Replication copies the genetic information

What is replication?

• Making another copy of DNA

When does replication take place?

• During synthesis of interphase

• Makes a copy of itself during mitosis and meiosis

Why does replication happen?

• Done in order to ensure all cells in body have same information

Watson/Crick model gave clues to how DNA replicates

• Base pairing rule

• If one strand is known, the sequence of the other strand is also known

• Therefore, a single strand of DNA can serve as a template for a new strand

Proteins carry out the process of replication

• Helicase (enzymes)

  • unzip double helix by breaking hydrogen bonds

  • Hold strands apart

• DNA polymerases (enzymes)

  • Enzymes that bond free nucleotides to each template strand of DNA

Steps in DNA replication

• 1. Double helix is opened by the enzyme helicase at the origins of replication

  • helicase breaks open the hydrogen bonds between bases

• 2. Free nucleotides are added to form base pairs according to Chargaff’s rules by an enzyme called DNA polymerase

• 3.DNA polymerase causes the hydrogen bonds to form new rungs again and sugar phosphate bonds form to create new side

  • resulting in two new identical DNA molecules

    • Each have one original side and one new side

  • Semi-conservative replication

Replication is fast and accurate

• Fast:

  • 50 nucleotides added per second

  • starts at many origins of replication

• Accurate:

  • DNA polymerase -- spell check

    • Detects and removes incorrect nucleotide

    • replaces with correct nucleotide

    • So that only 1 in every 1,000,000,000 nucleotides is wrong