Seneca
Sign up

Antibodies

Biology: AQA A Level, topic 2.4.5

Structure

Antibodies are proteins called immunoglobulins that are produced by the plasma cells during the immune response. The antibodies are called monoclonal antibodies.

Variable regions

Variable regions

  • Each antibody has two variable regions.
  • Each antibody has different variable regions.
  • The variable regions bind specifically to specific antigens.
  • One antibody can bind two antigens. This allows the antigens to be clumped together in agglutination.
Constant regions

Constant regions

  • Every antibody has the same constant regions.
Disulphide bridge

Disulphide bridge

  • Antibodies are made from two heavy chains and two light chains.
  • The heavy chains are connected to the light chains by disulphide bridges.
Hinge protein

Hinge protein

  • The hinge protein connects the variable region to the constant region.

Uses of Monoclonal Antibodies

Monoclonal antibodies can be used in the following ways:

Targeted medication

Targeted medication

  • Cancer cells in the body have antigens that signal the cells as abnormal.
  • Monoclonal antibodies in cancer treatment can be used to bind specifically to the antigens on cancer cells.
  • Cancer treatments can be harmful to many cells. By binding specifically to cancer cells, the antibodies allow the treatment to be targeted to only the cancer cells.
  • This reduces damage to other cells.
Medical diagnosis

Medical diagnosis

  • Monoclonal antibodies can be used to indicate the presence of a specific antigen.
  • The antibodies are attached to a dye, fluorescent or radioactive marker.
  • When the complementary antigen is present, it will bind the antibody and the marker will become visible.
  • Monoclonal antibodies are used in this way in pregnancy tests.

ELISA Test

Antibodies can be used in the enzyme-linked immunosorbent assay (ELISA) test. ELISA test tests for infections (e.g. HIV) or allergies. The steps involved are:

1) Fixing of the antigens

1) Fixing of the antigens

  • The antigen for the infection that is being tested for is immobilised to the bottom of a beaker.
2) Addition of the blood

2) Addition of the blood

  • A sample of the blood that is being investigated is added to the beaker.
  • If the antibodies that are complementary to the disease-causing antigen are present in the blood, they will bind to the antigens at the bottom of the beaker to form many antigen-antibody complexes.
3) Washing of the beaker

3) Washing of the beaker

  • The beaker is washed out so that any antibodies that have not bound to antigens are removed.
4) Secondary antibodies

4) Secondary antibodies

  • Secondary antibodies are added to the solution.
  • The secondary antibodies are bound to an enzyme.
  • If a secondary antibody binds to the other antibodies from the blood sample, the enzyme will change the colour of a solution in the beaker.
5) Addition of the solution

5) Addition of the solution

  • The solution that reacts with the enzymes on the secondary antibodies is added.
  • If the solution changes colour, the secondary antibodies have bound to the antibodies from the blood sample.
  • This indicates the blood sample is infected by the pathogen.

Test yourself on Antibodies

  • Which of the following statements about antibodies are true?

  • What structure of the antibody binds to specific antigens?

  • Which of these is NOT a use of monoclonal antibodies?

  • Which of the following statements about uses of antibodies are true?

  • Which of the following statements of the ELISA test are true?

Practise this topic for free