Nucleic Acids (College Board AP Biology)

Nucleotide Bases & Nucleic Acids

• DNA and RNA are nucleic acid polymers that are made up of many repeating units called nucleotides
• Each nucleotide is formed from:
  • A pentose sugar (a sugar with 5 carbon atoms)
  • A nitrogen-containing organic base (with either 1 or 2 rings of atoms)
    • There are four bases in DNA: adenine (A), cytosine (C), guanine (G) and thymine (T)
    • In RNA, a fifth base, uracil (U), appears in place of thymine
  • A phosphate group (this is acidic and negatively charged)
• The base and phosphate group are both covalently bonded to the sugar

Diagram of the General Structure of a DNA Nucleotide

The basic structure of a nucleotide

Components of Nucleic Acid Structure

• Nucleotide bases join together in chains to form DNA or RNA strands
• The phosphate group of one nucleotide forms a covalent bond to the pentose sugar of the next one
  
  • This forms a "sugar phosphate backbone" with a base linked to each sugar
• The polymer of nucleotides is known as a strand
• Nucleotide bases can be joined in any combination/sequence
• The sequence of nucleotide bases acts as a store of genetic information for an organism

RNA & DNA

• RNA & DNA different in structure and function
  • DNA is double-stranded, RNA is usually single-stranded
  • DNA contains the bases A, T, C, and G, whereas RNA contains the bases A, U, C and G
  • DNA has a deoxyribose sugar whereas RNA has a ribose sugar
  • The similarities and difference between DNA and RNA are dealt with in Topic 1.6 Nucleic Acids