Nucleic acids

• Deoxyribonucleic acid (DNA)


  Used to store genetic information
• Ribonucleic acid (RNA)


  Used to transfer genetic information
• Both DNA and RNA are polymers made of nucleotide monomers
• DNA nucleotide components

  • Phosphate
  • Sugar
  • Nitrogenous bases
• DNA

  • Made of 2 anti-parallel polynucleotide chains
  • Backbone made from phosphodiester bonds
  • Hydrogen bonds hold nitrogenous bases together
  • A-T have 2 hydrogen bonds, C-G have 3 hydrogen bonds
  • Nitrogenous bases contain nitrogen, phosphorus, carbon, hydrogen and oxygen
  • The 4 nitrogenous bases are adenine, thymine, guanine and cytosine
• Nucleic acids

  The base pairing ensures the ends of the polynucleotide chain are the same distance apart
• DNA structure

  • Long polynucleotide to store a lot of genetic information
  • Double helix with nitrogenous bases in the centre held by sugar backbone
  • Phosphodiester bonds add stability to double helix
  • Weak hydrogen bonds between bases allow polynucleotide chains to be easily separated
• Purine bases (adenine and guanine) pair with pyrimidine bases (thymine and cytosine)
• RNA

  • Polynucleotide vs DNA
  • Sugar is ribose
  • Contains 4 nitrogen bases, including uracil instead of thymine
  • Single-stranded
  • Shorter than DNA
• Types of RNA

  • mRNA
  • tRNA
  • rRNA
• DNA replication

  1. Enzyme DNA helicase breaks hydrogen bonds between 2 polynucleotide chains

  2. Original strands act as template for synthesis of new strands

  3. Free complementary nucleotides attracted to complementary bases

  4. DNA polymerase uses condensation reaction to form phosphodiester bonds
• DNA replication is semi-conservative, with 1 original strand and 1 new synthesised strand
• RNA bases are nitrogenous, including uracil instead of thymine
• Bacteria can use nitrogen-15 to make new DNA molecules