Cambridge AS level Biology Notes: Lipids explained by an A* student

LIPIDS
FATTY ACIDS ALCOHOLS AND ESTERS TRIGLYCERIDES

Contains the group -COOH Contains a -OH group (hydroxyl) attached The most common lipids
(carboxyl) to a carbon atom
Also called “fats and oils”
Large molecules have long Glycerol: 3 -OH groups
Insoluble in water/ hydrophobic
hydrocarbon tails attached to the
head ACID + ALCOHOL = ESTER Soluble in organic solvents (ether)

Unsaturated fatty acids:

• Contain double bonds(-
C=C-)
• Contains a lower amount
of hydrogen
• Form unsaturated lipids

Contains 1 double bond:

Monounsaturated fat

Contains more than 1 double
bond:

Polyunsaturated fat

Eg: Oil, plant lipids

Saturated fatty acids:
ROLES:
• Doesn’t have double
bonds • Acts as an energy reserve
• Because they have more
Eg: Animal lipids C-H bonds than
carbohydrates
• Acts as an insulator
against heat loss
• Acts as a metabolic
source of water (during
respiration)
• Acts as phospholipids

PHOSPHOLIPIDS
• One of the 3 fatty acid
molecules is replaced by
a phosphate group
• Phosphate head:
hydrophilic
• 2 fatty acid tails:
hydrophobic