Primer

Definition

A primer is a short strand of RNA or DNA that serves as a starting point for DNA synthesis. Primers are required because the enzymes that catalyze this process, like DNA polymerases, can only add new nucleotides to an existing strand of DNA.

5 Must Know Facts For Your Next Test

1. Primers are typically 18-22 nucleotides long.
2. In DNA replication, primers are synthesized by the enzyme primase.
3. Primers provide a free 3'-OH group for the addition of nucleotide triphosphates.
4. During polymerase chain reaction (PCR), synthetic primers are used to amplify specific segments of DNA.
5. Primers must be complementary to the target region in order to anneal properly during replication.

Review Questions

• What role does a primer play in DNA replication?
• Which enzyme is responsible for synthesizing RNA primers during DNA replication?
• Why can't DNA polymerases initiate the synthesis of a new DNA strand without a primer?

Related terms

DNA Polymerase: An enzyme that synthesizes new strands of DNA by adding nucleotides to an existing chain.

Primase:

An enzyme that synthesizes short RNA primers needed for DNA replication.

PCR (Polymerase Chain Reaction): A laboratory technique used to amplify specific segments of DNA using synthetic primers.