Unit 3 Chemistry – large Biomolecule #1 – Lipids


lipids are fats, oils, waxes or steroids, non-polar, insoluble organic compounds
in our diet, lipids supply and store energy [37 kJg-1] as well as a protective layer
around organs
Formation of Fats and Oils

molecules in fats and oils are formed by a condensation reaction between a glycerol
[a tri-alkanol] molecule and 3 molecules of a fatty acid [high Mr carboxylic acid] …
glycerol
stearic acid CH3(CH2)16COOH
+
+
+
condensation reaction [esterification]
H2C-O-CO-(CH2)16CH3
l
HC-O-CO-(CH2)16CH3 + 3 H2O
ester linkage
l
water molecules produced
H2C-O-CO-(CH2)16CH3
tristearin – a triglyceride ester
[ molecule in fat ]


the condensation reaction [producing water molecules] is also an ester forming
reaction, the tristearin being a triglyceride ester formed between glycerol [a trialkanol] and carboxylic acid [fatty acid].
in the body, this condensation reaction is enzyme controlled

the
–O-Cll
O
is an “ester linkage” or ester functional group
Types of Fat


fats can be classified according to the fatty acids from which they are made
saturated fats are made from fatty acids having only single C-C bonds ..
eg. CH3(CH2)14COOH palmitic acid

mono-unsaturated fats are made from fatty acids having one C=C double bond
eg. CH3(CH2)7CH=CH(CH2)7COOH oleic acid

polyunsaturated fats are made from fatty acids having >1 C=C double bond
eg. CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH linoleic acid

saturated fats have a higher melting point, are more waxy and cause cardiovascular
problems; unsaturated fats tend to be flowing oils
animal fats tend to have a higher proportion of saturated fat than vegetable sources

Reactions of Fats in the Body
1.



Condensation
enzyme catalysed esterification between glycerol and fatty acid
reaction in aqueous solution [assisted by emulsifiers]
occurs when excess fatty acids in body are converted into fat in adipose tissue
OH
O-CO-R
OH + 3 R-COOH(aq)
fatty acid
OH
glycerol
2.



O-CO-R + 3H2O(l)
water
O-CO-R
triglyceride
ester
Hydrolysis
enzyme catalysed hydrolysis [reaction with water] of lipid molecule
hydrolysis is the reverse reaction of the condensation reaction
occurs during digestion of fats in the body
O-CO-R
O-CO-R
O-CO-R
OH
+ 3H2O(l)
OH + 3 R-COOH(aq)
OH
3. Oxidation
 enzyme controlled exothermic redox reaction of fatty acid and oxygen
CH3(CH2)14COOH(aq) + 23O2(g)  16CO2(g) + 16H2O(l)