3.3 DNA Replication

• 1. DNA helicase breaks the hydrogen bonds between the complementary bases, causing the 2 strands of the DNA to separate.
  2. Both strands act as template strands.
  3. Free DNA nucleotides are attracted to to their complementary bases (cytosine to guanine, adenine to thymine) and hydrogen bonds form between them.
  4. Once the new nucleotides have lined up, they are joined together by the enzyme DNA polymerase which forms phosphodiester bonds between adjacent nucleotides.
  5. Two identical strands of DNA are formed.
• DNA replicates in semi-conservative replication.
• It is called semi-conservative replication because the new DNA molecule is made of one old and one new strand.
• DNA helicase breaks the hydrogen bonds between complementary bases so the 2 strands of DNA break.
• DNA polymerase forms phosphodiester bonds between adjacent nucleotides.
• Cytosine-Guanine bonds have 3 hydrogen bonds.
• Adenine-Thymine bonds have 2 hydrogen bonds.
• A strand of DNA with lots of CG repeats is stronger than DNA with lots of AT because CG has three hydrogen bonds, and AT only has two, meaning they're stronger.
• DNA was thought to have replicated through semi-conservative, conservative, and dispersive. Semi-conservative is the actual way.
• In the semi-conservative model, both daughter molecules contain one old (parent) strand and one newly made strand.
• Describe the action of DNA helicase.

  DNA helicase breaks the hydrogen bonds between the complementary base pairs and so the two DNA strands separate.
• Describe the action of DNA polymerase.

  DNA polymerase forms phosphodiester bonds between adjacent nucleotides, reforms the DNA double strand.
• Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA.

  -DNA contains weak hydrogen bonding between bases so that DNA helicase can break them to split the strands easily.

  -DNA has two strands, so both can act as template strands.