LIPIDSLipids are a class of biological molecules defined by low solubility in water and high solubility in nonpolar solvents.

As molecules that are largely hydrocarbon in nature, lipids represent highly reduced forms of carbon and, upon oxidation in metabolism, yield large amounts of energy. Lipids are thus the molecules of choice for metabolic energy storage.

Classification Classification By structure:By structure:1. Simple (fats, oils, waxes, steroids).2. Complex (phospholipids, sphingolipids,

glycolipids).3. Their derivatives (hormones, fat-

solubility vitamins)By hydrolysis reactions in alkaline hydrolysis reactions in alkaline

solution:solution:1. Saponifiable lipids can be hydrolyzed

under alkaline conditions to yield salts of fatty acids.

2. Nonsaponifiable lipids do not undergo hydrolysis reactions in alkaline solution.

Biological functionsBiological functions The most important role of lipids is as а fuel.

Thus fat is the most concentrated form in which potential energy can be stored.

Since fat is а bad conductor of heat, it provides excellent insulation.

Fat may also provide padding to protect the internal organs.

Some compounds derived from lipids are important building blocks of biologically active materials.

Lipoproteins are constituents of cell membranes. One more important function of dietary lipids is

that of supplying the so-called essential fatty acids

Fatty acidsFatty acids are saponifiable lipid building blocks.

Fatty acids are naturally occurring carboxylic acids with an unbranched carbon chain and an even number of carbon atoms. The pathway by which fatty acids are biosynthesized they almost always contain an even number of carbon atoms. Long-chain fatty acids (12 to 26 carbon atoms) are found in meats and fish; medium-chain fatty acids (6 to 10 carbon atoms) and short-chain fatty acids (fewer than 6 carbon atoms) occur primarily in dairy products.

There are saturated and unsaturated Fatty acids.

• STORE ENERGY

• ALL BIOLOGICAL CELL MEMBRANES

• CHEMICAL MESSENGERS (HORMONES)

• THERMAL AND ELECTRICAL INSULATION (e.g.: NEUROLEMMA THAT SURROUNDS THE AXON)

• MICRONUTRIENTS (FAT-SOLUBLE VITAMINS)

FUNCTIONS AND BIOLOGICAL ROLE

PROCESSES

•HYDROLYSIS OF TRIGLYCERIDES (LIPASE)

•BETA OXIDATION OF FATTY ACIDS

•BIOSYNTHESIS

•SAPONIFICATION

•HYDROGENATION

Saturated fatty acidSaturated fatty acid Fatty acid chains that contain only carbon-carbon single bonds are

referred to as saturated.

Palmitic acid:

Unsaturated fatty acidUnsaturated fatty acidThose molecules that contain one or

more double bonds are said to be unsaturated.

There are mono- and polyunsaturated fatty acids.

Oleic acid:

Essential fatty acids

or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. The term "essential fatty acid" refers to fatty acids required for biological processes but does not include the fats that only act as fuel.Only two fatty acids are known to be essential for humans:

•Alpha-linolenic acid (omega-3)•Linoleic acid (omega-6)

Structure of fatty Structure of fatty acidsacids

Prostaglandins are derivative of fatty polyunsaturated acids

WaxesWaxes

АА wax wax is а monoester formed from the is а monoester formed from the reaction of а long-chain reaction of а long-chain monohydroxy alcohol with а fatty monohydroxy alcohol with а fatty acid molecule. acid molecule.

ExampleExample

The block diagram:

Biological role:Biological role: They serve as protective coatings on leaves, stems, and fruit of plants and the skin and fur of animals.

WAXESBeeswax is a natural wax produced in the bee hive of honey bees of the genus Apis.

Beeswax is a tough wax formed from a mixture of several compounds.An approximate chemical formula for beeswax is C15H31COOC30H61.Its main components are palmitate and esters of long-chain (30–32 carbons) aliphatic alcohols, with the ratio of tricontanyl palmitate CH3(CH2)29O-CO-(CH2)14CH3

Oils and fatsOils and fatsFatty acid esters of the

polyalcohol

glycerol are called acylglycerol or

glicerides; “neutral fat”Reaction formation of

triacylglicerols or

triglyceride

Reaction formation of triacylglicerol

Structure of triacylglycerolor triglyceride

Fat Oil

• cis double bond• folded chain• weak crystalline structure• low melting point• liquid at room temperature

• trans double bond• straight chain• strong crystalline structure• high melting point• solid at room temperature

Chemical propertiesChemical properties

Hydrolysis.Hydrolysis. There is acetic, basic and enzyme’s hydrolysis

Triglycerides

Triglyceride:Triglyceride: An ester of glycerol with three fatty acids.

O

CH2OCR

CH2OCR''

R'COCH

O

O

1. NaOH, H2O

2. HCl, H2O CH2OH

CH2OH

HOCH

RCOOH

R'COOH

R''COOH

A triglyceride 1,2,3-Propanetriol(Glycerol, glycerin)

+

Fatty acids

Saponification

Soaps and Detergents

Natural soaps are prepared by boiling lard or other animal fat with NaOH, in a reaction called saponification (Latin, sapo, soap).

Sodium soaps

1,2,3-Propanetriol(Glycerol; Glycerin)

A triglyceride(a triester of glycerol)

+

saponification+CH

CH2OCR

CH2OCR

CHOH

CH2OH

CH2OH

RCO 3NaOH

3RCO- Na

+

O

O

O

O

COO-Na+

Soaps and Detergents

Soaps clean by acting as emulsifying agents: Their long hydrophobic hydrocarbon chains are

insoluble in water and tend to cluster in such a way as to minimize their contact with water.

Their polar hydrophilic carboxylate groups, on the other hand, tend to remain in contact with the surrounding water molecules.

Driven by these two forces, soap molecules spontaneously cluster into micelles.

Soaps and Detergents

A soap micelle: nonpolar (hydrophobic) hydrocarbon chains cluster in the inside and polar (hydrophilic) carboxylate groups lie on the surface.

Soaps and Detergents

micelle:micelle: A spherical arrangement of organic molecules in water clustered so that their hydrophobic parts are buried inside the sphere and their hydrophilic parts are on the surface of the sphere and in contact with water.

when soap is mixed with water-insoluble grease, oil, and fats, the nonpolar parts of the soap micelles “dissolve” these nonpolar dirt molecules and they are carried away in the polar wash water.

Hydrogenation.

Phospholipides Phosphoacylglycerols are triesters of glycerol in which two -ОН

groups are esterified with fatty acids and one the third is esterified with phosphoric acid, which in turn is esterified to an alcohol.

a)Phosphatidylethanolaminesb)Phosphatidylcholines c)Phosphatidylserines Phosphosphingolipid are esters of dialcohol sphingosine in

which a fatty acid in amide linkage on the amino group and the phosphorylcholine group attached by way of the terminal alcohol group.