lipidslipids

What are lipids?What are lipids?

Lipids are a a large and varied group of Lipids are a a large and varied group of organic compounds.organic compounds.

Lipids contain carbon, hydrogen and Lipids contain carbon, hydrogen and oxygen.oxygen.

They are insoluble in water but will They are insoluble in water but will dissolve in organic solvents.dissolve in organic solvents.

There are two types of lipids: fats which There are two types of lipids: fats which are solid at room temp and oils which are are solid at room temp and oils which are liquid at room temp. liquid at room temp.

Triglycerides.Triglycerides.

Triglycerides are made up of a molecule of Triglycerides are made up of a molecule of glycerol join with three fatty acids glycerol join with three fatty acids (RCOOH).(RCOOH).

H HH H

H C OH HOOC.R H-C-OOC.RH C OH HOOC.R H-C-OOC.R

H C OH + HOOC.R H-C-OOC.RH C OH + HOOC.R H-C-OOC.R

H C OH HOOC.R H-C-OOC.RH C OH HOOC.R H-C-OOC.R

H HH H

WATER

Ester bond

Ester bond.Ester bond.

Triglycerides are formed when a glycerol Triglycerides are formed when a glycerol molecule is linked to 3 fatty acid molecule is linked to 3 fatty acid molecules.molecules.

Fatty acids always have –COOH group Fatty acids always have –COOH group (carboxyl group) and this combines with (carboxyl group) and this combines with the –OH group on the glycerol by a the –OH group on the glycerol by a condensation reaction.condensation reaction.

When this happens an ester bond is When this happens an ester bond is formed.formed.

Ester bond

UNSATURATED FATTY ACIDS.UNSATURATED FATTY ACIDS.

Unsaturated fatty acids have double bonds Unsaturated fatty acids have double bonds between some of the carbon atoms.between some of the carbon atoms.

Unsaturated fatty acids have a low melting Unsaturated fatty acids have a low melting point and may be liquid at room point and may be liquid at room temperature.temperature.

Plant oils are an example of an Plant oils are an example of an unsaturated triglyceride that is a liquid at unsaturated triglyceride that is a liquid at room temperature.room temperature.

Structure of a unsaturated fatty Structure of a unsaturated fatty acid.acid.

O H H H H H H H H H H H H H HO H H H H H H H H H H H H H H

C-C-C-C-C-C-C-C=C-C-C-C-C-C-C-HC-C-C-C-C-C-C-C=C-C-C-C-C-C-C-H

HO H H H H H H H H H H H H H H HO H H H H H H H H H H H H H H

In unsaturated fatty acids at least some of In unsaturated fatty acids at least some of the carbon atoms are joined by a double the carbon atoms are joined by a double covalent bond. covalent bond.

Structure of a saturated fat.Structure of a saturated fat.

Saturated fatty acids do not have a double Saturated fatty acids do not have a double bond between the carbon atoms.bond between the carbon atoms.

Saturated fatty acids have a higher melting Saturated fatty acids have a higher melting points and are solid at room temperature.points and are solid at room temperature.

Animal fats are classified as a saturated Animal fats are classified as a saturated fatty acid.fatty acid.

A saturated fatty acid molecule.A saturated fatty acid molecule.

O H H H H H H H H H H H H H H O H H H H H H H H H H H H H H

C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-HC-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H

HO H-H-H-H-H- H-H-H-H-H-H-H-H-HHO H-H-H-H-H- H-H-H-H-H-H-H-H-H

In saturated fats the carbon molecules are In saturated fats the carbon molecules are join together by single covalent bonds.join together by single covalent bonds.

Phospholipids.Phospholipids.

A Phospholipid molecule is like a A Phospholipid molecule is like a triglyceride in which one of the fatty acids triglyceride in which one of the fatty acids have been replaced by a phosphate have been replaced by a phosphate group.group.

The phosphate group gives the The phosphate group gives the phospholipid a hydrophilic head and a phospholipid a hydrophilic head and a hydrophobic tail.hydrophobic tail.

Phospholipids have two ends.Phospholipids have two ends.

A head that contains a phosphate group. A head that contains a phosphate group. This has an uneven charge that makes the This has an uneven charge that makes the head able to mix with water (hydrophilic).head able to mix with water (hydrophilic).

A tail that contains 2 fatty acid chains. A tail that contains 2 fatty acid chains. They have an even charge and this makes They have an even charge and this makes them unable to mix with water them unable to mix with water (hydrophobic).(hydrophobic).

Structure of a phospholipid.Structure of a phospholipid.A phosphate group

Hydrophilic head

Hydrophobic tail

A phospholipid molecule

Test for lipids.Test for lipids.(The emulsion test)(The emulsion test)

Lipids do not dissolve in water, but they Lipids do not dissolve in water, but they will dissolve in ethanol.will dissolve in ethanol.

Add ethanol to the sample being tested.Add ethanol to the sample being tested.Shake the sample and ethanol, so that the Shake the sample and ethanol, so that the

lipids dissolvelipids dissolvePour the mixture of ethanol and sample Pour the mixture of ethanol and sample

into water.into water. If lipids are present the water turns cloudy If lipids are present the water turns cloudy

as a white emulsion is formed.as a white emulsion is formed.