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Lipids are a diverse collection of substances that have a range of different functions in living systems

Lipids are compounds that serve both as structural and nutrient substances

The lipid group includes fats and oils, waxes, steroidsand phospholipids. These molecules have a low solubility in water

but a high solubility in solvents such as ethanol and chloroform

Fats & oils are formed from molecules of glycerol

and fatty acids

The Nature of LipidsThe Nature of Lipids

GlycerolMethylgroup

Carboxylicacid group

A Fatty Acid

Hydrocarbonchain

Glycerol is a 3-carbon alcohol molecule

Fatty acids are composed of hydrocarbon chains ofvarying length with a methyl group at one end and a

carboxylic acid group at the other

The Components of Fats & Oils The Components of Fats & Oils

Double bond

Unsaturated fatty acid:less saturated with

hydrogen atoms

32 3

Saturated fatty acid

General formula for asaturated fatty acid

2 n 3

Saturated & Unsaturated Fatty AcidsSaturated & Unsaturated Fatty Acids

ATRIGLYCERIDE

-3H2O Condensation Reaction

Ester bond

GLYCEROLTHREE

FATTY ACIDMOLECULES

Formation of a TriglycerideFormation of a Triglyceride

OR

hydrophilic phosphategroup

Gl y

cero

l

Fatty acid

Fatty acid

Phosphate

hydrophobic tails

Gl y

cer o

l

Fatty acid

Fatty acid

Phosphate

PhospholipidsPhospholipids

Polar phosphate head(hydrophilic)

Hydrophobic fatty acid(lipid) tails

The phosphate-containing endof the phospholipid molecule is

soluble in water, while thehydrophobic fatty acid tails

orientate themselves in positionsaway from a watery medium

The bipolar nature ofphospholipids allows these

molecules to form bilayers thatform a major component

of cell membranes

PhospholipidsPhospholipids

PHOSPHOLIPIDBILAYER

water

water

phospholipidbilayer of cellmembrane

cholesterol stabilisingthe membrane

Cholesterol moleculesare located between thetails of the phospholipidmolecules where they serve to stabilise the

membrane

These cholesterol moleculesare also classed as LIPIDS

although they belong toa very different sub-group

known as STEROIDS

Fats & oils are made up of carbon, hydrogen and oxygen atoms.

The building blocks (monomers) of fats and oils are glycerol & fatty acid molecules.

Fats & oils are TRIGLYCERIDES. Three fatty acid molecules bond to each glycerol

molecule by CONDENSATION REACTIONS. The bonds formed from these condensation reactions

are called ESTER BONDS. Fats & oils are chemically similar but physically

different. Fats are solid at room temperature whereas oils are

liquid.

SummarySummary

Monoglycerides & diglycerides also form when glycerol and fatty acids bond by condensation reactions.

Monoglycerides form when only ONE FATTY ACID bonds with a glycerol molecule.

Diglycerides form when TWO FATTY ACIDS bond with a glycerol molecule.

Phospholipids are DIGLYCERIDES. Phospholipids form when TWO FATTY ACIDS and a

PHOSPHATE group bond to a glycerol molecule. The phosphate end of the molecule is hydrophilic

(water-loving) and the two fatty acids tails are hydrophobic (water-hating).

Phospholipids are a major structural component of cell membranes.

Steroids such as cholesterol, oestrogen and progesterone also belong to the class lipids.