Antibodies

Question 1

What are antibodies?

Answer 1

large Y-shaped protein molecules that can recognise and neutralise antigens and are produced by B lymphocytes (plasma B cells)

Question 2

What is the structure of antibodies?

Answer 2

• Made up of 4 polypeptide chains - 2 heavy and 2 light.
• Each has a specific binding site complementary to the antigen. • They bind to the antigens on the surface of the pathogen to form antigen- antibody complexes. • Each binding site consists of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen. The rest is the constant region this is the same for all antibodies
• polypeptide chains held together by disulfide bridge

Question 3

What are the 3 ways antibodies combat pathogens?

Answer 3

1. Agglutination - forming antibody-antigen complexes, the pathogens are held together in large clumps. Macrophages and neutrophils can more easily engulf pathogens which are immobilised by agglutination. Agglutination is possible because each antibody has two antigen binding sites
2. Neutralisation - antigens which are toxins are rendered harmless if they are blocked by being bound to an antibody
3. Act as markers that attract the phagocytes - the phagocytes will then engulf the microorganism/pathogen

Question 4

What are monoclonal antibodies?

Answer 4

Antibodies produced from a single group of genetically identical plasma B cells

Question 5

What are anti cancer drugs?

Answer 5

Drugs targeted towards cancer cells. Cancer cells have antigens called tumour markers on their surface that are not sound on normal body cells. Monoclonal antibodies can be produced that will bind to the tumour marker. You can attach anti cancer drugs to antibodies. This means the drugs will only accumulate in the body where there a cancer cells so the side effects are less

Monoclonal antibodies used this way are called “magic bullets” and can be used in smaller doses making it cheaper as well as reducing possible side effects

Question 6

What are the ethical issues of monoclonal antibodies?

Answer 6

• production is them incomes the use of mice. Mice used to product antibodies and tumour cells are deliberately induced to have cancerous cells
• monoclonal antibodies have been used successfully to treat diseases, however there has been some deaths associated with their use in the treatment of multiple sclerosis

Question 7

How are monoclonal antibodies used in pregnancy testing?

Answer 7

• when a human embryo implants into the uterine lining it secretes a hormone called hCG. hCG can be found in human urine 6 days after conception
• pregnancy tests contain monoclonal antibodies specific to hCG which acts as the antigen
• if urine contains hCG then it will attach to antibody which is tagged with a blue bead
• this hCG-antibody complex will move up the pregnancy test strip until it sticks to a band of immobilised antibodies where they will accumulate and form a blue line
• the strip also contains one control blue line that will show that any antibody- complexes which haven’t bound to any hCG have moved up to strip to use as a comparison and show that is it working

Question 8

What is the ELISA test?

Answer 8

Allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody

It can be used in medical diagnosis to test for pathogenic infections and allergies

Question 9

Describe the role of antibodies in producing a positive result in an ELISA test

Answer 9

• antibody binds to antigen
• add antibody with enzyme attached
• antibody attaches to antigen
• bringing of the active site to substrate causes a colour change showing a positive result

Question 10

What is the method for the Direct ELISA test?

Answer 10

Uses one antibody that is complementary to the antigen

1. Collect a sample form a patient - this contains the antigen
2. Add antibody with enzyme attached
3. If antigen present antibody binds
4. Wash to remove any unbound antibodies
5. Add substrate
   complementary to enzymes active
   site
6. Coloured product formed if antigen present

Question 11

What is the method for the Indirect ELISA test?

Answer 11

Using two different antibodies

1. Antigen bounded to bottom of well, complementary to the antibody being tested for
2. Sample of patients blood plasma added. Any antibodies specific to antigen will bind to the antigen
3. Wash to remove any unbound antibodies
4. A second antibody is added that has enzyme attached. This will bind to the HIV (1st) antibody
5. Wash to remove any 2nd antibodies that have not bound
6. Substrate added and any colour change will indicate a positive result ie antibodies are present in sample