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AS · Practice questions · Antibodies and monoclonal antibodies

Specific shape, specific job.

Six original Cambridge-style questions on antibody structure, the hybridoma method and monoclonal antibodies in diagnosis and treatment.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
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Link every part to a job.

01
Explain
[4 marks]

Relate the structure of an antibody molecule to its function.

  • Variable regions have a specific shape that is complementary to one antigen, so the antibody binds only that antigen. ✓
  • There are two antigen-binding sites, so one antibody can bind two antigens and cause agglutination. ✓
  • The hinge region gives flexibility, so the antibody can bind antigens different distances apart. ✓
  • Disulfide bonds hold the four polypeptide chains together; the constant region binds receptors on phagocytes (opsonisation). ✓
02
Recall
[3 marks]

Describe three ways in which antibodies help to destroy or disable pathogens.

  • Agglutination: antibodies clump pathogens together, so they cannot spread and are easier for phagocytes to engulf. ✓
  • Neutralisation: antibodies bind to toxins or to the attachment sites of viruses, so they cannot affect or enter host cells. ✓
  • Opsonisation: antibodies coat pathogens, marking them so phagocytes recognise and engulf them faster. ✓
03
Recall
[4 marks]

Outline the hybridoma method for producing monoclonal antibodies.

  • A mouse is injected with the antigen, and B-lymphocytes making the antibody are taken from its spleen. ✓
  • The B cells are fused with myeloma (cancer) cells to form hybridoma cells. ✓
  • Hybridomas are grown separately and screened to find those making the required antibody. ✓
  • The selected hybridoma is cloned and grown in culture; the identical (monoclonal) antibodies are collected and purified. ✓
04
Explain
[3 marks]

Explain how a pregnancy test strip uses monoclonal antibodies to detect the hormone hCG in urine.

  • Mobile monoclonal antibodies with a coloured marker bind to hCG in the urine. ✓
  • The hCG-antibody complex moves along the strip and binds to fixed antibodies at the test line, so a coloured line forms. ✓
  • Unbound labelled antibodies are trapped at the control line, which shows the test has worked. ✓
05
Explain
[3 marks]

Some breast cancer cells have large numbers of a particular receptor protein on their surface. Suggest how a monoclonal antibody could be used to treat this cancer.

  • A monoclonal antibody complementary to the receptor binds only to the cancer cells. ✓
  • It can block the receptor so growth signals cannot bind, slowing division of the cancer cells. ✓
  • It may also mark the cells for destruction by the immune system or carry an attached drug to them, so healthy cells are less affected. ✓
06
Analysis
[2 marks]

Monoclonal antibodies made in mice can cause an immune response when given to patients. Explain why, and suggest how this problem is reduced.

  • Mouse antibodies are proteins with non-self antigens, so the patient's immune system makes antibodies against them. ✓
  • Humanised antibodies are made, in which most of the molecule (except the binding sites) is human, so they are less likely to be recognised as non-self. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.