LipidsFats and oils

This is a large and diverse group

All lipids contain C, H, O

They are insoluble in water- hydrophobic

Soluble in organic solvents e.g. ethanol

Lipids are the esters formed from fatty acids and alcohol

Joined with an ester linkage which is formed by condensation

Test for lipids – the emulsion test

Lipids are soluble in ethanol

If dissolved in ethanol then added to water a cloudy emulsion will form

The emulsion test

TYPES OF LIPID

It is a broad group which includes -

Fats, oils and waxes

Phospholipids

Complex lipids

Steroids

Structure

Lipids are made of two components

Fatty acids and Glycerol

FATTY ACIDSGeneral formula: RCOOH or

R is H or, usually, a long hydro carbon tail, CH

2CH

2CH

2CH

2 etc

This forms the “tail” in lipids

Tails are Hydrophobic because they are non-polar

COOH is polar (COO- and H+)

Fatty acid tails may be:

Saturated- these melt at higher temperatures,

or

Unsaturated- which melt at lower temperatures, liquid at room temperature

They can be drawn more simply like this

ALCOHOL

Most lipids are esters of glycerol

They are called glycerides

TRIGLYCERIDES3 fatty acids can bond with one glyceride

Each bond is formed by condensation

Ester linkages/bonds are formed

These are ester linkages

R = a long hydrophobic hydrocarbon tail

Lipid structure can be simplified to look like this -

Triglycerides are insoluble in water (non-

polar, hydrophobic)

Soluble in organic solvents

FUNCTIONS:

Used as an energy store (fat): insoluble, compact and high in energy due to large number CH

Buoyancy, warmth, insulation

Release water when oxidised in respiration

NB plants store oils

Phospholipids

These have the same structure as glyceraldehydes but one fatty acid replaced by phosphate.

Phosphate group derived from phosphoric acid.

Bonded with a phosphodiester link

The phosphate group and glycerol form a hydrophilic head

Phospholipids used to make the lipid bilayer in all cell membranes

Structure of a phospholipid

Or more simply: