1.3 3

• DNA replication


  The process by which a DNA molecule makes an identical copy of itself
• DNA replication


  • It is a semiconservative process
  • The original double helix unzips and new nucleotides align along each strand
  • Each new double helix contains one strand of the original DNA and one strand made up of new material
• Semiconservative DNA replication


  1. DNA helicase unzips the two strands of the DNA molecule

  2. DNA polymerase lines up and catalyses the linking up of the nucleotides along the template strand

  3. DNA ligase catalyses the formation of phosphodiester bonds between the two strands of DNA
• The result of semiconservative DNA replication is two new strands of DNA identical with the original piece
• The evidence from the experiments by Meselson and Stahl


  Supported the semiconservative model of DNA replication and disproved the conservative replication model
• DNA helicase


  An enzyme involved in DNA replication that unzips the two strands of the DNA molecule
• DNA polymerase


  An enzyme involved in DNA replication that lines up and catalyses the linking up of the nucleotides along the template strand
• DNA ligase


  An enzyme involved in DNA replication that catalyses the formation of phosphodiester bonds between the two strands of DNA
• The double helix structure of DNA is important for its role as the genetic material of the cell
• The chains of nucleotides in DNA fit together perfectly as long as cytosine and guanine, adenine and thymine are always matched together
• The exposed bases in the unzipped DNA molecule attract free DNA nucleotides and new hydrogen bonds are formed between matching base pairs
• The new DNA molecules automatically coil up into the double helix as weak hydrogen bonds form within the structure