haya.Learning made clear
Molecular diagnosis: PCR, probes and ELISA sheet
3-mark answer frame

What is molecular diagnosis? Explain how PCR and ELISA help in the early detection of disease.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Give the need. Conventional serum and urine tests detect a pathogen only after it has multiplied and caused symptoms.
  2. 2 · Explain PCR. PCR amplifies very low amounts of pathogen nucleic acid, so HIV or gene mutations in suspected cancer can be found early.
  3. 3 · Explain probes. A radioactive probe hybridises to complementary DNA; a clone with a mutated gene does not show on autoradiography.
  4. 4 · Explain ELISA. ELISA uses antigen-antibody interaction to detect the pathogen's antigens or the antibodies made against it.
  5. 5 · Link to real life. RT-PCR and ELISA kits are used in Indian labs and blood banks.
  6. 6 · Close in one line. So molecular methods find disease before symptoms, when treatment works best.

Scoring tip: Say what each test detects: PCR finds nucleic acid, ELISA finds antigens or antibodies.