DNA Replication

• Why must DNA be replicated?

  • So that both cells have identical copies of the entire genome
  • To ensure that all the daughter cells have the genetic information to produce the enzymes and other proteins that they need
• What is the method of DNA replication called?

  Semi-conservative replication
• Why is it known as semi-conservative replication?

  Because the original strand is split in two, and half of each new double helix is a strand that has come from the original DNA molecule

  • Half is 'conserved'
• Requirements for semi-conservative replication to take place:

  • The 4 types of nucleotide, each with their bases of Adenine, Guanine, Cytosine or Thymine present
• Requirements for semi-conservative replication to take place:

  • Both strands of the DNA molecule acting as a template for the attachment of the nucleotides
• Requirements for semi-conservative replication to take place:

  • The enzyme DNA polymerase
• Requirements for semi-conservative replication to take place:

  • A source of chemical energy required to drive the process
• What 4 requirements are there for DNA replication to take place?

  DNA template, DNA polymerase, nucleotides, and energy (ATP)
• DNA Replication: Step 1

  1. DNA helicase separates the two strands by breaking the hydrogen bonds between bases
• DNA Replication: Step 2

  • Each original strand acts as a template to build a new strand
• DNA Replication: step 3

  • Free nucleotides attach to a template strand through complimentary base pairing
• DNA Replication: Step 4

  • The free nucleotides are joined to the new strand with condensation reactions catalysed by the enzyme DNA polymerase, which forms hydrogen bonds between the bases on the two strands
• DNA Replication: Step 5

  • Finally, all the nucleotides are joined to form a complete polynucleotide chain using DNA polymerase
  • Each new strand contains one strand from the original DNA molecule and one new strand
• How structure of DNA is adapted to allow replication to occur efficiently:

  • The hydrogen bonds can be easily broken to allow both strands to be a template
• How structure of DNA is adapted to allow replication to occur efficiently:

  • Complimentary base pairing means that replication of the new strands should be accurate as the correct bases can ONLY pair with each other due to their structure
• Conservative replication - The original DNA serves as a complete template with the replicated DNA consisting of two completely new DNA strands
• Dispersive replication - The replicated DNA strands have old and new DNA scattered throughout them
• Semi-conservative replication - Each DNA strand acts as a template with each replicated DNA consisting of one original strand and one newly replicated strand
• What enzyme breaks the hydrogen bonds between bases?

  DNA helicase
• What enzyme adds new nucleotides to the new strand?

  DNA polymerase
• Why is one strand known as the template strand?

  Because it acts as a template for new nucleotides to create a new strand with the correct complimentary base pairing
• State the enzymes involved in DNA replication

  Helicase and polymerase
• What is the function of DNA polymerase?

  To join nucleotides together in condensation reactions
• What is the function of DNA helicase?

  To break the hydrogen bonds that hold the two strands of DNA together
• The semi-conservative replication of DNA ensures genetic continuity between generations of cells