eg

Answer 4

(Antibody generator) a foreign protein on the surface of pathogens or other non-self cells that causes an immune response by lymphocytes e.g. bacteria, viruses, fungi, parasites, cancerous abnormal body cells, toxins, transplanted cells

Question 5

Clonal selection def

Answer 5

When an antigen binds to the cell of a specific T cell clone or when a lymphocyte recognises a foreign molecule and is stimulated to divide

Question 6

Clonal expansion def

Answer 6

When a T cell clone has the ability to generate into many different cells

Question 7

Antibody structure

Answer 7

Light chains, heavy chains, hinge region, two antigen binding sites at the ends, variable regions, constant regions

Question 8

How do antibodies demonstrate the different protein structures?

Answer 8

Tertiary - disulfide bridge

Quaternary - made of more than one (four) polypeptide chains

Question 9

Passive immunity

Answer 9

Produced by the introduction of antibodies. No direct contact with a pathogen is necessary (eg anti-venom). Immunity is acquired immediately. Antibodies are not produced by the individuals themselves - immunity acquired by by the foetus from the mother when antibodies pass across the placenta to the womb. Antibodies are not replaced when they are broken down, no memory cells are formed, no lasting immunity

Question 10

Active immunity

Answer 10

Produced by stimulating the production of antibodies by the individual’s own immune system. Direct contact with the pathogen is necessary. Takes time to develop, but generally long lasting. Two types: natural or artificial

Question 11

Natural active immunity

Answer 11

Individual is infected under normal circumstances

Question 12

Artificial active immunity

Answer 12

Vaccinations immunisation programme). Induces an immune response without them suffering the symptoms

Question 13

Vaccination def

Answer 13

Small doses of dead or inactive pathogens or its antigens injected or taken by mouth to induce an immune response and produce memory cells without experiencing symptoms of the disease

Question 14

Features if a successful vaccination programme

Answer 14

Must be economically available in sufficient quantities to most vulnerable population. Must be few side-effects. Must have available means of producing, storing and transporting the vaccine (technologically advanced equipment, refrigerated transport, hygienic conditions). Must be means of administering the vaccine properly at the appropriate time. Produces herd immunity

Question 15

Why might vaccinations not eliminate a disease?

Answer 15

People have defective immune systems. Antigen variability (antigen change frequently so antibodies produced no longer match). Too many varieties of a pathogen. Some pathogens hide from the immune system (viruses in the lysogenjc cycle). Individuals object due to ethical, medical or religious reasons.

Question 16

How are monoclonal antibodies produced?

Answer 16

Mouse is vaccinated to produce antibodies. Antibody-forming cells taken from spleen. Tumour cells grown in tissue culture. Form hybridomas by fusing antibody-forming cells with cultivated tumour cells to stimulate growth. Hybridomas screened for antibody production. Cloned. Monoclonal antibodies isolated for cultivation

Question 17

Uses of monoclonal antibodies

Answer 17

Pregnancy testing, targeting medication, indirect monoclonal antibody therapy, medical diagnosis

Question 18

How does phagocytosis lead to presentation of the virus’ antigens?

Answer 18

The vesicle (phagosome) fuses with a lysosome. The virus is hydrolysed by lysozymes. The broken down antigen are then presented on the cell-surface membrane

Question 19

Why do antibodies only attack certain cells/antigens?

Answer 19

Antibodies have specific tertiary structures. The binding sites and variable regions are complementary to the antigen. The antigen is found on specific cells. Therefore the antibody only binds with these cells

Question 20

Why can’t ELIZA tests be used to find out if a person has AIDS?

Answer 20

The ELIZA test only shows the number of helper T cells. A person can be HIV-positive but not have AIDS as it doesn’t show the symptoms of the patient

Question 21

In an ELIZA test what are the reasons for having a control well?

Answer 21

To show the enzyme is causing a colour change. To show that the washing is effective.

Question 22

If a HIV positive mother gives birth to a baby, explain why the positive result does not prove that they are infected?

Answer 22

Passive immunity would’ve taken place so the solution would have turned blue

Question 23

How do vaccines lead to the production of antibodies?

Answer 23

A macrophage present antigens on its surface. T cells with complementary receptor proteins binds to the antigen. This stimulates B cells. The B cell divides to form clones or secrete antibodies or presents antibodies on the cell surface membrane

Question 24

How is HIV replicated after into the human cell?

Answer 24

HIV joins to the host DNA. Reverse transcriptase turns the viral RNA to DNA. HIV proteins are therefore copied in protein synthesis. This is made at ribosomes.

Question 25

How does the destruction of T cells by HIV lead to death?

Answer 25

There are not enough T cells to activate B cells. The person will be unable to fight infections such as TB

Question 26

Structure of HIV

Answer 26

Lips envelope on the outside, attachment proteins embedded in, capsid protein layer inside the envelope, encloses two single strands of RNA and enzymes eg reverse transcriptase, matrix

Question 27

Reverse transcriptase function

Answer 27

Catalyses the production of DNA from RNA

Question 28

Retroviruses def

Answer 28

Contain reverse transcriptase and have the ability to make DNA from RNA

Question 29

How does HIV replicate it self?

Answer 29

HIV enters the bloodstream and circulates around the body. A protein on HIV readily binds to a protein called CD4. This protein occurs on a number of different cells but HIV most frequently attaches to helper T cells. The protein capsid fuses with the cell-surface membrane. The RNA and enzymes of HIV enter the T-cell. HIV reverse transcriptase converts the viruses RNA into DNA. The newly made DNA is moved to the helper T cell’s nucleus where it is inserted into the host cells DNA. Here it creates mRNA which contains the instructions for making new viral proteins and the RNA to go into new HIV. The mRNA passes out of the nucleus through nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles. These break away from the helper T-cell with a piece of its cell-surface membrane to form a lipid envelope.

Question 30

How does HIV cause symptoms of AIDS?

Answer 30

It’s a tax helper T cells by killing or interfering with the normal functioning of them. Without a sufficient number of helper T cells, the immune system can’t stimulate B cells to produce antibodies or cytotoxic T cells that kill cells infected by pathogens. Memory cells can also be infected and destroyed. This means that the body is unable to produce an adequate immune response and becomes susceptible to other infections and cancers. These secondary diseases caused death