 DNA replicates before a cell divides  Occurs during the S or synthesis phase of the cell cycle  Replication creates identical copies of DNA strands  Takes place in the nucleus

DNA DOUBLE HELIX 3 Nitrogenous Base (A,T,G or C) “Rungs of ladder” “Legs of ladder” Phosphate & Sugar Backbone

 Begins at Origin of Replication  Two strands open forming a Replication Forks (Y-shaped region)  New strands grow at the forks ReplicationFork Parental DNA Molecule 3’ 5’ 3’ 5’

 The Enzyme, Helicase, unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds  DNA polymerase adds nucleotides complimentary to the parental strand

- Replication occurs at multiple sites along the DNA - DNA polymerase is very accurate - However mutations do occur - Proofreading occurs continuously by DNA polymerase

Write the complimentary strand: T A C G G A C T A A C G C

Write the complimentary strand: T A C G G A C T A A C G C A T G C C T G A T T G C G

 When and where does DNA replication occur?  What is the relationship between adenine and thymine called?  What are the two enzymes involved in DNA replication?

 In pairs you are going to create your own DNA models.

 Sugar - Black pentagon  Phosphate - White tube  Nitrogenous bases -  Adenine - Orange (5)  Guanine - Yellow (4)  Cytosine - Blue (4)  Thymine - Green (5)  Hydrogen bonds - White rods

 Create 18 nucleotides  Put together a 9 rung ladder of DNA  Be sure to have correct base pairing  After having a complete DNA molecule create 18 more nucleotides

 Begin to “unzip” DNA molecule from one end  Add complimentary nucleotides to create two DNA molecules