DNA replication

• DNA replication must occur before any type of cell division can happen
• For DNA replication to occur :

  
  

  presence of all 4 DNA nucleotides with nitrogenous bases

  correct enzymes

  source of energy (ATP)
• Watson and Crick discovered the double helix structure of DNA
• Watson and Crick had two theories :

  • Conservative method
  • semi-conservative method
• The two enzymes involved in DNA replication are :

  
  

  >DNA helicase

  >DNA polymerase
• DNA helicase breaks hydrogen bonds between complementary bases, which is the process of unwinding the DNA helix
• DNA ligase catalyses the formation of a phosphodiester bond between the activated nucleotides
• The free nucleotides are also known as activated nucleotides
• Activated nucleotides have three phosphate groups , not one .
• When phosphodiester bonds form, the activated nucleotide looses their extra two phosphate groups
• Activated nucleotides loosing their two extra phosphate groups provides energy for the reaction
• When nucleotides first line up with their complimentary bases , they are only being held by hydrogen bonds not phosphodiester bonds
• semi-conservative method : each of the two copies contains one original strand and one new strand of DNA
• Conservative method : a DNA double helix is formed containing two new strands