Question

Summarize the process of DNA replication

Answer 1

DNA replication occurs depends upon whether the cells is a prokaryote or a eukaryote (see the RNA sidebar on the previous page for more about the types of cells). DNA replication occurs in the cytoplasm of prokaryotes and in the nucleus of eukaryotes. Regardless of where DNA replication occurs, the basic process is the same.

The structure of DNA lends itself easily to DNA replication. Each side of the double helix runs in opposite (anti-parallel) directions. The beauty of this structure is that it can unzip down the middle and each side can serve as a pattern or template for the other side (called semi-conservative replication). However, DNA does not unzip entirely. It unzips in a small area called a replication fork, which then moves down the entire length of the molecule.
An enzyme called DNA gyrase makes a nick in the double helix and each side separates
An enzyme called helicase unwinds the double-stranded DNA
Several small proteins called single strand binding proteins (SSB) temporarily bind to each side and keep them separated
An enzyme complex called DNA polymerase "walks" down the DNA strands and adds new nucleotides to each strand. The nucleotides pair with the complementary nucleotides on the existing stand (A with T, G with C).
A subunit of the DNA polymerase proofreads the new DNA
An enzyme called DNA ligase seals up the fragments into one long continuous strand
The new copies automatically wind up again