Biological molecules (Chap 2)

Macromolecule a

a large molecule such as a polysaccharide, protein or nucleic acid

Polymer

a giant molecule made from many similar repeating subunits joined together in a chain; the subunits are much smaller and simpler molecules known as monomers; examples of biological polymers are polysaccharides, proteins and nucleic acids

Monomer

a relatively simple molecule which is used as a basic building block for the synthesis of a polymer; many monomers are joined together by covalent bonds to make the polymer, usually by condensation reactions; common examples of monomers are monosaccharides, amino acids and nucleotides

Condensation reaction

a chemical reaction involving the joining together of two molecules by removal of a water molecule.

Hydrolysis

a chemical reaction in which a chemical bond is broken by the addition of a water molecule; commonly used to break down complex molecules into simpler molecules

Monosaccharide

a molecule consisting of a single sugar unit and with the general formula (CH2O)n.

Disaccharide

a sugar molecule consisting of two monosaccharides joined together by a glycosidic bond

Glycosidic bond

a C-O-C link between two sugar molecules, formed by a condensation reaction; it is a covalent bond

Benedict's test

a test for the presence of reducing sugars; the unknown substance is heated with Benedict's reagent, and a change from a clear blue solution to the production of a yellow, red or brown precipitate indicates the presence of reducing sugars such as glucose

Polysaccharide

a polymer whose subunits are monosaccharides joined together by glycosidic bonds

Glycogen

a polysaccharide made of many glucose molecules linked together, that acts as a glucose store in liver and muscle cells

Cellulose

a polysaccharide made from beta- glucose subunits; used as a strengthening material in plant cell walls

Hydrogen bond

a relatively weak bond formed by the attraction between a group with a small positive charge on a hydrogen atom (Hδ+) and another group carrying a small negative charge (δ−), e.g. between two -Oδ- Hδ+ groups

Ester bond/ ester linkage

a chemical bond, represented as -COO- , formed when an acid reacts with an alcohol

Triglyceride

a type of lipid formed when three fatty acid molecules combine with glycerol, an alcohol with three hydroxyl (−OH) groups

Peptide bond

the covalent bond joining neighbouring amino acids together in proteins; it is a C-N link between two amino acid molecules, formed by a condensation reaction

Polypeptide

a long chain of amino acids formed by condensation reactions between the individual amino acids; proteins are made of one or more polypeptide chains; see peptide bond

primary structure of protein

the sequence of amino acids in a polypeptide or protein

secondary structure of protein

the structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (an α-helix or β-pleated sheet)

α-helix

a helical structure formed by a polypeptide chain, held in place by hydrogen bonds; an α-helix is an example of secondary structure in a protein

β-pleated sheet

a loose, sheet-like structure formed by hydrogen bonding between parallel polypeptide chains; a β-pleated sheet is an example of secondary structure in a protein

tertiary structure of protein

the compact structure of a protein molecule resulting from the three-dimensional coiling of the chain of amino acids

quaternary structure of a protein

the three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule

Haemoglobin

the red pigment found in red blood cells, whose molecules contain four iron atoms within a globular protein made up of four polypeptides; it combines reversibly with oxygen

Globular protein

a protein whose molecules are folded into a relatively spherical shape, often has physiological roles and is often water-soluble and metabolically active, e.g. insulin, haemoglobin and enzymes

Sickle cell anaemia

a genetic disease caused by a faulty gene coding for haemoglobin, in which haemoglobin tends to precipitate when oxygen concentrations are low

Collagen

the main structural protein of animals; known as 'white fibres', the fundamental unit of the fibre consists of three helical polypeptide chains wound around each other, forming a 'triple helix' with high tensile strength

Fibrous protein

a protein whose molecules have a relatively long, thin structure that is generally insoluble and metabolically inactive, and whose function is usually structural, e.g. keratin and collagen

Biuret test

a test for the presence of amine groups and thus for the presence of protein; biuret reagent is added to the unknown substance, and a change from pale blue to purple indicates the presence of protein