How Can Tiny Molecules of DNA Become Millions?

Image of an early PCR machine

There is an excellent technique that allows a small sample of DNA to be replicated and turned into millions. This technique is called polymerase chain reaction (PCR) which is an excellent tool that has been widely used in many different fields such as, medicine, forensic science, and biotechnology. Before the invention of the PCR machine, many scientists had to suffer by manually moving the tubes between different temperature conditions water baths, which was time-consuming and increased the chance of error. The

development of automated thermal cyclers made the process much faster by now allowing the machine itself to switch temperatures between steps.

PCR COMPONENTS

Before the cycle begins, a PCR mixture must be created. This mixture contains several key components that play an important role in the cycle which include the following:

1. DNA Template: The sample that contains the target sequence that needs to be replicated.

2. Forward & Reverse Primers: Short pieces of DNA, designed to bind to specific regions on the template and define the boundaries of the sequence being copied.

3. Nucleotides (dNTPs): The building blocks for new DNA strands.

4. Taq DNA polymerase: Responsible for synthesizing the new DNA.

PCR CYCLE

Once the reaction mixture is prepared, the tubes are placed into a thermal cycler. The PCR process consists of three main steps that repeats in cycles. The first step is denaturation, which occurs at a high temperature (around 95°C). During this step, the double-stranded DNA separates into two single strands. The next step, annealing, the temperature is lowered (50–68°C) the primers bind to(anneal) to their complementary sequences on the single-stranded DNA template. The third step, elongation, takes place at around 72°C and during this phase, the Taq polymerase adds nucleotides to the primers, building new strands of DNA that are complementary to the original template.

These three steps are repeated for about 25–35 cycles. With each cycle, the amount of DNA doubles, leading to a huge increase in the number of copies of the target sequence. By the end of the process, millions of copies of a specific DNA segment can be produced from a very small initial sample. Imagine having to do this cycle by hand!

Thermal Cycle Machine (THIS COST OVER $5,000!)

PCR plays a crucial role in advancing scientific discovery and solving real-world cases, since even a tiny amount of DNA can be amplified so much that it becomes easy to analyze. This ability to rapidly generate millions of copies of a specific DNA sequence has made PCR an essential tool in fields such as medicine, forensics, and genetics. Overall, its speed, sensitivity, and reliability continue to make it one of the most important techniques in modern biology.