Antibodies,vaccination,HIV

Question 1

What are antibodies

Answer 1

Antibodies are proteins with specific binding sites that are synthesised by B cells. They have a complementary shape to a specific antigen.

Question 2

Explain how antibodies bind to pathogens.

Answer 2

• When the body is infected with a non-self material, a B cell produces a specific antibody.
• This specific antibody reacts with an antigen on the surface of the non-self material by binding to them.
• Each antibody has two identical binding sites.
• The antibody binding sites are specific to a specific antigen.

Question 3

What six things does an antibody consist of

Answer 3

1) Two light chains
2) Two heavy chains
3) A variable region that is different in different antibodies
4) A constant region
5) Receptor binding site
6) Two identical antigen binding sites.

Question 4

Describe the structure of an antibody

Answer 4

• Antibodies have a quarternary structure (represented as a Y shape) with two heavy (long) polypeptide chains bonded by disulphide bridges and two light (short) polypeptide chains.
• Each polypeptide chain has a constant region and a variable region.
• The antibodies binding sites have a specific shape which is complementary to one antigen.
• They bind to form the antigen-antibody complex.

Question 5

Do antibodies destroy the pathogen

Answer 5

No, antibodies do not destroy antigens directly- they prepare the antigens for destruction.

Question 6

Describe two ways in which antibodies assist the destruction of the pathogen when the antigen is a bacterial cell

Answer 6

1) They cause the agglutination of bacterial cells. Clumps of bacterial cells are formed, making it easier for the phagocytes to locate them as they are less spread out within the body.
2) They serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached.

Question 7

Define monoclonal antibodies

Answer 7

The isolation and cloning of a single type of antibody.

Question 8

Describe how direct monoclonal antibody therapy can be used to treat cancer

Answer 8

• Monoclonal antibodies are produced that are specific to antigens on cancer cells.
• These antibodies are given to a patient and attach themselves to the receptors on their cancer cells.
• They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrolled growth.

Question 9

What is indirect monoclonal antibody therapy

Answer 9

When a radioactive or cytotoxic drug is attached to the monoclonal antibody so that when the antibody bonds to the cell/pathogen, the drugs kills them

Question 10

How do pregnancy tests work

Answer 10

• When someone is pregnant, the placenta produces the hormone HCG which is found in the urine of the mother.
• The monoclonal antibodies present on the test strip are linked to coloured particles.
• If HCG is present, it binds to these antibodies.
• The HCG-antibody-colour complex moves along the strip until it is trapped on other antibodies further up the strip where it creates a coloured line.

Question 11

Summarise the three key ethical issues in the use of monoclonal antibodies

Answer 11

1) Giving cancer to mice in order to produce them
2) Informed consent (risk vs benefits)
3) How drug trails are conducted

Question 12

Define immunity

Answer 12

The ability of an organism to resist infection

Question 13

What is passive immunity

Answer 13

Passive immunity is produced by the introduction of antibodies to an individual from an outside source. No contact with the pathogen or its antigen is needed to induce immunity. Immunity is acquired immediately. As the antibodies are not being produced by the individuals themselves, the antibodies are not replaced when they are broken down, no memory cells are formed and so there is no lasting immunity. (Eg anti-venom)

Question 14

What is active immunity

Answer 14

Active immunity is produced by stimulating the production of antibodies by the individuals own immune system. Direct contact with the pathogen or its antigen is necessary and immunity takes time to build up.

Question 15

What are the two types of active immunity

Answer 15

• Natural active immunity
• Artificial active immunity

Question 16

What is natural active immunity

Answer 16

Immunity that results from an individual becoming infected with a disease under normal circumstances.

Question 17

What is artificial active immunity

Answer 17

Artificial active immunity forms the basis of vaccination. It involves inducing an immune response in an individual without them getting the symptoms of the disease.

Question 18

List the factors that the success of a vaccination programme may depend on (what must a vaccine be)

Answer 18

• A vaccine must economically available in sufficient quantities
• Few side effects (an unpleasant ones discourage people from taking it)
• Means of producing,storing and transporting the vaccine must be available which usually involves technologically advanced equipment, hygienic conditions and refrigerated transport.
• There must be means of administering the vaccine properly at the appropriate time.
• It must be possible to vaccinate the vast majority of the vulnerable population to achieve herd immunity.

Question 19

What is herd immunity

Answer 19

Herd immunity is when a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within the population.

Question 20

List the reasons why vaccinations may not eliminate a disease

Answer 20

• vaccination fails to induce immunity in some individuals
• Individuals may develop the disease immediately after vaccination before their immunity levels are high enough to prevent it.
• The pathogens may mutate frequently, so that its antigens change suddenly rather than gradually. This means the vaccines will become ineffective.
• There may be so many varieties in a particular pathogen that a vaccine is not effective against them all.
• Individuals may have objections to vaccines for personal reasons.

Question 21

Describe the structure of the human immunodeficiency virus

Answer 21

• On the outside is a lipid envelope embedded in attachment proteins.
• Inside the envelope is a protein layer called a capsid that encloses two single stands of RNA and some enzymes.
• One of these enzymes is reverse transcriptase which can make DNA from RNA and therefore HIV is a retroviruses

Question 22

How does HIV replicate itself by using a host cell

Answer 22

1) Following infection HIV enters bloodstream and circulates around the body.
2) A protein on the HIV readily binds to a proteins called CD4. While this protein occurs on a number of different cells HIV most frequently attaches to T helper cells.
3) The protein capsid fuses with the cell-surface membrane. The RNA and enzymes of HIV enter the helper T cell.
4) The HIV reverse transcriptase converse the viruses RNA into DNA
5) The newly made DNA is moved into the helper T cells nucleus where it is inserted into the cells DNA.
6) The HIV DNA in the nucleus creates messenger RNA using the cells enzymes. The mRNA contains the instructions for making new viral proteins and the RNA to go into the new HIV
7) The mRNA passes out of the nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles.
8) The HIV particles break away from the helper T cell with a piece of its cell-surface membrane surrounding them which forms their lipid envelope.

Question 23

Describe how HIV causes the symptoms of AIDS

Answer 23

• HIV specifically targets helper T cells.
• Without a sufficient number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or the cytotoxic T cells that kill cells infected by pathogens.
• Memory cells may also become infected and be destroyed.
• As a result, the body is unable to produce an adequate immune response and becomes susceptible to other infections and cancers.

Question 24

What is the ELISA test used for

Answer 24

To detect the presence and quantity of a protein in a sample by using antibodies.

Question 25

Describe the procedure for carrying out an ELISA test

Answer 25

1) Apply the sample to a surface (eg a slide) to which all the antigens in the sample will attach.
2) Wash the surface several time to remove any unattached antigens.
3) Add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together.
4) Wash the surface to remove excess antibodies.
5) Add a second antibody that binds to the first antibody. This second antibody has an enzyme attached to it.
6) Add the colourless substrate of the enzyme. The enzyme acts on the substrate to convert it into a coloured product.
7) The amount of the antigen present is relative to the intensity of colour that develops.

Question 26

Why is the ELISA test useful for drug testing

Answer 26

Because it measures the quantity of the antigen present. Many drugs are found naturally at low levels in the body so the quantity present is key to drug testing.

Question 27

Why don’t antibiotics work on viral infections

Answer 27

• Viruses rely on the host cells to carry out their metabolic activities and therefore lack their own metabolic pathways and cell structures.
• As a result, there are 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.