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

Lipid: Structure

1. Open chain:– long nonpolar tail with a polar head– Saponifiable

2. Cyclic forms/Fused ring:- based on the steroid ring skeleton

OH

Oeg. A fatty acid

A B

C D

LIPID: CLASSESS

1. Fatty acids and their derivatives2. Triacylglycerols3. Phosphoacylglycerol, phosphoglycerides 4. Sphingolipids 5. Wax esters6. Isoprenoids (based on isoprene structure)

LIPID: Structural features

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

GENERAL STRUCTURE

/ phosphoacylglycerol

Fatty Acids

• 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

Fatty Acids

• derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes

• Amphiphatic

Nonpolar hydrophobic tail

Polar hydrophilic head

• 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

Fatty Acids

Fatty Acids

Fatty Acids

• Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point

Fatty Acids• In most unsaturated fatty acids, the cis isomer

predominates; the trans isomer is rare

Cis double bond results in a bent chain and lower mp.

Palmitoleic acid

16:19

Fatty AcidsPalmitoleic 16:19 – degree of unsaturation or abbreviation symbol

CH3(CH2)5CH=CH (CH2)7COOH – chemical formula

Palmitoleic acid

13579

11

13

15

Fatty Acids

Stearic acid

18:0

Oleic acid

18:19

structure

Fatty Acids

Fatty Acids - examples1. Stearic 18:0 CH3(CH2)16COOH

2. Oleic acid 18:19 / 18:19 / 18:1- 9

CH3(CH2)4CH2CH2CH2CH=CH(CH2)7COOH

3. Palmitoleic 16:19

CH3(CH2)5CH=CH (CH2)7COOH

4. Linolenic 18:29,12

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

5. Arachidonic 20:45,8,11,14

CH3(CH2)3(CH2CH=CH)4(CH2)3 COOH

Triacylglycerols• Triacylglycerol (triglyceride): an ester of glycerol

with three fatty acids• Nonpolar class of lipid, very hydrophobic

Glycerolpart

CH2

CH

CH2

O

O

O CO

CO

CO

R1

R2

R3

Fatty acid chains

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.

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.

Hydrolysis of Triacylglycerols (TAGs)

Saponification

CH2

CH

CH2

O

O

O CO

CO

CO

R3

R3

R3

3 NaOH

CH2

CH

CH2

OH

OH

OH

+

NaO CO

R3a soap, Na or Ksalt of a fatty acid

3

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

Phosphoacylglycerols (Phospholipids)

• When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, phosphatidic acid produced

• Phosphatidyl ester = phosphoacylglycerol

CH2

CH

CH2

O

O

O PO

CO

CO

R1

R2

OH

O

Phosphatidic acid

1 glycerol bonded to 2 fatty acids + phosphate

group

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

Phospholipids

Phosphatidyl esters = phosphoacylglycerol = glycerophospholipids

CH2

CH

CH2

O

O

O PO

CO

CO

R1

R2

OR

O

R=

CH2CH2NH3

+

phosphatidylethanolamine

CH2CH2N(CH3)3+

phosphatidylcholine(lecithin)

CH2CHOH

CH2O PO

OO CH

CH2

OOCO

CO

R3R4

diphosphatidylglycerol(cardiolipin)

Fatty acid

• Functions of phospholipids: as participate in the transduction of biological

signals across the membrane as play an important role in the important source of acetylcholine (common

neurotransmitter substance occur in mammals)

Salts of fatty acid with polar head and a single nonpolar assemble into spherical structures - micelles

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

Phospholipids

Sphingolipids

• No glycerol• Contain sphingosine, a

long-chain amino alcohol• Found in

• Abundant in nervous system

• Bares structural similarity to phospholipids

Sphingolipids

(simplest)

Primary alcohol group esterified to phosphoric acid which esterified to choline

Sphingolipids + sugar residue = Glycolipids

• 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

glycosphingolipid

Ganglioside

Most complex glycosphingolipid

Waxes• A complex mixture of esters of long -

chain carboxylic acids (fatty acids) and alcohols

• Found as protective coatings for plants and animals

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

Cholesterol• The steroid of most interest in our discussion of

biological membranes is cholesterol• Amphiphilic –

but more hydrophobic thanglycerophospholipidsand sphingolipids

O

CH3

CH3

OH

testosterone O

CH3

CH3

C

CH3

O

progesterone

Phytosterol• Plant steroid

Isoprenoids• Based on isoprene structures

Vitamins E, K, -carotene

Exampleisoprene

Eicosanoids

• a family of compounds that have the 20-carbon skeleton

• Arachidonic acid as precursor• Example: prostaglandins and leukotrienes

Eicosanoids

Lipid soluble vitamins

1. Storage molecules for energy

2. Membrane components

3. Messenger

4. Mediate the hormonal responseand synthesis of hormones

Lipid: Functions

Fluid-mosaic model