the fun side of biochemistry

Nucleotides and Nucleic Acids

Here are some brief points on Nucleotides and Nucleic Acids

NUCLEIC ACIDS

Functions of nucleic acids are:

  • Informational biomolecules – DNA, RNA

–       Function as polymers in the storage and transmission (expression) of the genetic information. (giant molecules)

  • Electron carriers – NAD+, FAD
  • Carriers of high energy intermediates

–       UMP, CMP, GTP

  • Energy currency of the cell – ATP
  • Signaling molecules – cAMP, AMP, etc

The monomeric units of a nucleotide polymer contain 3 components:

  1. 1.    A nitrogenous heterocyclic base, either:
  • Pyrimidine
  • Purine
  1. 2.    A pentose sugar which is either:
  • Ribose (furanose form)
  • 2-deoxy-ribose (furanose form)
  1. 3.    A phosphoric acid group in ester linkage at C-5 of the pentose
  • The phosphoester bond

Double Helical DNA:

  • 2 complementary anti-parallel strands – right-hand coil along a common axis
  • Held together by H-bonds – A-T & G-C
  • Bases on the interior – planes are perpendicular to helix axis
  • Sugar and P-groups on the outside, exposed to H2O
  • Sugar rings almost at right angles to the planes of the bases

Nitrogenous bases:

  • DNA – adenine, guanine, cytosine, thymine

–       A, G, C, T

  • RNA –  adenine, guanine, cytosine, uracil

–       A, G, C, U

  • A and G – purines

–       Purines are bicyclic fused rings of a pyrimidine & a 5-membered imidazole

  • U, T, C  – pyrimidines

–       6-membered ring

Chargaff’s Rules

  • Analysis of DNA from most species –

–       4 bases are not equal

–       Base composition varies between species

  • But, different tissues of the same species

–       Same base comp.

  • And always: A = T and G = C

–       sum of purines = sum of pyrimidines

  • Related species, similar base composition

 

NUCLEOTIDES

  •   nucleotides are the building blocks for DNA and RNA
  •   nucleotides are carriers for activated intermediates
  •   nucleotides are structural components of coenzyme A, FAD, NAD+, and NADP+
  •   defects in nucleotide metabolism are associated with several common and rare human disorders
  •   several drugs used to treat cancer and bacterial infections function at the level of nucleotide metabolism
  • Nucleotides are composed of a nitrogenous base, a pentose monosaccharide, and 1, 2, or 3 phosphate groups.
  • The nitrogenous bases are derived from 2 families called purines and pyrimidines.

There are 5 common bases found in DNA and RNA:

  •   Purines Adenine and Guanine common to both DNA and RNA
  •   Pyrimidines Thymine and Cytosine are found in DNA
  •   Pyrimidines Cytosine and Uracil are found in RNA

Nucleosides

  • Addition of a pentose sugar to the base produces a nucleoside. Base + ribose = nucleoside
  • Addition of a ribose sugar to the bases A, G, C, T, and U produces adenosine, guanosine, cytidine, thymidine, and uridine, respectively.
    •   If the pentose sugar is a deoxyribose, then a deoxyribonucleoside is produced.

Nucleotides

  • Addition of either 1, 2, or 3 phosphate groups to a nucleoside produces a nucleoside.  Monophosphate, nucleoside diphosphate, or a nucleoside triphosphate, respectively.  Base + sugar + phosphate = nucleotide.  
  • The phosphate groups are responsible for the negative charges associated with RNA and DNA.
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