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Chapter 7II. DNA Replication

DNA Replication Overview• Replication = DNA can make a copy of itself.• Each strand of the double helix serves as the

template or guide for the new strand (Similar to thenegative for a photo)

• Semi-conservative replication When replicationis complete each of the two daughter DNA moleculeswill have one old strand from the parent and onenewly made strand.

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DNA Replication

• Anti-parallel - The sugarphosphate backbones ofDNA run in oppositedirections

• One side runs 5’ to 3’• The other side runs 3’ to 5’

DNA Replication• DNA replication occurs at special sites called origins

of replication.– There can be be thousands of origins for a chromosome.

• Replication proceeds in both directions from theorigin at the replication fork (The Y shaped regionwhere the new DNA strands are being created)

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DNA Replication – Leading Strand• Helicase unwinds the double helix.• Single-Stranded Binding Proteins stabilize the unwound

DNA.• Primase – adds and RNA primer to the leading strand• DNA Polymerase replicates the leading strand in the 5' to 3'

direction by adding nucleotides.

DNA Replication – Lagging Strand• Helicase unwinds the double helix.• Single-Stranded Binding Proteins stabilize the unwound DNA.• Primase – adds and RNA primer to the lagging strand• DNA polymerase replicates the lagging strand in the 5' to 3' direction by

adding segments called Okazaki fragments.• DNA ligase joins the Okazaki fragments to create a single DNA strand.