The Fats of Life Dr Hilary MacQueen Denbigh School November 2010
Apr 01, 2015
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!