Nucleic Acids

What Are Nucleic Acids?

• Nucleic acids are macromolecules that store and transmit genetic information.

• Made of repeating subunits called nucleotides.

• Main types:

  • DNA (deoxyribonucleic acid)

  • RNA (ribonucleic acid)

Monomers: Nucleotides

Each nucleotide has three parts:

• Phosphate group

• 5-carbon sugar

  • Deoxyribose (DNA)

  • Ribose (RNA)

• Nitrogenous base

Nitrogenous Bases

• Purines (two rings):

  • Adenine (A)

  • Guanine (G)

• Pyrimidines (one ring):

  • Cytosine (C)

  • Thymine (T) – DNA only

  • Uracil (U) – RNA only

Structure of DNA

• Shape: Double helix

• Made of two antiparallel strands

• Sugar-phosphate backbone on the outside

• Bases face inward and pair via hydrogen bonds

  • A pairs with T

  • C pairs with G

• Function:

  • Stores hereditary information

  • Instructions for making proteins

Structure of RNA

• Usually single-stranded

• Uses ribose sugar

• Uses uracil (U) instead of thymine

• Main types:

  • mRNA – carries genetic code

  • tRNA – brings amino acids

  • rRNA – makes up ribosomes

Bonds in Nucleic Acids

• Phosphodiester bonds

  • Covalent bonds linking nucleotides

  • Form the sugar-phosphate backbone

• Hydrogen bonds

  • Hold complementary bases together in DNA

Dehydration Synthesis and Hydrolysis

• Nucleotides are joined by dehydration synthesis

  • Water released when bonds form

• Broken down by hydrolysis

  • Water added to break bonds

• (In cells, DNA/RNA assembly is enzyme-driven and specialized)

Functions of Nucleic Acids

• Store genetic information

• Transmit hereditary traits

• Direct protein synthesis

• Enable cell growth, repair, and reproduction

Structure Determines Function

• Sequence of bases = genetic code

• Complementary base pairing ensures accurate replication

• Hydrogen bonds allow DNA strands to separate during copying