What happens at 72 degrees in PCR?

Posted by Jack on December 13, 2022
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    When you're trying to grow a plant, one of the first things you do is isolate the DNA. You've probably seen how easy it is to extract DNA from strawberries or bananas by using a kitchen blender and some water. But this isn't the method used in labs; instead, they use a process called polymerase chain reaction (PCR) that allows them to make millions of copies of just one small piece of genetic material. PCR works by heating up specific DNA molecules so that they unzip and attach themselves back together when cooler again. Here are step-by-step instructions for what happens inside your microwave oven when you heat up your food:

    Denaturation of DNA at 95 degrees Celsius

    Denaturation of DNA at 95 degrees Celsius

    In order to make DNA susceptible to polymerase chain reaction, you must first denature it. Denaturation is the process of breaking the hydrogen bonds in DNA. This allows your DNA sample to be more accessible so that polymerases can bind and replicate your DNA strands.

    Annealing at 50 degrees Celsius

    Annealing is the process of hybridizing (to form a double-stranded DNA molecule) two complementary nucleic acids that have been denatured.

    In PCR, it is important to maintain the temperature between 50 and 60 degrees Celsius for at least 30 minutes. This ensures that the temperature does not get too high or too low. If you are using a thermocycler, which is a device that heats and cools samples automatically, this step is handled by the machine itself; however, if you're running your reaction in a glass tube on your stovetop (or something similar), it's important to monitor this carefully.

    Extension of primers at 72 degrees Celsius

    Extension of primers at 72 degrees Celsius

    The final step in the PCR process is called extension. During this step, DNA polymerase extends each primer by adding nucleotides to the 3’ end of each primer. This process only happens when the temperature reaches a certain level – 72 degrees Celsius (or about 162 degrees Fahrenheit) is optimal. However, it’s important to note that different people may have slightly different optimal temperatures for their specific PCR setup. If you find your results are varying from what you expect them to be, try adjusting your temperature setting!

    Polymerase chain reaction produces copies of a specific segment of DNA.

    PCR is a process that can be used to amplify a segment of DNA. The term "polymerase chain reaction" comes from the fact that it makes multiple copies of your DNA segment by adding new molecules onto the original template strand. In order to do this, there are four basic steps:

    • Denaturing: This step involves breaking apart (denaturing) the double-stranded DNA and turning it into single strands so they can be copied
    • Annealing: This step involves heating up your DNA so it cools down enough for new pieces of nucleotides (parts that make up DNA) to stick onto it. The temperature has to cool down enough so that when you add more nucleotides later on, they'll stick on, but not too cool where nothing sticks on at all!
    • Elongation: Once you've added these new pieces onto your tiny piece of DNA (which is now called an "oligonucleotide"), you need those olignucleotides to grow longer until they're long enough for further analysis or detection methods such as PCR itself!

    Denaturation: Double-stranded DNA (dsDNA) is heated to 94-95 degrees Celsius. This melts apart the two strands, creating two single-stranded DNA (ssDNA).

    The denaturation step is the first of three phases. It takes place at 94-95 degrees Celsius, which is hot enough to melt apart the two strands of dsDNA. This results in single-stranded DNA (ssDNA).

    Annealing: Primers bind to their complimentary sequence in the ssDNA.

    Annealing is the process by which primers bind to their complimentary sequence in the ssDNA. It takes place at temperatures above the melting point of DNA, usually between 60-65°C for most PCR reactions.

    Extension: The enzyme Taq polymerase uses each template DNA strand as a guide to make a complementary strand using dNTPs.

    Taq polymerase, an enzyme used in PCR, uses each template DNA strand as a guide to make a complementary strand using dNTPs.

    DNA is denatured, primed and extended at 98, 60 and 72 degrees Celsius respectively in PCR.

    To understand what happens at various temperatures, let's look at the three steps in PCR:

    • Denaturation is done at 94-95 degrees Celsius. This is to break up the DNA molecule into single strands so that it can be copied.
    • Primer annealing occurs when you lower the temperature to 60 degrees Celsius. A primer binds to your DNA strand and starts copying from there – like a book starting from chapter one and continuing until it reaches its end point, which is usually around 10kbp (kilobase pairs).
    • Extension occurs when you raise the temperature back up to 72 degrees Celsius for each cycle of PCR. This step requires an enzyme called Taq polymerase that makes copies of your newly created DNA strand until it reaches its end point – typically another 10kbp section


    As you can see, PCR produces copies of a specific segment of DNA. Through this process, it's possible to create millions of copies from just one original molecule. The polymerase chain reaction is an important tool for scientists who study genetics and work in forensic science fields like forensics or paternity testing. The ability to amplify small amounts of DNA means that doctors can use tests like these when diagnosing patients with diseases that may have genetic causes such as cancer or diabetes mellitus type II (also known as type 2 diabetes). If you'd like more information about how PCR works or how it might be used in your own research projects, check out our website at

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