DNA double helix and nucleotide pairing

Summary

DNA is a molecule made of two polynucleotide strands twisted into a double helix, resembling a ladder spiraled around its axis. The sides of the ladder consist of alternating deoxyribose sugars and phosphate groups, while the rungs are formed by pairs of nitrogenous bases. Each nucleotide contains a sugar, a phosphate group, and one nitrogenous base: adenine (A), thymine (T), cytosine (C), or guanine (G). The bases pair in a specific, complementary manner: adenine pairs only with thymine through two hydrogen bonds, while cytosine pairs only with guanine through three hydrogen bonds. The order of these base pairs stores genetic information. During DNA replication, the two strands separate as hydrogen bonds are broken, and DNA polymerase builds a complementary strand for each original strand, producing two DNA molecules that each contain one original strand and one newly synthesized strand.

Key Points

• 1

  DNA consists of two complementary polynucleotide strands arranged in a double-helix structure.

• 2

  A nucleotide is made of a deoxyribose sugar, a phosphate group, and one nitrogenous base.

• 3

  Adenine pairs with thymine using two hydrogen bonds, while cytosine pairs with guanine using three hydrogen bonds.

• 4

  Complementary base pairing allows DNA to store genetic information and be copied accurately during replication.