Why Does a PCR Reaction Require a Primer?

Why does a PCR reaction require a primer? Would you expect this primer to be composed of DNA or RNA?

A) Primers provide energy B) Primers initiate DNA synthesis C) Primers stabilize RNA D) Primers degrade DNA

Final Answer:

Primers are required in PCR to initiate DNA synthesis because DNA polymerases cannot start from scratch.

Explanation:

A PCR reaction requires a primer for a very specific reason. Primers are necessary to initiate DNA synthesis because DNA polymerases, the enzymes that replicate DNA, are unable to start the synthesis of a new DNA strand from scratch. A primer provides a starting point with a free 3'-hydroxyl (3'-OH) group to which the DNA polymerase can add nucleotides.

In the context of PCR and DNA replication in living organisms, the primers are generally composed of RNA. RNA primers are synthesized by the enzyme primase, and they are later replaced by DNA. However, in PCR, DNA primers are used instead. DNA primers are chemically stable and can be specifically designed to bind to a particular segment of the target DNA, ensuring the amplification of the correct region.

In summary, primers initiate DNA synthesis, they are composed of DNA in PCR, which contrasts with the RNA primers that are synthesized by primase during cellular DNA replication. The correct answer to the multiple-choice question provided would be B - Primers initiate DNA synthesis.