Understanding Polymerase Chain Reaction (PCR) in Molecular Biology: A Step-by-Step Guide

polymerase chain reaction

genetic engineering technique that can make copies of specific regions of a DNA fragment

Polymerase chain reaction (PCR) is a technique in molecular biology used to amplify a specific segment of DNA. The process involves three main steps: denaturation, annealing, and extension.

In the denaturation step, the DNA sample is heated to a high temperature (usually around 95°C) to break the hydrogen bonds between the two strands and separate them.

In the annealing step, the temperature is lowered to allow short, single-stranded primers to anneal or bind to the target DNA sequence on each strand. These primers are synthesized to match the ends of the target DNA sequence and act as starting points for the polymerase to extend from.

In the extension step, a DNA polymerase (usually Taq polymerase) is activated and synthesizes a new complementary strand of DNA starting from the primers. The polymerase reads the template strand 3′ to 5′ and adds complementary nucleotides in the 5′ to 3′ direction, thereby extending the primers and amplifying the target DNA sequence.

The result of one PCR cycle is two double-stranded DNA molecules containing the target DNA sequence. Multiple cycles of denaturation, annealing, and extension can be performed in a thermal cycler machine to exponentially increase the amount of target DNA.

PCR is a powerful and widely used technique in molecular biology, with applications including DNA sequencing, genetic testing, forensic analysis, and disease diagnosis.

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