Monoclonal antibodies and ELISAAQA A-Level Biology: Subtopic test

1. 1
   A hospital is trialling a treatment for a type of breast cancer. A cancer drug is attached to a monoclonal antibody. The antibody binds to a receptor protein that is present in very large numbers on the surface of the tumour cells and in very small numbers on healthy cells.

   (a)

   Which statement describes monoclonal antibodies?

   [1 mark]

   • AThey are different antibodies made by many different plasma cell clones, each binding a different antigen
   • BThey are identical antibodies made by a single clone of plasma cells, all binding the same antigen
   • CThey are antigens that stimulate the production of memory cells
   • DThey are enzymes that hydrolyse the antigens on cancer cells

   (b)

   Why does attaching the drug to the antibody reduce the side effects of the treatment?

   [1 mark]

   • AThe antibody destroys the healthy cells so that the drug is not needed there
   • BThe antibody makes the drug less toxic to every cell in the body
   • CThe antibody stops the drug being broken down by enzymes in the blood
   • DThe antibody carries the drug to the tumour cells, so little drug reaches healthy cells

   (c)

   Explain why the antibody binds to the tumour cells but not to most healthy cells.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A diagnostic laboratory uses an ELISA test to detect a viral antigen in blood samples. The wells of a plastic plate are coated with the patient's sample so that any antigen sticks to the plastic. A first antibody specific to the viral antigen is then added, followed by a second antibody that carries an enzyme and binds to the first antibody. A colourless substrate is added last.

   (a)

   Why are the wells washed after the first antibody has been added?

   [1 mark]

   • ATo remove any unbound first antibody so that it cannot be bound by the second antibody
   • BTo destroy the antigen that is not needed for the test
   • CTo activate the enzyme attached to the second antibody
   • DTo make the substrate colourless

   (b)

   What is the function of the enzyme attached to the second antibody?

   [1 mark]

   • AIt binds to the viral antigen directly
   • BIt destroys the first antibody once the test is complete
   • CIt converts the colourless substrate into a coloured product
   • DIt makes the second antibody bind to plastic

   (c)

   A technician forgets to wash the well after adding the second antibody. Explain the effect on the result for a well that contains no viral antigen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A home pregnancy test detects the hormone hCG in urine. The urine is applied to a pad that contains mobile monoclonal antibodies to hCG attached to blue beads. The liquid flows along a strip past a test line of immobilised monoclonal antibodies to hCG, and then past a control line of immobilised antibodies that bind the mobile antibodies.

   (a)

   Explain how a blue test line appears when the urine contains hCG.

   [3 marks]

   (b)

   The manufacturer uses monoclonal antibodies rather than a mixture of different antibodies from blood serum. Explain how this reduces the chance of a false positive result.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pharmaceutical company has developed a monoclonal antibody–drug conjugate for a form of cancer. In a clinical trial, 600 patients were randomly allocated to two equal groups. One group received the antibody–drug conjugate and the other received conventional chemotherapy. Median survival was 21.4 months with the conjugate and 17.9 months with chemotherapy. Severe side effects occurred in 14% of patients given the conjugate and 38% of patients given chemotherapy. All patients were aged 40 to 65, the trial lasted three years and it was paid for by the company that makes the conjugate.

   (a)

   Discuss the ethical issues associated with the use of monoclonal antibodies in medicine.

   [6 marks]

   (b)

   Evaluate the methodology and the data from the trial as evidence that the conjugate is better than conventional chemotherapy.

   [6 marks]

   Total for question 4: 12 marks

End of questions