1. What is Lipid
Lipids: insoluble in water, but soluble in organic solvents including diethyl ether, chloroform, methylene chloride, and acetone
Amphipathic: hydrophobic in nature
Lipids include:
Open Chain forms
fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids,
lipid-soluble vitamins
prostaglandins, leukotrienes, and thromboxanes
Cyclic forms
cholesterol, steroid hormones, and bile acids

2. Lipid: Structure Open chain: Cyclic forms/Fused ring:
long nonpolar tail with a polar head
Saponifiable
Cyclic forms/Fused ring:
- based on the steroid ring
skeleton

3. LIPID: CLASSESS Fatty acids and their derivatives Triacylglycerols
Phosphoacylglycerol, phosphoglycerides
Sphingolipids
Wax esters
Isoprenoids (based on isoprene structure)

4. LIPID: Structural features
/ phosphoacylglycerol
GENERAL STRUCTURE
The structural features of storage and membrane lipids. (a) The storage lipids are composed of nonpolar triacylglycerol. (b) The membrane lipids are composed of glycerophospholipids and sphingolipids which have polar and nonpolar regions

5. Fatty Acids Nonpolar hydrophobic tail Polar hydrophilic head
Fatty acid: a molecule with a carboxyl group as the polar end and a hydrocarbon chain as the hydrophobic/nonpolar end.
an unbranched-chain carboxylic acid, mostly in even numbers of carbon
Nonpolar hydrophobic tail
Polar hydrophilic head

6. Fatty Acids Nonpolar hydrophobic tail Polar hydrophilic head
derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes
Amphiphatic
Nonpolar hydrophobic tail
Polar hydrophilic head

7. Fatty Acids
Length of fatty acid plays a role in its chemical character
• Usually contain even numbers of carbons (can contain odd, depending on how they are biosynthesized)
• FA - C=C bonds, are unsaturated fatty acid
- C-C bonds, are saturated fatty acid

8. Fatty Acids

9. Fatty Acids
Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point

10. Fatty Acids
In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare
16:19
Palmitoleic acid
Cis double bond results
in a bent chain and lower mp.

11. Fatty Acids
Palmitoleic 16:19 – degree of unsaturation or abbreviation symbol
CH3(CH2)5CH=CH (CH2)7COOH – chemical formula 7 9 5 3 1 11 13 15
Palmitoleic acid

12. Fatty Acids
Oleic acid
18:19
Stearic acid
18:0
structure

13. Fatty Acids

14. CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH CH3(CH2)3(CH2CH=CH)4(CH2)3 COOH
Fatty Acids - examples
Stearic 18: CH3(CH2)16COOH
Oleic acid 18:19 / 18:19 / 18:1- 9
CH3(CH2)4CH2CH2CH2CH=CH(CH2)7COOH
Palmitoleic 16:19
CH3(CH2)5CH=CH (CH2)7COOH
Linolenic 18:29,12
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Arachidonic 20:45,8,11,14
CH3(CH2)3(CH2CH=CH)4(CH2)3 COOH

15. Triacylglycerols Glycerol part Fatty acid chains
Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids
Nonpolar class of lipid, very hydrophobic
Glycerol
part
Fatty acid
chains

16. Triacylglycerols (TAGs)
TAGs which are solids at room temperature are rich in saturated acids and are called fats.
TAGs which are liquids at room temperature are rich in unsaturated acids and are called oils.
e.g. oil seeds include peanut, corn, safflower, palm, olive and soybean.

17. Triacylglycerols (TAGs)
Hydrolysis of TAGs will produce 1 glycerol and 3 fatty acids.
Biologically this is done by lipases.
Chemically base hydrolysis is called saponification.

18. Hydrolysis of Triacylglycerols (TAGs)

19. Saponification
Saponification – reactions of triacylglycerol with … to produce … , which is the sodium salt

20. Phosphoacylglycerols (Phospholipids)
Phosphatidic acid
When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, phosphatidic acid produced
Phosphatidyl ester = phosphoacylglycerol
1 glycerol bonded to 2 fatty acids + phosphate group

21. Phosphoacylglycerols = glycerophospholipids
Phosphoacylglycerols – amphiphatic, polar, hydrophilic
The second most abundant group of naturally occurring
lipids, and they are found in plant and animal membranes
second alcohol

22. Phosphatidyl esters = phosphoacylglycerol = glycerophospholipids
Fatty acid

23. Functions of phospholipids:as
participate in the transduction of biological signals across the membrane
play an important role in the
important source of acetylcholine (common neurotransmitter substance occur in mammals)

24. Phospholipids
glycerophospholipids & sphingolipids have a polar head & 2 hydrophobic tails
Extra space taken by the non-polar tails, these lipids unable to assemble into micelles
So, bilayer is form - nonpolar side combines by hydrophobic interactions to exclude water in the centre region of bilayer
Salts of fatty acid with polar head and a single nonpolar assemble into spherical structures - micelles

25. Sphingolipids No glycerol
Contain sphingosine, a long-chain amino alcohol
Found in
Abundant in nervous system
Bares structural similarity to phospholipids

26. Sphingolipids (simplest)
Primary alcohol group esterified to phosphoric acid which esterified to choline

27. Sphingolipids + sugar residue = Glycolipids
glycosphingolipid
Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid
In most cases, sugar is either glucose or galactose
many glycolipids are derived from ceramides
Glycolipids with complex carbohydrate moiety that contains more than 3 sugars are known as gangliosides

28. Ganglioside
Most complex glycosphingolipid

29. Waxes
A complex mixture of esters of long -chain carboxylic acids (fatty acids) and alcohols
Found as protective coatings for plants and animals

30. Steroids
Steroids: a group of lipids that have fused-ring structure of 3 six-membered rings, and 1 five-membered ring.
Most abundant steroid:cholesterol
E.g.: vit D, estrogen, cortisone

31. Cholesterol
The steroid of most interest in our discussion of biological membranes is cholesterol
Amphiphilic –
but more hydrophobic than
glycerophospholipids
and sphingolipids

33. Phytosterol
Plant steroid

34. Vitamins E, K, -carotene
Isoprenoids
Based on isoprene structures
Vitamins E, K, -carotene

35. Example
isoprene

36. Eicosanoids Eicosanoids
a family of compounds that have the 20-carbon skeleton
Arachidonic acid as precursor
Example: prostaglandins and leukotrienes

37. Lipid soluble vitamins

38. Lipid: Functions Storage molecules for energy Membrane components
Messenger
Mediate the hormonal responseand synthesis of hormones

39. Fluid-mosaic model