1.6.A—Describe the structure and function of DNA and RNA

Describe the structure and function of DNA and RNA.

• In nucleic acids (DNA and RNA), biological information is encoded in sequences of nucleotide monomers. Each nucleotide has the following structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil).
• Nucleic acids have a linear sequence of nucleotides that have ends, defined by the 3’ (three prime) hydroxyl and 5’ (five prime) phosphates of the sugar in the nucleotide. During nucleic acid synthesis, nucleotides are added to the 3’ end of the growing strand, resulting in the formation of covalent bonds between nucleotides.
  • Exclusion: The molecular structure of specific nucleotides is beyond the scope of the AP Exam.
• DNA is structured as an antiparallel double helix, with two strands of nucleotides running in opposite 5’ to 3’ orientation. In DNA, adenine nucleotides pair with thymine nucleotides via hydrogen bonds (A-T), and cytosine nucleotides pair with guanine nucleotides via hydrogen bonds (C-G). In RNA, adenine pairs with uracil (A-U).
• Structural differences between DNA and RNA include:
  • i. DNA contains the sugar deoxyribose, and RNA contains the sugar ribose.
  • ii. DNA contains the nitrogenous base thymine, and RNA contains the nitrogenous base uracil.
  • iii. DNA is typically double stranded, while RNA is typically single stranded.