1.14 Triglycerides, saturated and unsaturated fatty acids

Describe and explain the properties of lipids

• macromolecules that contain carbon, hydrogen and oxygen —→ yet contain a much lower proportion of oxygen than carbohydrates, yet contain more carbon and hydrogen, hence they can store more energy per gram - hence, lipids are a more compact way of storing energy

• non-polar and hydrophobic —→ insoluble in water

• composed of fatty acids and glycerol

State and explain the function of lipids

• cellular structure - phospholipids needed for the flexibility of cell membranes

• energy storage - fat around major organs and fat under the skin

• insulation - stored under the skin for warmth in mammals / around nerve axons e.g myelin sheath

• protection - fat stored around delicate organs which acts as a shock absorber

• hormone production - oestrogen in girls

Describe, draw and label the formation of trigylcerides

• glycerol and fatty acids join together by forming 3 ester bonds (ester bond is between a hydroxyl group (-OH) on a glycerol molecule and a carboxyl group (-COOH) on a fatty acid

• this is through a condensation reaction called esterification

• 3 water molecules are produced when the triglyceride forms

simple equation:

glucerol + 3 fatty acids —→ triglyceride + 3H₂ O

Describe and draw the structure of a saturated fatty acid

• contain no carbon-carbon double bonds

• the hydrocarbon chain is saturated with hydrogen atoms due to the absence of double bonds

• they form unbranched, linear / straight chains

• hence pack closely together

• stronger intermolecular forces—→ have higher melting points = solids at room temperature

e.g butter

Describe and draw the structure of an unsaturated fatty acid

• monounsaturated : have one carbon to carbon double bond

• polyunsaturated : has more than one double carbon to carbon bond

• lower hydrogen to carbon ratio

• the double carbon to carbon bonds form kinks - the chains are not straight and so cannot pack closely together

• has weaker intermolecular forces —→ liquid at room temperature

e.g oils

Compare the structures of saturated fatty acids and unsaturated fatty acids

• 
  both have a hydrocarbon chain

• both are formed from one glycerol and three fatty acids

• both have a -COOH group at one end

• in both the glycerol and fatty acids are held together by an ester bond

• saturated has a higher ratio of H:C atoms than unsaturated

• saturated has no double crabon to carbon bonds whereas unsaturated does

• saturated forms straught chains so can pack closely together whereas unsaturated cannot as they form kinks