BIOL1006 Lecture Notes - Lecture 6: Hydrogen Bond, Dna Replication, Pyrimidine
Document Summary
Dna has a double-helix structure, with sugar and phosphate on the outside of the helix, forming the sugar- phosphate backbone of the dna. The nitrogenous bases are stacked in the interior in pairs, like the steps of a staircase; the pairs are bound to each other by hydrogen bonds. The two strands of the helix run in opposite directions, so that the 5 carbon end of one strand faces the 3 carbon end of its matching strand. This antiparallel orientation is important to dna replication and in many nucleic acid interactions. The phosphate backbone is on the outside, and the bases are on the inside. Each base from one strand interacts via hydrogen bonding with a base from the opposing strand. A certain purine can only pair with a certain pyrimidine. This means adenine pair with thymine, and guanine pairs with cytosine. This is known as the base complementary rule because the dna strands are complementary to each other.
