Biochemistry Lecture No. 10: Lipids
Thursday September 27 , 2012h
-A lipid is a biological molecule that is not very soluble in water (practically insoluble means
hydrophobic). An example of a practical application of lipids in the body is the lipid bi-layer of which all
cell membranes are comprised.
Saturated & Unsaturated Fatty Acids:
-Saturated fatty acids are saturated with hydrogen atoms. Monounsaturated fatty acids contain 1
element of unsaturation (1 double bond).There are 2 ways you can make unsaturated fats: as a trans or
cis stereoisomer. The difference between the two is in the orientation of the substituents (hydrogen
atoms) as there can be no rotation about the double bond.
-The cis stereoisomer causes fatty acids to form a kink (bend in its shape). Double bonds in biological
systems will tend to put bonds in specific places (between carbons 9 and 10). Cis double bond
arrangements are the norm; trans double bond arrangements are rare in nature (synthetic). When 2 or
more double bonds are present in a fatty acid it is considered a polyunsaturated fatty acid. You normally
don’t get conjugated double bonds ALL CIS
Biochemical Conventions For Fatty Acids:
-C16:1 cis-Δ9 C16:1 (n-7) C16:1 (ω-7) C16:1
-Where C16 is the number of carbons, 1 is the number of double bonds, cis-∆9 is a cis double bond
starting at the 9 carbon form the carboxyl group, (n-7) is the 7 carbon from the end of the fatty acid
chain, (ω-7) is the 7 carbon from the other end of the molecule, and C16:1 assumes that the double
bond is cis and between the 9 and 10 carbon in the fatty acid chain.
-Fatty acid chains usually range from 2 carbons(acetate) to 24 or 30 carbons in saturated fatty acids.
They always have an even number of carbons (around 12 to 20 on average).
Fatty Acid Saturation & Cholesterol:
-Cholesterol in the body comes in two distinct forms: LDL cholesterol (a low-density lipoprotein, carries
cholesterol to tissues) and HDL cholesterol (a high-density lipoprotein, scavenges cholesterol from
tissues). The effect of saturated fats on LDL and HD