Semi-Conservative DNA Replication

• What is DNA like in eukaryotic cells?

  • Found in the nucleus as chromosomes
  • Humans- 23 pairs of chromosomes
  • Each chromosome is a single linear molecule of DNA which is wound up tightly
  • Chromosomes help to make DNA compact to fit inside the nucleus.
• What do cells receive when cells divide to form new cells by mitosis or meiosis?

  A copy of the DNA
• DNA must be able to make an exact copy of itself- this is called DNA replication.
• What are the steps in DNA replication?

  1. DNA helicase breaks the hydrogen bonds between the bases in the double helix, which unwinds the DNA to separate strands and expose unpaired bases
  2. ATP activates free nucleotides in the nuclues
  3. Free nucleotides complementary base pair with the exposed bases
  4. To form new strands, nucleotides are joined together by phosphodiester bonds, which is catalysed by DNA polymerase
  5. Two new DNA molecules ate now formed- each contained one new and one original DNA strand
  6. This is called semi-conservative DNA replication
• What are some key points to remember about DNA replication?

  • It’s semi-conservative - each new DNA molecule has one new strand and one original strand of DNA
  • Both strands of DNA in the original molecule act as a template
  • The two new DNA molecules that form are identical
  • DNA helicase breaks hydrogen bonds between DNA strands to separate strands and expose bases
  • DNA polymerase catalyses the complementary base pairing of free nucleotides to exposed bases and the formation of phosphodiester bonds to join the nucleotides together in the new DNA strands.