Nucleic acids

• Mononucleotides


  Structure: Pentose sugar, nitrogen-containing organic base, phosphate group
• DNA nucleotides


  • Deoxyribose sugar with hydrogen at 2' position
  • Phosphate group
  • One of four nitrogenous bases: adenine (A), cytosine(C), guanine(G) or thymine(T)
• RNA nucleotides


  • Ribose sugar with hydroxyl (OH) group at 2' position
  • Phosphate group
  • One of four nitrogenous bases: adenine (A), cytosine(C), guanine(G) or uracil (U)
• The presence of the 2' hydroxyl group makes RNA more susceptible to hydrolysis
• DNA is the storage molecule and RNA is the transport molecule with a shorter molecular lifespan
• Purines


  Nitrogenous bases with a double ring structure (adenine, guanine)
• Pyrimidines


  Nitrogenous bases with a single ring structure (cytosine, thymine, uracil)
• Phosphodiester bond formation


  1. Condensation reaction between phosphate group of one nucleotide and pentose sugar of next nucleotide

  2. Forms sugar-phosphate backbone
• DNA and RNA are polynucleotides made up of many nucleotides bonded together in a long chain
• DNA structure


  • Two antiparallel polynucleotide strands
  • Alternating deoxyribose sugars and phosphate groups in backbone
  • Nitrogenous bases project inwards
  • Complementary base pairing (A-T, G-C)
  • Forms a double helix
• RNA structure


  • Single polynucleotide strand
  • Alternating ribose sugars and phosphate groups in backbone
  • Nitrogenous bases project outwards
  • Contains uracil instead of thymine