Organic Subunits

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•  Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalised amino acid

Complex macromolecules may commonly be comprised of smaller, recurring subunits called monomers

  • Carbohydrates, nucleic acids and proteins are all comprised of monomeric subunits that join together to form larger polymers
  • Lipids do not contain recurring monomers, however certain types may be composed of distinct subunits (e.g. triglycerides)

Organic Monomers / Subunits

organic subunits


Carbohydrates are composed of monomers called monosaccharides ('single sugar unit')

  • Monosaccharides are the building blocks of disaccharides (two sugar units) and polysaccharides (many sugar units)
  • Most monosaccharides form ring structures and can exist in different 3D configurations (stereoisomers)

Examples of Common Monosaccharides



Lipids exist as many different classes that vary in structure and hence do not contain a common recurring monomer

However several types of lipids (triglycerides, phospholipids, waxes) contain fatty acid chains as part of their overall structure

  • Fatty acids are long chains of hydrocarbons that may or may not contain double bonds (unsaturated vs saturated)

Structure of a Typical Fatty Acid (Saturated)

fatty acid


Proteins are composed of monomers called amino acids, which join together to form polypeptide chains

  • Each amino acid consists of a central carbon connected to an amine group (NH2) and an opposing carboxyl group (COOH)
  • A variable group (denoted ‘R’) gives different amino acids different properties (e.g. may be polar or non-polar, etc.)

Structure of a Generalised Amino Acid

amino acid

Nucleic Acids

Nucleic acids are composed of monomers called nucleotides, which join together to form polynucleotide chains

Each nucleotide consists of 3 components – a pentose sugar, a phosphate group and a nitrogenous base

  • The type of sugar and composition of bases differs between DNA and RNA

Structure of a Generalised Nucleotide