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
, - 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
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