Quick Review Cards for Medical Laboratory Science

Primer Extension

Molecular Diagnostics

(MDx) Review 536

Template DNA: 3’ AGCA 5’

Æ (DNA polymerase reads template, attaches nucleotides in this direction

Daughter strand: 5’ TCGT 3’

Polymerase reads template in 3’ to 5’ direction. New strand grows in 5’ to 3’ direction

In example above:

1. Polymerase reads A on template, adds T to daughter strand


2. Polymerase reads G on template, adds C to daughter strand


3. Polymerase reads C on template, adds G to daughter strand


4. Polymerase reads A on template, adds T to daughter strand

5’ P of incoming nucleotide attaches to 3’ OH of last nucleotide on strand, forming phosphodiester bond