Lipids contain the elements Carbon

Hydrogen Oxygen

There are two main groups:Triglycerides Phospholipids

Triglyceridesone glycerol molecule

3 fatty acids

glycerol

fatty acid

OH

OH

OH

C

C

C

H

H

H

H

H

GlycerolC3H8O3

Fatty Acidscarboxylic acid group (COOH)

joined to a long tail of carbon and hydrogen atomsThe length of the hydrocarbon tail varies,

giving rise to the various fatty acids.

The tail is normally written as R, giving the formula R.COOH

Fatty acids• Organic acids with a carboxyl

(-COOH) group at the end• Joined to the carboxyl group is a

long hydrocarbon tail• This tail differs in each fatty acid• The properties of a lipid depend on

the fatty acids they contain• Fatty acids vary in 2 ways –

•the length of the HC chain •how saturated the molecule is.

COH

OC

H

H

C

H

H

C

H

H

C

H

H

C

H

H

H

Fatty AcidR

R.COOH

COOH

Saturated Fatty Acids

•All bonds between carbon atoms are single

•high melting points•solids at room temperature•associated with animal fats

Unsaturated Fatty Acids

•One or more double bonds between carbon atoms

•low melting points•liquid at room temperature•associated with plant oils

Formation of a triglyceride• Formed as a result of 3 condensation

reactions between glycerol and 3 fatty acids

• involving the –OH group of glycerol and the –COOH group of the fatty acid

• These reactions result in the formation of 3 molecules of water.

• The bond between glycerol and the fatty acid is called an ester bond.

ester bondC

C

C

H

H

H

H

H

OH

OH

OH

R.COOH

R.COOH

R.COOH

glycerol fatty acids

OH

OH

OH

OH

OH

OH

Formation of a triglyceride

HOOC.R

HOOC.R

HOOC.R

condensation

H2O

H2O

H2O

C

C

C

H

H

H

H

H

O

O

O

O

O

O

OC.R

OC.R

OC.R

triglyceride 3 water

PhospholipidsComposed of glycerol, 2 fatty

acids and a phosphate group.

Draw and label diagram p17

Hydrophilic (water loving) head contains glycerol and phosphate group

Hydrophobic (water hating) tail contains 2 fatty acids

• The glycerol and phosphate part is polar and dissolves in water (hydrophilic)

• The fatty acids are non-polar and insoluble (hydrophobic)

• If placed in water the phosphate heads dip into the water and the tails stick out, forming a monolayer

• Draw diagram page 17

Hydrophilic heads

Hydrophobic tails

WATERAIR

When shaken in water phospholipids form hollow ballscalled micelles; the hydrophilic head on the outside

and the hydrophobic tails pointing inside.

Phospholipids are important in cell membranes where they form a phospholipid bilayer; a double layer, heads out, tails in.

Hydrophilic heads

Hydrophilic heads

Hydrophobic tailsPhospholipidbilayer

Functions of lipids• Cell membrane • Energy store• Insulation• Waterproofing/repellent/wax

covering on plant cuticle/exoskeletons

• Buoyancy• Protection• Storage of fat soluble vitamins