Question

Primers (forward and reverse) are synthetic oligonucleotides of 17-30 nucleotides. They are complementary to the sequence present on the desired DNA segment. Why?

Answer 1

Hint: The primers are an essential component required for the replication process of DNA. Primers are small segments of nucleotides that have complementary bases to the target stand to which they attach. It is known that two strands of DNA are attached to each other due to their complementarity. Primers also use the principle of complementarity.

Complete answer: Primers are short stretches of nucleotides ranging from 17-30 base pairs. These nucleotides have a sequence opposite to the strand of DNA to which they attach or bind. Primers are initiators for the replication process. Replication occurs to make copies of DNA and to form new DNA strands inside the nucleus. Replication occurs with the splitting of two strands of DNA. The double-stranded DNA splits into two individual strands making a replication fork. Each strand serves as a template for the formation of new DNA. For the synthesis of a new strand, an enzyme called DNA polymerase adds nucleotide bases complementary to the target strand which needs to be replicated. DNA polymerase needs a primer to initiate the extension process. Primer is the initiator molecule that binds to the starting point of DNA and then DNA polymerase adds nucleotides from the 3' end of the primer.

DNA polymerase adds bases only to existing sequences and thus primers are necessary for the replication process. Primers are also designed synthetically in PCR reactions. Every DNA sequence has a specific primer for it.

Note: In polymerase chain reaction each of the separated strands of DNA is supplied with start and end primers. These are called forward and reverse primers respectively. The DNA polymerase adds bases to these primers and initiates the extension of both primers towards each other. This results in copies of the target DNA.