Biological Molecules: Key Terms (AQA A Level Biology)

Biological Molecules: Key Terms

• 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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