Question

What is annealing?

Answer 1

Hint: The polymerase chain reaction (PCR) is a laboratory (in vitro) technique for generating large quantities of a specified DNA.

Complete step by step answer:
PCR is a cell-free amplification technique for synthesizing multiple identical copies (billions) of any DNA of interest. The double-stranded DNA of interest is denatured to separate into two individual strands. Each strand is then allowed to hybridize (form bonds with complementary nucleotides) with a primer (renaturation). The primer-template duplex is used for DNA synthesis (the enzyme DNA polymerase). These three steps— denaturation, renaturation/annealing, and synthesis are repeated again and again to generate multiple forms of target DNA. The actual technique of PCR involves repeated cycles for amplification of target DNA. Each cycle has three stages.
1. Denaturation: On raising the temperature to about 95°C for about one minute, the DNA gets denatured and the two strands separate.
2. Renaturation or annealing: As the temperature of the mixture is slowly cooled to about 55°C, the primers base pair with the complementary regions flanking target DNA strands. This process is called renaturation or annealing. A high concentration of primer ensures annealing between each DNA strand and the primer rather than the two strands of DNA.
3. Synthesis: The initiation of DNA synthesis occurs at the 3’-hydroxyl end of each primer. The primers are extended by joining the bases complementary to DNA strands.

Note: Applications of PCR:
The specificity and sensitivity of PCR are highly useful for the diagnosis of various diseases in humans. These include the diagnosis of inherited disorders (genetic diseases), viral diseases, bacterial diseases, etc.
PCR is very important in the study of evolutionary biology, more specifically referred to as phylogenetics. It is a technique which can amplify even minute quantities of DNA from any source (hair, mummified tissues, bone, or any fossilized material), PCR has revolutionized the studies in paleontology and archaeology.
Used in DNA fingerprinting too.