DNA Replication The Details

The enzyme Helicase breaks the hydrogen bonds holding parent strands together. This results in an unzipped helix that terminates at a replication fork.

Single Strand Binding proteins (SSB’s) bind to the newly exposed parent strands preventing them from reattaching.

DNA Polymerase III is the enzyme that brings in the free nucleotides to build the new complementary strands of DNA. However, it needs things called RNA primers to get it started. The enzyme Primase lays down these RNA primers.

DNA Polymerase III can build a new strand continuously in only one direction – in the 5’ to 3’ direction. This strand, called the Leading Strand, is built continuously toward the fork. The other strand, called the Lagging Strand, is built in short segments (Okazaki fragments) discontinuously away from the replication fork.

DNA Polymerase I cuts out the RNA primers and replaces them with the appropriate DNA nucleotides. DNA ligase joins the gaps in the Okazaki fragments. Polymerase I and Polymerase III proofread by removing incorrect nucleotides and replacing them with correct ones.

What do we mean by 5’ and 3’ ends of DNA? http://www.youtube.com/watch?v=p835L4HWH68

DNA Replication Song! (Study Aid!) http://www.youtube.com/watch?v=hyI2mYfbbxk