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. two single-stranded chains purine are opposite a pyrimidine chains held together by H-bonds Guanine is paired with cytosine by three H-bonds Adenine is paired with thymine by two H-bonds anti-parallel orientation of the two chains 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