DNA replication

• Deoxyribonucleic acid (DNA)


  Codes for sequence of amino acids in the primary structure of protein, determines final 3D structure & protein function
• Polynucleotides


  Polymers of nucleotides, created via condensation reaction between deoxyribose and phosphate group, forming phosphodiester bonds (strong covalent bonds)
• DNA


  • Strong bonds between sugar and phosphate groups hold the polymer together, forming the sugar-phosphate backbone
  • Occurs in pairs, joined by hydrogen bonds between bases
  • Double helix structure
• Hydrogen bonds


  Only form between complementary base pairs: Adenine & Thymine (2 H bonds), Cytosine & Guanine (3 H bonds)
• Nucleotide


  Made up of deoxyribose (pentose sugar), nitrogenous base (can be Adenine, Thymine, Cytosine or Guanine), and one phosphate group
• DNA replication


  1. DNA helicase breaks hydrogen bonds between complementary base pairs, causing double helix to unwind and strands to separate

  2. Each strand acts as template, free floating nucleotides attracted to complementary base pairs

  3. Adjacent nucleotides joined by condensation reaction catalysed by DNA polymerase, forming phosphodiester bonds

  4. Daughter DNA contains one original strand and one newly synthesised
• Stable DNA structure due to sugar-phosphate backbone and double helix
• Weak hydrogen bonds allow easy unzipping of two strands during replication
• Large DNA molecule allows it to carry lots of genetic information
• Complementary base pairing allows identical copies to be made during replication