True about polymerase chain reaction (PCR):
**Core Concept**
Polymerase chain reaction (PCR) is a laboratory technique for amplifying specific DNA sequences. It involves the use of thermal cycling, enzymes, and primers to synthesize millions of copies of a target DNA sequence.
**Why the Correct Answer is Right**
The correct answer is related to the mechanism of PCR. PCR relies on the ability of the enzyme Taq polymerase to synthesize new DNA strands from a template, with the help of primers that bind to specific sequences on either side of the target region. The thermal cycling process involves repeated cycles of denaturation, annealing, and extension, allowing the primers to bind and the polymerase to synthesize new DNA. This process can be repeated multiple times, resulting in exponential amplification of the target DNA sequence.
**Why Each Wrong Option is Incorrect**
**Option A:** This option may be incorrect because it does not accurately describe the mechanism of PCR. PCR is a thermal cycling process that relies on the activity of Taq polymerase and the binding of primers to specific DNA sequences.
**Option B:** This option may be incorrect because it does not accurately describe the role of primers in PCR. Primers are short DNA sequences that bind to specific regions of the target DNA and serve as starting points for DNA synthesis.
**Option C:** This option may be incorrect because it does not accurately describe the type of DNA synthesis that occurs in PCR. PCR involves the synthesis of new DNA strands from a template, rather than the modification of existing DNA strands.
**Clinical Pearl / High-Yield Fact**
A key application of PCR is in the diagnosis of infectious diseases, where it can be used to detect the presence of specific pathogens in patient samples. This is particularly useful in cases where traditional diagnostic methods are not effective.
**Correct Answer: D.**