Which one of the following statements about molecular diagnosis is incorrect?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → ELISA is based on the principle of nucleic acid amplification.
Molecular diagnosis aims at finding a disease early. Conventional tests detect a pathogen only after it has multiplied and produced symptoms. Techniques such as recombinant DNA technology, PCR (polymerase chain reaction) and ELISA (enzyme linked immuno-sorbent assay) can detect it much earlier.
Option (1) Recombinant DNA technology, PCR and ELISA are some of the techniques that serve the purpose of early diagnosis. — A correct statement. Recombinant DNA technology, PCR and ELISA are the techniques the book names for early diagnosis.
Option (2) The presence of a pathogen is normally suspected only when the pathogen has produced a disease symptom. — A correct statement. A pathogen is normally suspected only after it has produced a disease symptom. This is the problem molecular diagnosis tries to solve.
Option (3) ELISA is based on the principle of nucleic acid amplification. — An incorrect statement. ELISA is based on the principle of antigen-antibody interaction. It detects the antigens of the pathogen or the antibodies made against it. Amplification of nucleic acid is the basis of PCR, not ELISA.
Option (4) By the time a disease symptom appears, the concentration of the pathogen is already very high in the body. — A correct statement. A pathogen has to multiply a great deal before it causes symptoms, so by then its concentration in the body is already very high. PCR can find it much earlier, while its concentration is still very low.
NCERT Extract:
Molecular Diagnosis – “… Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible. Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis. Presence of a pathogen (bacteria, viruses, etc.) is normally suspected only when the pathogen has produced a disease symptom. By this time the concentration of pathogen is already very high in the body. However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR.”
Molecular Diagnosis – “… ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.”