JMU Bio 140 Chemical Composition & Structure of DNA Notes

3.1 Chemical composition & structure of DNA
- Nucleotides:
- 5 carbon sugar
- Base
- One or more phosphate groups




-
- Phosdiester bonds: linked to a 5’ phosphate group to a 3’ hydroxyl group
- Polarity: one end of a structure differs from another, 5’ to 3’
- 5’ AGCT 3’ = 3’TCGA 5’
Purine bases: double ring structure
- A& G
- Pyrimidine bases: single ring structure
- T&C
- A= T
- G=C

,- Nucleoside: SUGAR AND BASE ONLY




- Watson & Crick build another model of DNA
- X-ray crystallography of DNA = Franklin and Wilkins
- Determined DNA had helical structure with repeating structure
along its length
- Space -filling model, each atom is represented as a color-coded
sphere
- Form of a helix, 10 base pairs per complete turn, Erwin Chargaff,
DNA extracted from cells of a wide variety of organisms all have a
characteristics:
- # of molecules of a nucleotide base adenine (A) = # of molecules in
thymine (T)
- # of molecules of guanine (G) = # of molecules in cytosine ©
- Jerry Donohue and John Griffth, determined that A paired with T and G
paired with C

, - Form of a helix, 10 base per complete turn
- Major groove: backbones are far apart
- Minor groove: backbones are closer together




- DNA strands are antiparallel, opposite directions
- 3’ to 5’ or 5’ to 3’
- Complementary bases
- G & C = 3 hydrogen bonds
- A & T = 2 hydrogen bonds
- Hydrogen bond in DNA is formed when electronegative atom (O or N) in
one base shares a hydrogen atom with another electronegative atom in
the base
- Weak bonds
- Base stacking: stabilizing hydrophobic interactions between bases in same
strand of DNA, tightly packed