A-Level Biology – Biological Molecules
(Revision Notes)
1. CARBOHYDRATES
Monosaccharides
Basic carbohydrate units (glucose, galactose, fructose). α-glucose and β-glucose differ at
carbon 1.
Disaccharides
Formed by condensation creating glycosidic bonds. Examples: Maltose (glucose+glucose),
Sucrose (glucose+fructose), Lactose (glucose+galactose). Hydrolysis breaks glycosidic
bonds.
Polysaccharides
Starch = amylose (coiled) + amylopectin (branched). Glycogen = highly branched for quick
glucose release. Cellulose = β-glucose forming strong microfibrils.
2. LIPIDS
Triglycerides
Glycerol + 3 fatty acids (ester bonds). High energy, insoluble, compact.
Phospholipids
Hydrophilic head + hydrophobic tails → form bilayers.
Emulsion Test
Add ethanol, shake, add water. White emulsion = lipid present.
(Revision Notes)
1. CARBOHYDRATES
Monosaccharides
Basic carbohydrate units (glucose, galactose, fructose). α-glucose and β-glucose differ at
carbon 1.
Disaccharides
Formed by condensation creating glycosidic bonds. Examples: Maltose (glucose+glucose),
Sucrose (glucose+fructose), Lactose (glucose+galactose). Hydrolysis breaks glycosidic
bonds.
Polysaccharides
Starch = amylose (coiled) + amylopectin (branched). Glycogen = highly branched for quick
glucose release. Cellulose = β-glucose forming strong microfibrils.
2. LIPIDS
Triglycerides
Glycerol + 3 fatty acids (ester bonds). High energy, insoluble, compact.
Phospholipids
Hydrophilic head + hydrophobic tails → form bilayers.
Emulsion Test
Add ethanol, shake, add water. White emulsion = lipid present.
