Describe the procedure for DNA amplification by polymerase chain reaction \((\mathrm{PCR}) .\)

DNA amplification is a cornerstone of modern biotechnology and the PCR (Polymerase Chain Reaction) is the technique primarily used for this purpose. This powerful method enables scientists and researchers to take a minute amount of DNA and amplify it into millions of copies. This is particularly useful for various applications including genetics, forensics, and medical diagnostics. The principle behind DNA amplification through PCR is to recreate the natural DNA replication process in a controlled laboratory setting. By repeating the cycle multiple times, the quantity of a specific DNA region can be exponentially increased to a level that can be easily analyzed or manipulated for further study.

Denaturation is the first step in the PCR process and involves heating the DNA to a high temperature, usually around 95°C. The heat is intense enough to break the hydrogen bonds between the base pairs that hold the DNA strands together. As a result, the double helix 'unzips', yielding two separate single DNA strands. This separation is crucial as it provides single-stranded templates for the next phase, allowing the primers to bind and initiate synthesis. Without complete denaturation, PCR efficiency would be greatly reduced, potentially resulting in incomplete or nonspecific DNA amplification.

Following denaturation, the next important phase is annealing. In annealing, the temperature is lowered to between 50-65°C to enable the primers to attach to their complementary base sequences on the single-stranded DNA templates. Primers are specifically designed short DNA sequences that are a crucial component in specifying the region of the DNA to be amplified. Their proper binding is essential for the specificity of the PCR process. The temperature and time of annealing are carefully controlled to ensure that the primers bind optimally, affecting both the yield and specificity of the amplified product.

Once the primers have annealed to the target sequences, the temperature is raised again, to around 72°C, which is the optimal temperature for the DNA polymerase enzyme to function. DNA polymerase is the workhorse of PCR; it reads along the DNA template and adds complementary nucleotides (dNTPs) at the 3' end of the primer, 'extending' the DNA strand. This process effectively builds a new strand of DNA, complementary to the original template strand. The careful orchestration of time and temperature during this stage is key for accurate and efficient synthesis of the target DNA segment.

The PCR process brings all of these steps together into a cycle that is repeated typically 25-35 times. Each cycle of denaturation, annealing, and extension effectively doubles the amount of target DNA, leading to exponential amplification over successive cycles. In the end, the PCR process concludes with a final hold at a lower temperature to ensure the stability and integrity of the final amplified DNA product. The versatility and robustness of PCR have made it an indispensable tool in many fields requiring DNA analysis, and its automation has allowed for high-throughput and accurate DNA amplification critical for advancements in scientific research.