DNA Replication Created by Kim Useglia-former student teacher Ask why, when, and where they think replication occurs? Ask them to recall when copies are needed? DNA Replication Created by Kim Useglia-former student teacher

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

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

Enzymes 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

Mutations

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

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

More practice 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

Review 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? DNA replication occurs during the S or synthesis phase of cells, during mitosis and meiosis, in the nucleus A and T are complimentary base pairs Helicase, breaks hydrogen bonds and DNA polymerase, adds nucleotides and proofreads DNA

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

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

Procedure 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

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