Biological molecules, water and inorganic ions definitions

Carbohydrate structure and function

Monosaccharide

A single sugar unit, the monomer from which disaccharides and polysaccharides are built.

Monomer

A small molecule from which a larger one is built by joining many of them together.

Polymer

A large molecule made of many similar monomers joined together.

Macromolecule

A very large molecule with a high relative molecular mass, such as a polysaccharide, a protein, a nucleic acid or a triglyceride.

Condensation

A reaction that joins two molecules with a covalent bond and releases a molecule of water.

Hydrolysis

A reaction that breaks a covalent bond between two molecules using a molecule of water.

Glycosidic bond

The covalent bond formed by condensation between two monosaccharides, joining them through an oxygen atom.

Disaccharide

Two monosaccharides joined by a glycosidic bond.

Polysaccharide

Many monosaccharides joined by glycosidic bonds into one large molecule.

Tensile strength

The greatest pulling force a material can withstand before it breaks, divided by its cross-sectional area.

Retting

Soaking or leaving plant stems in damp conditions so that microorganisms digest the pectins binding the fibres to the tissue around them, and the fibres can be separated.

Sustainability

Using resources to meet present needs in a way that does not reduce the ability of future generations to meet theirs.

Biodegradable

Able to be broken down by microorganisms into simple substances such as carbon dioxide and water.

Polylactic acid

A plastic made by fermenting glucose from plant starch into lactic acid and polymerising it; abbreviated to PLA.

Lipids: triglycerides, phospholipids and ester bonds

Lipid

A biological molecule that is largely non-polar, insoluble in water and soluble in organic solvents such as ethanol.

Triglyceride

One glycerol molecule joined to three fatty acids by three ester bonds.

Ester bond

The covalent bond formed by condensation between a hydroxyl group of glycerol and the carboxyl group of a fatty acid.

Hydrophilic

Attracted to water: charged or polar, so it interacts with water molecules.

Hydrophobic

Not attracted to water: non-polar, so it is excluded from water rather than dissolving in it.

Water and inorganic ions

Polar molecule

A molecule with an uneven distribution of charge, so that one part is slightly negative and another slightly positive.

Hydrogen bond

A weak attraction between a slightly positive hydrogen atom and a slightly negative atom such as oxygen or nitrogen, in another molecule or another part of the same molecule.

Specific heat capacity

The energy needed to raise the temperature of one kilogram of a substance by one kelvin.

Latent heat of vaporisation

The energy needed to change one kilogram of a liquid into a gas without a change in temperature.

Inorganic ion

An ion containing no carbon, apart from carbonate and hydrogencarbonate, present in solution in cytoplasm and body fluids, often in very small amounts, and each with a specific role.

Protein structure and function

Amino acid

A molecule containing an amine group, a carboxyl group and a variable side chain attached to the same carbon.

Polypeptide

A chain of amino acids joined by peptide bonds.

Protein

One or more polypeptides folded into a specific three-dimensional shape.

Primary structure

The sequence of amino acids in a polypeptide, held by peptide bonds.

Secondary structure

The regular coiling or pleating of the backbone into an α-helix or β-pleated sheet, held by hydrogen bonds between the C=O of one peptide group and the N–H of another.

Tertiary structure

The overall three-dimensional fold of a single polypeptide, held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions between side chains.

Quaternary structure

The arrangement of two or more polypeptides, and any non-protein groups, in a functioning protein.

Denaturation

The loss of a protein's specific three-dimensional shape through disruption of the hydrogen bonds, ionic bonds and hydrophobic interactions holding it, so the function is lost, while the primary structure is unchanged.