Semi-conservative DNA replication

• Why is DNA replication described as semi-conservative?

  • When cell division occurs a copy of the cell's genetic information must be made
  • The DNA replicates forming a new DNA molecule
  • One strand of the new DNA molecule is made of the original DNA strand and the other is freshly made new one
  • Because half of the DNA is preserved from the previous round of DNA replication, the process is described as semi-conservative
• Describe the stages of DNA replication?

  1. DNA helicase unwinds the double helix by breaking the hydrogen bonds between the complementary base pairs
  2. One of the strands acts as a template for the synthesis of the other strand
  3. A complementary nucleotide attaches to the template strand by hydrogen bonding
  4. DNA polymerase catalyses formation of phosphodiester bonds between nucleotides, making a complementary strand which attaches to the template parent strand
  5. Two new daughter DNA molecules are produced each containing half of the original DNA molecule's DNA
• Why is it important that DNA polymerase is accurate?

  • It is important that DNA polymerase is accurate when copying the template strand to avoid placing an incorrect DNA nucleotide in the wrong place
• How to DNA polymerase prevent mistakes?

  • To prevent this, DNA polymerase proofreads the complementary strand as it moves along the DNA
• If a mistake in the complementary strand how does DNA polymerase react to this?

  • If a mismatch is found the DNA polymerase can snip out the incorrect nucleotide an replace it with the correct one
• What is the accuracy rate of DNA polymerase and what impact does it have?

  • DNA polymerase has an accuracy rate of 99% which means mistakes still occur
  • A mistake would lead to a change is the DNA base sequence referred to as a mutation
• What effect would a mutation have?

  • Mutations can be detrimental to organisms as a change to the specific sequence of amino acids for a protein, can cause it to fold differently and possibly lose its function