1. DNA Replication Section 12.2

2. Why and When? DNA needs to be copied in preparation for mitosis/meiosis. Occurs during “s” phase of the cell cycle.

3. DNA Replication DNA Replication Origins of replicationOrigins of replication Replication ForkshundredsY-shaped replicating DNA molecules Replication Forks: hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing. ReplicationFork Parental DNA Molecule 3’ 5’ 3’ 5’

4. DNA Replication DNA Replication Origins of replicationOrigins of replication Replication Bubbles Replication Bubbles: Hundreds (Eukaryotes) a.Hundreds of replicating bubbles (Eukaryotes). Single(bacteria). b.Single replication fork (bacteria). Bubbles

5. DNA Replication DNA Replication 4 Steps:4 Steps: 1.Unwinding 2.Priming 3.Synthesis of the New DNA Strand 4.Joining

6. DNA Replication 1.Unwinding (Strand Separation) 1.Unwinding (Strand Separation): Helicase unwindingseparation a.Helicase: enzyme which catalyze the unwinding and separation (breaking H- Bonds) of the parental double helix. b. Single-Strand Binding Proteins b. Single-Strand Binding Proteins: proteins which attach and help keep the separated strands apart.

7. DNA Replication 2. Priming: RNA primers primers (RNA)RNA primers: before new DNA strands can form, there must be small pre-existing primers (RNA) present to start the addition of new nucleotides. PrimasePrimase: enzyme that polymerizes (synthesizes) the RNA Primer.

8. DNA Replication 3. Synthesis of the new DNA Strands: b.DNA PolymeraseRNA primer synthesis of a new DNA strand in the 5’ to 3’ direction b.DNA Polymerase: with a RNA primer in place, DNA Polymerase (enzyme) catalyze the synthesis of a new DNA strand in the 5’ to 3’ direction. RNAPrimer DNA Polymerase Nucleotide 5’ 3’

9. DNA Replication Leading Strand single polymer 5’ to 3’ direction Leading Strand: synthesized as a single polymer in the 5’ to 3’ direction. RNAPrimer DNA Polymerase Nucleotides 3’5’

10. DNA Replication Lagging Strand 5’ to 3’ directiondiscontinuously Lagging Strand: also synthesized in the 5’ to 3’ direction, but discontinuously against overall direction of replication. RNA Primer Leading Strand DNA Polymerase 5’5’ 5’ 3’ Lagging Strand 5’ 3’

11. DNA Replication Okazaki Fragments lagging strand. Okazaki Fragments: series of short segments on the lagging strand. Lagging Strand RNAPrimerDNAPolymerase 3’ 5’ Okazaki Fragment

12. DNA Replication 4. Joining: DNA ligase 3’ to 5’ end DNA ligase: a linking enzyme that catalyzes the formation of a covalent bond from the 3’ to 5’ end of joining stands. Example: joining two Okazaki fragments together. Lagging Strand Okazaki Fragment 2 DNA ligase DNA ligase Okazaki Fragment 1 5’ 3’

13. Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

14. Answer: DNA 3’-CGCATAC-5’

15. Replication Animation http://highered.mcgraw- hill.com/sites/0072437316/student_view 0/chapter14/animations.html#http://highered.mcgraw- hill.com/sites/0072437316/student_view 0/chapter14/animations.html#