Summary OCR A/AS-Level Biology 2.2.6 Biochemistry of Lipids

Biochemistry of Lipids
Lipids
 Macromolecules not polymers – different components joined together
 Non-polar so insoluble on water and don’t affect water potential
 3 important types:
Triglycerides Phospholipids Steroids

Functions of Lipids
 Energy source – broken down into ATP during respiration
 Energy storage – adipose cells store fat which doesn’t dissolve in water
 Insulation – adipose tissue reduces heat loss
 All biological membranes are made up of lipids
 Protection – surface of plant leaves and delicate animal organs
 Buoyancy – fat is less dense than water
 Some hormones are lipids such as steroids

Glycerol
 3 carbon (C) atoms and 3 hydroxyl (-OH) groups
 Free hydroxyl group makes it an alcohol

Fatty Acids
 Carboxyl group (-COOH) at one end attached to a hydro-carbon tail made of only
hydrogen and carbon
 Anything from 2-20 carbons long (usually even)
 Carboxyl group ionises into H+ and COO-
 Is an acid since it produces a free H+ ion
 Can be saturated (no double carbon bonds), monounsaturated (1 double carbon bond)
or polyunsaturated (2 or more double carbon bonds)
 Double bonds make the chain kink so the lipids cannot stack and instead become fluid
making them oils not fats
 More C=C bonds means less hydrogen atoms, more fluidity and a lower melting point
 More unsaturated fats give a lower melting point

Triglycerides
 Glycerol + 3 fatty acids bonded by ester bonds
 Many different fatty acids
 Many are made in our bodies, some must be ingested
 Stored as fat, which has insulative, buoyant and protective properties