Biology · Biotechnology and Its Applications · NEET
Conventional methods usually detect a pathogen only after it has already produced disease symptoms. By that time the concentration of the pathogen in the body is already very high. So early detection is not possible with these methods. Molecular methods can catch the pathogen much earlier, when its amount is still very low.
PCR amplifies (makes many copies of) the nucleic acid of the pathogen. Even if only a very low amount of the pathogen's DNA/RNA is present, PCR multiplies it to a detectable level. This lets doctors find the pathogen before symptoms appear. NCERT states PCR is routinely used to detect HIV in suspected AIDS patients and to detect gene mutations in suspected cancer patients.
NCERT lists three: (1) Recombinant DNA technology, (2) Polymerase Chain Reaction (PCR), and (3) Enzyme Linked Immuno-Sorbent Assay (ELISA). Remember these three by name for NEET, because the exam often asks which technique does NOT serve early diagnosis.
A single-stranded DNA or RNA tagged with a radioactive molecule is called a probe. It is made complementary to a normal gene. It hybridises (base-pairs) with its matching sequence in a clone of cells, and the position is found by autoradiography. If a gene is mutated, the probe cannot base-pair with it, so that spot does not appear on the photographic film. Absence of signal reveals the mutation.
ELISA is based on antigen-antibody interaction. It detects the presence of antigens (parts of the pathogen) or antibodies made against the pathogen. Because it can find these markers early, ELISA is used for early detection of infection, and NCERT notes it is a widely used diagnostic test for AIDS.
Which one of the following techniques does not serve the purpose of early diagnosis of a disease for its early treatment?
For effective treatment of the disease, early diagnosis and understanding its pathophysiology is very important. Which of the following molecular diagnostic techniques is very useful for early detection?
Now a days it is possible to detect the mutated gene causing cancer by allowing radioactive probe to hybridise its complementary DNA in a clone of cells, followed by its detection using autoradiography because:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is finding a disease very early, before symptoms show, by detecting the pathogen even when its amount in the body is still very low, using techniques like PCR, ELISA and recombinant DNA technology.
For effective treatment, early diagnosis and understanding the pathophysiology of a disease are very important. Catching a pathogen early, when its concentration is low, allows treatment to start before serious damage occurs.
ELISA is based on antigen-antibody interaction (immunology), not on amplifying DNA. It is still counted as a molecular diagnostic technique for early detection and is widely used to test for AIDS.
A probe is a single-stranded DNA or RNA tagged with a radioactive molecule. It hybridises with its complementary sequence, and its position is detected by autoradiography, which helps locate or check a specific gene.
