LipidsLipids

The abbreviated structural formula of a

fatty acid is:-

C C CC C

The R group (a hydrocarbon chain)

R COOH

Lipids are a group of compounds that include fats, oils and waxes. They are large molecules and all contain the elements carbon, hydrogen and oxygen.

Two main types of molecules react together when a lipid is formed: glycerol and fatty acids. Complete the diagrams below in your handbook.

Which is often drawn as:-

H

OHH

H

H

H

Glycerol, or

CH2OH

CHOH

CH2OH

R

O

OHC OH

O

RCor

H H

H H

HH

H HHO

O

HC

C

C

OH

OH

(a) Triglycerides form when a condensation reaction joins 3 fatty acid molecules and one molecule of glycerol together. Complete the diagram below to show how the 3 fatty acid molecules would arrange themselves next to the glycerol molecule just before reacting.

C

C

C

H

H

H

H

H

OH

OH

OH

HO

HO

HO C

C

C

O

O

O

R

R

R

3H2O

C

C

C

H

H

H

H

H

O

O

O C

C

C

O

O

O

R

R

R

After the reactions, a triglyceride molecule and 3 water molecules are formed. Complete the diagram below to show this:-

On the same diagram, use a red pen to circle the atoms that will form the 3 water molecules which will be released during the condensation reactions.

You need to know about two types of lipids: Triglycerides and Phospholipids.

This reaction is also known as an esterification in which 3 ester bonds are formed. Highlight and label the 3 ester bonds on your triglyceride diagram above.

+3H2O

The simplified structure of a triglyceride can be shown as a box diagram:-

Gly

cero

l

Fatty Acid

Fatty Acid

Fatty Acid

Put a label in each of the boxes.

A Triglyceride

The properties of different fats depend on the nature of the fatty acids that are linked to it. Make brief notes about the following:-

Saturated Fatty Acids

Unsaturated Fatty Acids

Present in solid fats at room temperature i.e. most animal fats e.g. lard, waxes

Have all single bonds C C in the hydrocarbon chain sections

Present in liquid oils at room temperature i.e. most plant oils e.g. sunflower oil, olive oil, vegetable oil.

Have one or more double bonds C C in the hydrocarbon chain sections

The Functions of Triglycerides

1. Energy Store - When respired triglycerides release 2 x as much energy as an equivalent mass of carbohydrate or protein.

2. Insulation from cold (e.g. fat layer in seals, blubber in whales)

3. Protection for Vital Organs from physical damage (e.g. layer of triglycerides round kidneys)

4. Buoyancy and Waterproofing (e.g. in geese and ducks)

(b) Phospholipids are extremely important in biology because they make up the structure of all cell membranes, including the membranes found on organelles inside cells. A phospholipid molecule has a similar structure to a triglyceride, except that one fatty acid is replaced by a phosphate group. Label the phospholipid box diagram below:

Indicate which end of the phospholipid structure is (i) hydrophilic and (ii) hydrophobic on both of the diagrams above.

Gly

cero

lPhosphate

Group

Fatty Acid

Fatty Acid

A Phospholipid

PO4–

(negatively charged)

A phospholipid molecule can be simplified further to:-

Negatively charged phosphate group

Non-polar 2 fatty acid chains

Hydrophilic end of molecule (‘water-liking’)

Hydrophobic end of molecule (‘water-hating’)

-ve

TASKS

Sketch to show the arrangement a collection of phospholipids makes:

(a) On water surface

(b) Immersed in water

Refs: NT p51 fig 4,

Collins Fig 8b from p12 AS

A Bilayer of

Phospholipids

A Monolayer of

Phospholipids

The formation of phospholipid bilayers is a HUGE ADVANTAGE in cells. This is the basic arrangement of phospholipids in all membranes and it ensures that each different cell type can create it’s own particular internal environment separate to another cell, and ALSO, so that the different organelle types can create their own particular internal environment separate to other organelles.

IMPORTANT NOTE: