Eukaryotic Chromosome Structure

DNA Structure

Components of DNA

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

Watson and Crick Model of DNA structure

1. 2 chains
2. purine 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'-------->3'
   • 3'<--------5'
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.

• alternating purine/pyrimidine tracts

		       G C                       A T
		poly d           or       poly d           
		       C G                       T A

• 5-methyl-cytosine