DNA Structure

DNA Replication

Eukaryotic Chromosome Structure

Study Questions

DNA Structure, Replication and Eukaryotic Chromatin Structure Overheads

DNA Structure, Replication and Eukaryotic Chromatin Structure WWW Links

Genetic Topics

DNA Structure

Components of DNA

A DNA molecule is composed of a continuous string of deoxyribonucleotides. These nucleotides are composed of:

  • 5-Carbon sugar (deoxyribose)
  • Nitrogenous base (Adenine, Thymine, Guanine, Cytosine)
  • Phosphate group

Watson and Crick Model of DNA Structure

The following are the Watson and Crick conclusions regarding the structure of the DNA model.

  1. two single-stranded chains
  2. purine are opposite a pyrimidine
  3. chains held together by H-bonds
    • Guanine is paired with cytosine by three H-bonds
    • Adenine is paired with thymine by two H-bonds
  4. anti-parallel orientation of the two chains
  5. the molecule is stabilized by:
    • large # of H-bonds
    • hydrophobic bonding between the stacked bases

Types of DNA

  • A, B, C = right-handed helix
  • Z = left-handed helix (found in vitro under high salt conditions)

B is the major form that is found in the cell. But can type Z exist even though the cell doesn't have a high salt environment? Probably. Other features of the DNA molecule are present in vivo that can stabilize a Z-DNA structure under low salt or cellular conditions.

1. alternating purine/pyrimidine tracts

     G C                 A T
poly           or   poly          
     C G                 T A

2. 5-methyl-cytosine

Copyright © 1997. Phillip McClean