Question

In polymerase chain reaction, what is a primer and how can we change the primers to change the target sequence? I thought in PCR the DNA was just copied. I'm having trouble understanding that a specific sequence can be copied. I cant find videos to show me this process as I am really interested to see how this works. Please help me understand this part. Thank you.

Answer 1

A primer refers to a short fragment of single stranded DNA usually 15-30 nucleotide in length which are complementary to desired or target sequence. A PCR reaction cannot take place without a primer as their role is to provide free 3'OH group so that polymerase can add dNTPs to amplify the target sequence.

As we know that pcr is a very sensitive and specific tool. So if we change the sequence of the primer we are using it will change the target sequence as well because now the new primer will hybridize to its complementary template sequence which would be different from the earlier target.

The PCR refers to in vitro DNA replication and amplification. The polymerase enzyme can only add nucleotides to the end of an existing strand of DNA which is overcome by addition of a primer for the initiation of replication. These primers are specific to a target sequence and only hybridize to the complementary template sequence. Henceforth the amplification of the DNA template is controlled and is amplification of the target sequence only take place.

in this figure the former sequence which shows a grey arrow is being amplified as the primer used is complementary to the template sequence while the 2nd sequence isn't complementary to the primer and hence will not be replicated as the primer wouldn't hybridize with this template.