DNA replication

• why must chromosomes make copies of themselves?

  so that when cells divide, each daughter cell receives an exact copy of the genetic information - this copying of DNA is called replication and takes place in the nucleus during interphase
• where does DNA replication take place?

  in the nucleus
• when does DNA replication take place?

  during interphase
• what were the 3 initial possibilities imagined for the mechanism of DNA replication?

  • conservative replication
  • semi-conservative replication
  • dispersive replication
• what happens during conservative replication?

  the parental double helix remains intact (i.e. is conserved) and a whole new double helix is made
• what happens during semi-conservative replication?

  the parental double helix separates into 2 strands, each of which acts as a template for synthesis of a new strand
• what happens during dispersive replication?

  the 2 new double helices contain fragments from both strands of the parental double helix
• what was done to test which hypothesis of DNA replication was correct?

  experiments were carried out
• what did Watson and Crick to do test which hypothesis about DNA replication was correct?

  • when they built their model of the structure of DNA, they realised that complimentary base pairs implied that if the 2 strands were separated, they would make another complimentary strand
  • 2 new identical molecules would form, each with one old strand and one newly synthesised strand - this is semi-conservative replication
• what is semi-conservative replication?

  mode of DNA replication in which each strand of a parental double helix acts as a template for the formation of a new molecule, each containing one original, parental stand, and one newly synthesised, complimentary daughter strand
• what is a template?

  a molecule of which the chemical structure determines the chemical structure of another molecule
• what is this an image of?

  conservative replication

  
• what is this an image of?

  disperse replication

  
• what is this an image of?

  semi-conservative replication