DNA Review What does DNA store that is important? If a DNA strand read AGT-CCG-GTA what would the complimentary strand read? What holds the nitrogen bases together? What are the 3 components of a nucleotide?

DNA Replication DNA Replication- the process of making a copy of DNA Why is this important? – Cells need to copy their DNA for mitosis (growth, repair, and maintenance) Three steps: – Double helix unwinds and DNA helicase opens the strand – DNA polymerases add nucleotides back – Polymerases detach once replication is complete – You end with 2 stands of identical DNA strands

DNA Replication Step 1:  The double helix must unwind before replication can begin.  DNA helicases are enzymes that open the double helix by breaking the hydrogen bonds that hold the complimentary bases together (think of a zipper)  Replication goes from 5’ to 3’

DNA Replication Step 1 con’t:  Once separated, additional proteins hold the strands apart.  Where the double helix separates is called a replication fork (because of it’s Y shape)

DNA Replication Step 2:  At the replication fork enzymes called DNA polymerases move along each of the DNA strands.  DNA polymerases add nucleotides to the exposed bases according to the base pair rules

DNA Replication Step 3:  Step 2 continues until all DNA has been copied and the polymerases detach  Produces 2 DNA molecules that are identical to each other and the original strand