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Learning outcomes:(a) Describe the structures, properties and

distribution of triglycerides(b) State the functions of triglycerides, phospholipids

and steroids(c) Differentiate between saturated and unsaturated

fatty acids

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Organic compounds, contain a high

proportion ofCH2- (hydrocarbon) groups. Some lipids may contain P and N.

Hydrophobic organic compounds, insolublein water but dissolve in organic solvents /non-polar organic solvents such as acetone,benzene and petroleum ether.

They are esters formed from fatty acid andalcohol.

3 main groups : triglycerides, phospholipidsand steroids.

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Condensation of one molecule ofglycerol and3 molecules offatty acid to form an ester.

This formation is known as esterification.

Saturated fatty acid (eg. Stearic acid,C17H35COOH) : a fatty acid with itshydrocarbon chain having the maximumnumber of hydrogen atoms bound to it.

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Glycerol three carbon skeleton hydroxyl group attached to each.

A fatty acid a carboxyl group attached to a long

carbon skeleton, 16 to 18 carbons long.

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Many nonpolar C-H bonds in the longhydrocarbon skeleton make fats hydrophobic. In a fat,

three fatty acids are joined to glycerol by an ester linkage creating a triglyceride

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Saturated fatty acid Unsaturated fatty acid

single C C bonds

More H : C ratio usually solid at room

temperature

Less reactive

is called fatFound more in animals

example : Stearic acid,

C17H35COOH

one or more double

- C = C - bonds

monounsaturated ( a

double bond) or

polyunsaturated (two or

more double bonds)

Less H : C ratio usually liquid at room

temperature

Easier to metabolise

is called oilFound more in plants

example : Oleic acid,

C17H33COOH, Palmitic acid,

C15H31COOH

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Essential fatty acid Non-essential fatty acid

Example : linoleic acid,

linolenic acid & arachidonicacid.

unsaturated fatty acids

Necessary for the

formation of phospholipids cannot be synthesised by

our body, must be obtained

from daily diet.

our body is able to

syhthesise duringmetabolic activities

involving carbohydrates

and proteins

not necessary to obtainthrough our diet

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Act as energy sources Act as insulator. Animals store extra fat

below the dermis of the skin to keep theirbodies from cold

Act as energy reserves in the adipose tissueof animals and seeds of many plants

Can be used for the formation of otherchemicals including glucose and amino acids

Protect organs such as the kidney fromphysical damage

Make animals and plants waterproof

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A derivative of triglyceride. One molecule of fatty

acid chains is replaced by phosphoric acidbecomes hydrophilic because phosphate is acharged ion (hydrophilic head).

Another 2 hydrocarbon chains still remain

hydrophobic (hydrophobic tail) Hence, phospholipid is said to be amphipathic. Example : lecithin (phosphotidylcholine) has a

+ve charged choline group bound to thephosphate group. An important component of thecell membrane and membrane of organelles.

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The interaction of phospholipids with water iscomplex. The fatty acid tails are hydrophobic. The phosphate

group and its attachments form a hydrophilic head.

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When phospholipids are added to water, self-assemble into aggregates with the hydrophobic tails pointing toward thecenter and the hydrophilic heads on the outside.

This type of structure is called a micelle.

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At the surface of a cell , phospholipids are arranged asa bilayer. Again, the hydrophilic heads are on the outside in

contact with the aqueous solution and thehydrophobic tails from the core. The phospholipid bilayer forms a barrier betweenthe cell and the external environment.

They are the major component of membranes.

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Main component and forms the basic structure ofthe membrane with hydrophilic heads facingoutside, hydrophobic tails opposite each other.

forms the bimolecular layer in the membrane. The phospholipid molecules in the membrane are

dynamic which means each of the molecules canmove freely or they are fluid-like.

Ensure the stability in the membrane. Permits small molecule to diffuse easily across the

membrane. Acts as a barrier for polar moleculesand ions to cross the membrane.

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Lipids that are made of four fused hydrocarbon

rings. There are 17 carbon atoms within the molecule.

The differences in the side chains give rise todifferent types of steroid.

Steroids are found in both plants and animals. Example : cholesterol, testosterone, oestrogen,

progesterone, adrenocortical hormones, calciferoland bile salts.

Not soluble in water as they are hydrophobic.

Soluble in organic solvents such as petroleum

ether & acetone.

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Sex hormones like testosterone, oestrogen andprogesterone for maintaining sexual health.

steroid hormones from adrenal cortex, forexample, corticoids are required for glucose andmineral metabolism.

Synthesis ofmembrane structure as such it is forthe general well being of the skin cells and body.

Steroid such as bile salts, emulsify lipids in ourfood in the small intestine.

Steroids form vitamin D in the skin is needed forthe metabolism of calcium and phosphate.

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As an energy source

For energy storage Provides structural support

As heat and electrical insulator

To protect internal organs

As a waterproof substance

As a precursor of other steroids

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