1.2

• Nucleotide


  A three-subunit molecule in which a pentose sugar is bonded to both a phosphate group and a nitrogen-containing heterocyclic base
• Nucleotide


  • More complex monomers than the monosaccharides of polysaccharides and the amino acids of proteins
• A block structural diagram for a nucleotide is: Phosphate - Sugar - Base
• Pentose sugars


  Ribose or 2-deoxyribose
• The only difference between ribose and 2-deoxyribose is that the -OH group at carbon 2 in ribose becomes -H in 2-deoxyribose
• RNA


  Nucleotides contain ribose sugar
• DNA


  Nucleotides contain 2-deoxyribose sugar
• Nitrogen-containing heterocyclic bases


  • Pyrimidine derivatives: Thymine, Cytosine, Uracil
  • Purine derivatives: Adenine, Guanine
• Pyrimidine is a monocyclic base with a six-membered ring, Purine is a bicyclic base with fused five- and six-membered rings
• Amine functional groups in the heterocyclic bases exhibit basic behavior (proton acceptors)
• Proteins are polypeptides, many carbohydrates are polysaccharides, and nucleic acids are polynucleotides
• Pentose ring atoms are designated with primed numbers, nitrogen-containing base ring atoms are designated with unprimed numbers
• Thiamine is a pyrimidine derivative, Caffeine is a purine derivative
• Adenine, guanine, and cytosine are found in both DNA and RNA, uracil is found only in RNA, and thymine usually occurs only in DNA
• Phosphate


  Derived from phosphoric acid, under cellular pH conditions it loses two hydrogen atoms to give a hydrogen phosphate ion
• Nucleotide formation


  1. Condensation occurs between sugar and base, and between sugar and phosphate, forming water

  2. Base is always attached at the C-1 position of the sugar, in a β configuration

  3. Phosphate group is attached to the sugar at the C-5 position through a phosphate-ester linkage
• Possible RNA nucleotides


  • Adenine, Cytosine, Guanine, Uracil
• Possible DNA nucleotides


  • Adenine, Cytosine, Guanine, Thymine
• Nucleotide nomenclature


  Names end in 5-monophosphate, base name precedes monophosphate, prefix deoxy- signifies deoxyribose sugar
• Abbreviations use one-letter symbols for bases, MP for monophosphate, and lower-case d for deoxyribose