2. Definition
◦ Lipids are water-insoluble biomolecules that have
high solubility in organic solvents
◦ Lipid compounds includes monoglycerides,
diglycerides, triglycerides, phospholipids, sterols,
fatty acids etc
3. Biological roles of lipids
◦ Source of energy
◦ Carrying fat soluble vitamins (A, D, E, K)
◦ Structural components of brain, cell membranes
and other tissues
◦ Source of various bioactive compounds and
antioxidants
4. Fatty acids consist of elements C, H and O
arranged as a carbon chain skeleton with a
carboxyl group at one end
These molecules are amphipathic
Can be grouped into saturated and
unsaturated FA
5. Saturated fatty acids have all the hydrogen
that the carbon atoms can hold, ie no double
bonds
Unsaturated fatty acids have double bonds in
the hydrocarbon backbone
6.
7. Monounsaturated fatty acids have one double
bond
Polyunsaturated fatty acids have more than
one double bond
8. The systematic name of fatty acids are
derived from the name of its parent
hydrocarbon by substitution of oic for the
final e
Examples are:
Butane(4C) – Butanoic acid
Hexadecane (16C) – Hexadecanoic acid
9. By convention the carbon of the carboxyl
group is carbon number one
Greek numeric such as di, tri, tetra, penta,
hexa are used to describe the number of
carbon
Common names are often used more than the
systematic names
10. Carbon number 2 is known as alpha(α)
carbon and the last carbon in the series is
known as omega(ω) carbon
The double bond is indicated by ∆ followed
by the number of carbon as superscript
◦ Eg ∆2 means a double bond between carbon 2 and
three, ∆9 means a double bond between carbon 9
and 10
11. The orientation of hydrogen atoms on the
double bond can be Cis or Trans
Cis means on the same side and trans means
across or on the other side
12. Most fatty acids occurring in nature are in cis
form, the trans form results from chemical
hyrogenation of polyunsaturated FA in
vegetable oils
13. The double bonds binds carbon atoms tightly
and prevent the rotation of carbon atoms
along the bond axis
Fatty acids can be represented by showing
the number of carbons and the number of
double bonds eg 18:1, 18:2, 18:3
14. 14:0, Myristic acid, CH3(CH2)12COOH, often
found attached to the N-term. of plasma
membrane
16:0, Palmitic acid, CH3(CH2)14COOH, End
product of mammalian fatty acid synthesis
16:1∆9, Palmitoleic acid,
CH3(CH2)5C=C(CH2)7COOH
18:0, Stearic acid, CH3(CH2)16COOH
16. These are unsaturated essential fatty acids
that need to be incorporated into diet
because the human metabolism can not
create them
Omega 3 are acids with the double bond at
3C away from omega carbon and in omega 6
the double bond is 6C from omega carbon
17. Linolenic acid is an omega 3 FA
(18:3∆9,12,15)
Arachidonic acid is omega 6 FA
(20:4∆5,8,11,14)
They are essential fatty acids, are supplied by
dietary plant oils
EFA are precursors for eicosapentanoic acid
(EPA) and docosahexanoic acid (DHA)
EPA and DHA are found in fish oils, are used
for synthesis of eicosanoids
18. Are main constituents of vegetable oils and
animal fats
At room temperatures may be solid or liquid,
when liquid are called oils and when solid
they are called fats
Acylglycerols contain glycerol and FA
A TAG is formed from one molecule of
glycerol and 3 molecules of FAs
19.
20. TAGs are:
◦ Non polar
◦ Hydrophobic
◦ Insoluble in water
◦ This is due to utilization of the polar groups of
glycerol and fatty acids
21. Specialized cells in animal cells eg adipocytes
stores large amounts of TAGs as fat droplets
Also TAGs are stored in many plant seeds and
serves as a source of energy during
germination
22. TAGs are good source of energy bcs
◦ Yields more energy than CHO (more than twice)
◦ Are hydrophobic, unhydrated, therefore the body
does not carry extra molecules of water
23. Heating TAGs with alkaline solutions eg.
NaOH or KOH yields glycerol and salts of fatty
acids
This is the reaction which is used for
manufacturing soaps
Soaps are useful because can solubilize
water-insoluble materials by formation of
miscelles
24. Consist of alcohol such as glycerol, one or
two molecules of fatty acids and a phosphoric
acid compound
They are natural surfactants and emulsifiers
They are found in all animals and plant cells
25.
26. X can be:
◦ Ethanolamine
◦ Choline
◦ Serine
◦ Glycerol
◦ Inositol
◦ Phosphatidyl glycerol
27. The most common phospholipids are:
◦ lecithin (phospatidylcholine)
◦ Phosphatidylethanolamine
◦ Phosphatidylinositol and
◦ Phosphatidylserine
29. Lecithin is a significant constituent of brain
and nervous tissue
Cell walls and other biological membranes
consist of two layers of phospholipids
Fatty acid tails of the phospholipids are
oriented toward each other and the
phosphate groups form the outer surfaces of
the membrane
