Nucleic Acids I

• Nucleic Acids


  The study of nucleic acids is at the forefront of chemistry and biology. The knowledge of the chemical makeup of DNA and RNA has allowed for the sequencing of these macromolecular polymers — the genetic code. These advances have given rise to the new science of molecular biology and the potential health advances that this will bring.
• Primary Structure of Nucleic Acids


  • Bases
  • Nucleosides
  • Nucleotides
  • Single strands

  
• Bases


  Derived from purine or pyrimidine. In the correct tautomeric forms, these heterocycles have hydrogen bond donors and acceptors which allows them to form H-bonds with each other and recognise each other.

  
• Tautomerism


  DNA nucleotides recognise each other by patterns of hydrogen bonds. The major tautomer of each base must be known to know the location of hydrogen bond donors and hydrogen bond acceptors.

  
• Pyrimidines


  Comprise three of the five common bases found in DNA and RNA.

  
• Purines


  Comprise two of the five common bases found in DNA and RNA.

  
• Hydrogen bond donors and acceptors


  • Hydrogen donors are H attached to an electronegative atom: in this case, it's bonded to a N. To be an acceptor, the atom needs to contain a lone pair.
• Nucleosides


  A heterocyclic base linked to a sugar related to ribose. Nucleosides are a type of glycoside, which are stable and the ring doesn't open.

  
• 1. ribose


  • Locked in the furanose conformation by the bond from C1 of the sugar to: N1 of C, T or U or N9 of A or G
  • All of the above ribose based nucleosides are found in RNA (ribonucleic acid)
  • If the OH groups are on the same side of the ring/as the anomeric centre, it's beta. If they were on opposite sides, it would be alpha.
  • DNA is deoxyribonucleic acid hence the nucleosides found in DNA are missing an oxygen on the ribose sugar ring. The hydroxyl is missing from the 2' position.

  
• Nucleotides


  Phosphate esters of nucleosides. Phosphate groups are attached to free hydroxyl groups on the ribosyl sugar. Nucleotides play many roles in biochemistry other than just making up nucleic acids. The phosphate groups give the nucleotides overall negative charges at physiological pH compared to the positive charges on the bases.

  
• Nucleotides From DNA and RNA


  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T)
  • Uracil (U)

  
• Other Roles of Nucleotides


  • Activated intermediates in biosynthesis
  • Movement of energy within an organism (ATP)
  • Components of major coenzymes (NAD+, FAD, coenzyme A)
  • Metabolic regulators (cAMP)
• Adenosine triphosphate (ATP)


  A very important species in metabolism and the generation of metabolic energy. It's a triphosphate.

  
• Acetyl coenzyme A (CoA)


  A carrier of acetyl groups which are used during biosynthesis
• NAD+


  An important coenzyme
• Cyclic nucleotides


  Nucleotides can occur in cyclic forms with the phosphate linking two hydroxyl groups on the ribose. Certain hormones cause the cyclisation of AMP to cAMP. cAMP acts as an intracellular messenger leading to the mediation of the physiological effect triggered by the hormone.