Biological Molecules: Key Terms (AQA A Level Biology)

• There is much variety of life within and between organisms but the biochemical basis of life is similar for all living things
• The key molecules that are required to build structures that enable organisms to function are:
  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
  • Water

• Monomers are the smaller units from which larger molecules are made
• Polymers are molecules made from a large number of monomers joined together in a chain

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The key biological molecules for living organisms

• Carbohydrates, proteins, lipids and nucleic acids contain the elements carbon (C) and hydrogen (H) making them organic compounds
• Carbon atoms are key to the organic compounds because:
  • Each carbon atom can form four covalent bonds – this makes the compounds very stable (as covalent bonds are so strong they require a large input of energy to break them)
  • Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur
  • Carbon atoms can bond to form straight chains, branched chains or rings

• Carbon compounds can form small single subunits (monomers) that bond with many repeating subunits to form large molecules (polymers) by a process called polymerisation
• Macromolecules are very large molecules
  • That contain 1000 or more atoms therefore having a high molecular mass
  • Polymers can be macromolecules, however not all macromolecules are polymers as the subunits of polymers have to be the same repeating units

Carbohydrates

• Carbohydrates are one of the main carbon-based compounds in living organisms
• All molecules in this group contain C, H and O
• As H and O atoms are always present in the ratio of 2:1 (eg. water H₂O, which is where ‘hydrate’ comes from) they can be represented by the formula C_x (H₂O)_y
• The three types of carbohydrates are monosaccharides, disaccharides and polysaccharides

Types of Carbohydrates Table

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