the fats of life dr hilary macqueen denbigh school november 2010

The Fats of Life

Dr Hilary MacQueen

Denbigh SchoolNovember 2010

Plan

• Chemistry of fatty acids• Naming fatty acids• Cis and trans fatty acids• Fat in the body• New research

Chemical formulae of fatty acids

Fatty acid nomenclature

• Triacylglycerol = TAG = triglyceride• Saturated = no C—C double bonds• Monounsaturated = one C—C double bond• Polyunsaturated = more than one C—C double bond• N = omega

Fat chemistry

• Three fatty acids attached to one glycerol• Fatty acids are long chains of COOH.(CH2)n.CH3

• The variation lies in the (CH2)n part

• Chains with between 2 and 36 C atoms are common, though some microbes can have up to 80

Double bonds in fatty acids• Fatty acids containing C—C double bonds are

called unsaturated• Double bonds are inserted into fatty acid chains

by desaturase enzymes• The first double bond always goes in between the

8th and 9th C, counting from the COOH end• Extra double bonds are always separated by at

least one single C—C bond• Animals can put in extra double bonds only

between the first one and the COOH end• Plants can also put extra double bonds between

the first and the CH3 end

Double bonds cause the chain to bend

Shape and function of fatty acids

• Saturated fatty acids can pack tightly together– They tend to be more solid at room temperature– Examples are butter, lard, suet, wax

• Unsaturated fatty acids cannot pack so tightly– They tend to be more liquid at room temperature– Examples are margarine, cooking oil, bath oil

How are fatty acids named?

• C18:0 stearic acid

How are fatty acids named?

• C18:0 stearic acid• C18:1 oleic acid

How are fatty acids named?

• C18:0 stearic acid• C18:1 oleic acid• C18:2n-6 linoleic acid

How are fatty acids named?

• C18:0 stearic acid• C18:1 oleic acid• C18:2n-6 linoleic acid• C18:3n-3 -linolenic acid

How are fatty acids named?

• C18:0 stearic acid• C18:1 oleic acid• C18:2n-6 linoleic acid• C18:3n-3 alpha-linolenic acid

essential

Longer-chain fatty acids

• C20:5n-3 eicosapentaenoic EPA• C22:6n-3 docosahexaenoic DHA• C20:4n-6 arachidonic

• Marine fish elongate C18 and have a lot of n-3• Fresh water fish have more n-6

Cis and trans fatty acids

cis

trans

How are fatty acids named?

• C18:0 stearic acid• C18:1 oleic acid• C18:2n-6 linoleic acid• C18:3n-3 alpha-linolenic acid• C18:1t elaidic acid (trans)

Trans fatty acids

• Made by microbes in the rumen• In the cow, most trans fatty acids are oxidised for energy

and about 5% are stored• Hydrogenation also yields trans fatty acids: 90% of oleic

acid is changed into elaidic acid• Trans fatty acids have different physical properties and

taste from the cis versions• Oleic acid is a liquid at room temperature, but elaidic

acid is a solid• Trans fatty acids are less susceptible to spoilage as

enzymes work more slowly on them

Are trans fatty acids harmful?

• We’ve been eating ruminant-derived trans fatty acids for 9000 years

• We eat 2-12 g trans fatty acids per day, ~7% total fat intake

• Diets rich in hydrogenated fats increase this significantly (crisps, fried food, biscuits, pastries, burgers, processed foods)

• Only 5% of the fatty acids in brain membranes are trans, compared to 14% in adipose tissue

• Can trans fatty acids be used fast enough to support function?

Fatty acids and glycerol

CH2-OH HO-CO.(CH2)n.CH3

│CH-OH HO-CO.(CH2)n.CH3

│CH2OH HO-CO.(CH2)n.CH3

CH2-O-CO.(CH2)n.CH3

│CH-O-CO.(CH2)n.CH3

│CH2-O-CO.(CH2)n.CH3

LipolysisEsterification

+ 3H2O

Fatty acids and glycerol

CH2-OH HO-CO.(CH2)n.CH3

│CH-OH HO-CO.(CH2)n.CH3

│CH2OH HO-CO.(CH2)n.CH3

CH2-O-CO.(CH2)n.CH3

│CH-O-CO.(CH2)n.CH3

│CH2-O-CO.(CH2)n.CH3

LipolysisEsterification

+ 3H2O

What do adipocytes look like?

White adipocytes Brown adipocytes

Small mammals

BAT in humans

Changes in BAT

Are women warmer than men?

Are women warmer than men?

Are women warmer than men?

Conclusions

• Fats are essential to our well-being• Fats and oils consist of long C—C chains with varying numbers of

double bonds• We can make some fatty acids, but we need more from our diet• Trans fatty acids are not harmful in moderation• There is a complex fat trafficking system around the body• Fatty acids can be used for making membranes and signalling

molecules• Fat can be used for chemical, mechanical and heat energy• Uncoupling protein keeps you warm!