Biological molecules

Learning objectives

Describe and carry out the Benedict's, iodine, emulsion and biuret tests, the acid-hydrolysis test for non-reducing sugars such as sucrose, and a standardised semi-quantitative Benedict's test that estimates sugar concentration from colour standards or the time to the first colour change.

Draw α-glucose and β-glucose as rings, showing how the position of the OH group on carbon 1 differs, use the terms monomer, polymer, macromolecule, monosaccharide, disaccharide and polysaccharide, and describe how condensation forms and hydrolysis breaks glycosidic bonds, naming glucose, fructose and maltose as reducing sugars and sucrose as non-reducing.

Relate the structures of amylose, amylopectin, glycogen (1,4 and 1,6 glycosidic bonds, coiling, branching) and cellulose (straight β-glucose chains hydrogen-bonded into microfibrils) to energy storage and to the strength of plant cell walls.

Describe triglycerides as non-polar molecules of glycerol and three saturated or unsaturated fatty acids joined by ester bonds, relate their structure to energy storage, insulation and buoyancy, and describe phospholipids with hydrophilic phosphate heads and hydrophobic fatty acid tails.

Describe amino acid structure, peptide-bond formation and hydrolysis, the four levels of protein structure and the hydrophobic, hydrogen, ionic and disulfide bonds that hold them, and relate globular haemoglobin (two α-globin and two β-globin chains with iron-containing haem) and fibrous collagen (triple helices cross-linked into fibres) to their functions.

Explain how hydrogen bonding between polar water molecules gives water its solvent action, high specific heat capacity and high latent heat of vaporisation, and why each property matters to living organisms.