A.Molecular Structure of DNA
➢ Made up of repeated units of nucleotides
- Each nucleotide has:
■ 5-carbon sugar
● Pentagon shaped
● Called deoxyribose
● Linked to phosphate and nitrogenous base
■ Phosphate
■ Nitrogenous base
● Adenine - Purine (double-ringed)
● Guanine - Purine
● Cytosine - Pyrimidine (single-ringed)
● Thymine - Pyrimidine
● Purines always pair up with pyrimidines to keep DNA width consistent
➢ Nucleotides linked together by phosphodiester bonds that make up the sugar-phosphate backbone
➢ Double helix structure discovered by scientists Watson, Crick, and Franklin
- Nobel prize earned for discovery
- Franklin used X-Ray crystallography in its discovery
➢ Base pairing (Chargaff’s Rules)
- Each base can only bond with a specific complementary base
■ A-T
■ C-G - Specific rations of each nucleotides in the same species
➢ Complementary strands
➢ Strands are antiparallel
- Run in opposite directions
- 5’ and 3’ end named after carbons that end them
■ 5’ has phosphate group
■ 3’ has hydroxyl group - Strands linked by hydrogen bonds
