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DNA Replication

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DNA Replication Converting a single DNA helix into two identical copies. Described as semi conservative replication. New DNA Strands Helicase enzyme splits and ... – PowerPoint PPT presentation

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Title: DNA Replication


1
DNA Replication
  • Converting a single DNA helix into two identical
    copies.
  • Described as semi conservative replication.

2
New DNA Strands
  • Helicase enzyme splits and unwinds the two
    stranded DNA.

3
Naming DNA Direction
  • DNA strands are recognised and named according to
    the carbon atom exposed at the end of the strand.

C5
C1
C4
C2
C3
4
Forming a New Strand
  • A topoisomerase enzyme cuts the DNA
    strand allowing it to twist and relieve
    pressure.
  • An enzyme RNA polymerase is used to add a short
    section of RNA to start the process.

5
Addition of nucleotides
  • An enzyme DNA polymerase III is used to catalyse
    the addition of DNA nucleotides.
  • When nucleotides are added to a new strand they
    can only do so in a 5 (5 prime) to 3 direction.

3 5 3 5
6
Base Pairing
  • Nucleotides are added. A joins to T, C joins
    to G.

7
New DNA Strands
  • The leading strand (red) is synthesised
    continuously.
  • The lagging strand (pink) is formed in
    segments called okazaki fragments.
  • An enzyme DNA polymerase I replaces the RNA
    primers with DNA

8
Filling the Gaps
  • The DNA strands continue to form in a 5 to 3
    direction.
  • An enzyme DNA Ligase is used to fill in the gaps
    in the okazaki fragments with nucleotides.

9
Completion
  • When DNA replication is complete two molecules
    are formed.
  • Because half of each strand is new and half
    original it is called semi conservative
    replication.

10
Questions
  • What is the purpose of DNA replication?
  • Name the enzyme that splits and unwinds DNA.
  • Why is the 5 end of a DNA strand given this
    name?
  • What is the role of the topoisomerase enzyme?

11
Questions continued
  • How is the addition of nucleotides started?
  • What is the role of DNA polymerase III ?
  • In what direction are nucleotides added?
  • What are the base pairing rules?
  • Why does this occur?

12
Questions continued
  • What name is given to the continuously formed
    strand?
  • Why is the lagging strand formed in fragments?
  • What name is given to the DNA fragments?
  • Which enzyme joins the fragments together?
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