biochem lipids i

LIPIDS

Geromil J. Lara, RMT, MSMT

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LIPIDS

• Refers to a collection of organic molecules of varying chemical composition

• Are grouped together on the basis of their solubility in nonpolar solvents

• 4 main groups– Fatty Acids (Saturated and Unsaturated)– Glycerides (Glycerol-containing Lipids)– Nonglyceride Lipids (Sphingolipids,Steroids,Wax)– Complex Lipids (Lipoproteins)

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LIPIDSFatty AcidsSaturated

Unsaturated

GlyceridesNeutral Glycerides

Phosphoglycerides

Complex Lipids

Lipoproteins

Nonglycerides LipidsSphingolipids

Sphingomyelins

Glycolipids

Steroids

Waxes

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BIOLOGICAL FUNCTIONS OF LIPIDS

• Energy Source– When oxidized, each gram of fat releases 9 kcal of

energy, or more than twice the energy released by oxidation of a gram of carbohydrate

• Energy Storage– In the form of triglycerides (TAG) in adipocytes

• Cell Membrane Structural Components– Phosphoglycerides, sphingolipids, and steroids

make up the basic structure of all cell membranes

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BIOLOGICAL FUNCTIONS OF LIPIDS

• Hormones– Steroid Hormones

• Vitamins– Lipid-soluble vitamins (A,D,E, and K)

• Vitamin Absorption– Dietary fat serves as a carrier of the lipid-soluble

vitamins

• Protection – fats as shock absorber• Insulation – subcutaneous fat

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(1) FATTY ACIDS

• Are long-chain monocarboxylic acids

• Generally contain an even number of carbon atoms

O

R C OH

#1 Carbon Acid Group O

R C OH

Non-polar End - Hydrophobic End (Fat-soluble tail)

Polar End - Hydrophilic End

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CLASSIFICATIONS OF FATTY ACID

• Length of the Carbon Chain– Long-chain, medium-chain, short-chain

• Degree of Unsaturation– Saturated, Unsaturated (Mono, Poly)

• Location of Double Bonds– Omega-3 Fatty Acid, Omega-6 Fatty Acid

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(1) FATTY ACIDS

• Short-Chain Fatty Acids– Less than 6 carbons

• Medium-Chain Fatty Acids– 6-10 carbons

• Long-Chain Fatty Acids– More than 12 carbons

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(1) FATTY ACIDS

• Saturated Fatty Acids– Each C being “saturated” with H– General Formula: CH3(CH2)nCOOH

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LAURIC ACID

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(1) FATTY ACIDS

• Unsaturated Fatty Acids– Composed of at least one carbon-to-

carbon double bond– Almost are in the cis configuration

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(1) FATTY ACIDS

• Monounsaturated Fatty Acids (MUFA)– Composed of one carbon-to-carbon double

bond

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(1) FATTY ACIDS

• Polyunsaturated Fatty Acids (MUFA)– Composed of more than one carbon-to-

carbon double bond

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(1) FATTY ACIDS

• Polyunsaturated Fatty Acids (MUFA)– are identified by position of the double

bond nearest the methyl end (CH3) of the carbon chain; this is described as an omega number;

– If PUFA has first double bond 3 carbons away from the methyl end = omega 3 FA

– 6 carbons from methyl end = omega 6 FA

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(1) FATTY ACIDS

• cis-Fatty Acid– H’s on same side of the double bond; fold

into a U-like formation; naturally occurring

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(1) FATTY ACIDS

• trans-Fatty Acid– H’s on the opposite side of the double

bond; occur in partially hydrogenated food

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PROPERTY SATURATED FATTY ACIDS

UNSATURATED FATTY ACID

C-C Bonds within the hydrocarbon

chain

Only C-C single bonds

At least one C-C double bond

Hydrocarbon chains are characteristic of what group of hydrocarbon

Alkanes Alkenes

“Shape” of Hydrocarbon chain

Linear, Fully extended

Bend in carbon chain at site of C-C

double bond

Physical state at room temperature

Solid Liquid

Melting Point Higher Lower

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BUT, ARE ALL TRANS-FAT BAD?

• Omega-3: – Eicosopentaenoic acid (EPA)– Docosahexaenoic acid (DHA)– Alpha-linolenic acid (ALA)

• flaxseed--most, canola (rapeseed), soybean, walnut, wheat germ

• body can make some EPA and DHA from ALA

• Omega-6– corn, safflower, cottonseed, sesame,

sunflower– Linoleic acid

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CHEMICAL REACTIONS OF FATTY ACID

• Esterification – Fatty acids react with alcohols to form

esters and water

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• Acid Hydrolysis – Producing fatty acids from esters– Opposite of esterification

• Saponification– Is the base-catalyzed hydrolysis of an

ester– the product of this reaction, an ionized

salt, is a soap• Have a long uncharged hydrocarbon tail and a

negatively charged terminus (the carboxylate terminus

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• Saponification– Is the base-catalyzed hydrolysis of an

ester

– the product of this reaction, an ionized salt, is a soap• Have a long uncharged hydrocarbon tail and a

negatively charged terminus (the carboxylate terminus), they form micelles that dissolve oil and dirt particles

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• Reaction at the Double Bond (Unsaturated Fatty Acids)– Hydrogenation

• Used in the food industry to convert polyunsaturated vegetable oils into saturated solid fats

– Partial Hydrogenation• Carried out to add hydrogen to some, but not

all, double bonds in polyunsaturated oils• In this way liquid vegetable oils are converted

into solid form (Crisco and margarine)

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(2) GLYCERIDES

• Are lipid esters that contain the glycerol molecule and fatty acids– 2 Classes

• Neutral Glycerides – nonionic and nonpolar

• Phosphoglycerides – have polar region, the phosphoryl group, in addition to the nonpolar fatty acid tails

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(2) GLYCERIDES

• Neutral Glycerides– Produce after the esterification of glycerol

with a fatty acid– Esterification may occur at one, two, or all

three positions, producing:• Monoglycerides• Diglycerides• Triglycerides – most important and main

storage form of lipids in man (adipocytes)

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FAT vs. OIL

• Fat – A mixture of triglycerides containing high

proportion of long-chain, saturated fatty acids• Animals – generally solids• Plants or Fish – usually liquids

• Oil– Liquid fat– Contain high proportion of unsaturated

fatty acids and saturated fatty acids

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(2) GLYCERIDES

• Neutral Glycerides– There are no charges (+ or -) on these

molecules– These long molecules readily stack with

one another and constitute the majority of the lipids stored in the body’s fat cells

– Primary function is to store energy• More energy-rich nutrients are consumed than

are required for metabolic processes, much of the excess is converted to neutral glycerides and stored as TAG in fat cells

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(2) GLYCERIDES

• Phosphoglycerides– Phospholipids – are

group of lipids that are phosphate esters• The presence of the

phosphoryl group results in a molecule with a polar head (the phosphoryl group) and a nonpolar tail (the alkyl chain of the fatty acid)

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(2) GLYCERIDES

• Phosphoglycerides– Most abundant membrane lipids and

derived from glycerol-3-phosphate– Contain acyl groups derived from long

chain fatty acids at C-11 and C-2 of glycerol-3-phosphate

– At C-3 the phosphoryl group is joined to glycerol by a phosphoester bond• Phosphatidate – simplest phosphoglyceride

contains a free phosphoryl group

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