Nucleic Acids (College Board AP® Biology): Study Guide

Comparing DNA & RNA

Similarities

• DNA and RNA are polynucleotides – it is made up of many nucleotides linked together in a chain

• Both DNA & RNA have three components:

  • Deoxyribose sugar (a pentose sugar)

  • A phosphate group

  • A nitrogenous base

• These three components form nucleotide units that are connected by covalent bonds

• Once bonded the nucleotide units form a linear molecule with 5’ & 3’ ends, with the nitrogenous bases perpendicular to the sugar-phosphate backbone

Differences

• There are several structural differences between DNA & RNA:

  • DNA contains deoxyribose while RNA contains ribose

  • DNA nucleotides contain the nitrogenous bases

    • adenine (A),

    • guanine (G),

    • cytosine (C)

    • thymine (T)

  • RNA nucleotides contain the nitrogenous bases

    • adenine (A)

    • guanine (G)

    • cytosine (C)

    • uracil (U), a key difference to DNA

  • DNA is usually double-stranded whereas RNA is usually single-stranded

  • DNA polynucleotide chains are very long whereas RNA are relatively short compared to DNA