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BIOLOGY SBI3UIModule 1: Chemical basis of life

Activity 2B. Lipids

By: Miss Kasthuri

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Outline

Types of LipidsStructures of Lipids

Fatty AcidsFats, and Oils

Chemical Properties of Triglycerides

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Lipids

Lipids are• Biomolecules that contain fatty acids or a

steroid nucleus.• Soluble in organic solvents but not in water.• Named for the Greek word lipos, which means

“fat.”• Extracted from cells using organic solvents.

Lipids

• Hydrophobic, non-polar molecules• energy storage

– a lot of calories in a small space• generally insoluble in water

– stored in special ways in the body• also function as structural components of cells

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Types of Lipids

Lipids with fatty acids Waxes. Fats and oils (triacylglycerols). Glycerophospholipids. Prostaglandins.

Lipids without fatty acids Steroids

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Structures of Lipids

Fatty Acids

• made up of carbon, hydrogen, oxygen– more carbon and hydrogen so they supply more

energy/gram• common building block for most lipids

fatty acids

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Fatty Acids

• Long-chain carboxylic acids• Insoluble in water• Typically 12-18 carbon atoms (even number)• Some contain double bonds

corn oil contains 86% unsaturated fatty acids and

14% saturated fatty acids

the determining factor in whether to call a fatty acid saturated, unsaturated, monounsaturated, polyunsaturated, or trans fatty is determined by its chemical bonds and structure

Fatty Acids

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Saturated and Unsaturated Fatty Acids

Saturated = C–C bondsUnsaturated = one or more C=C bonds

COOH

COOH

palmitoleic acid, an unsaturated fatty acid

palmitic acid, a saturated acid

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Structures

Saturated fatty acids• Fit closely in regular pattern

Unsaturated fatty acids• Cis double bonds

COOHCOOHCOOH

C CH H

COOHcis double bond

Properties of SaturatedFatty Acids

• Contain only single C–C bonds• Closely packed • Strong attractions between chains• High melting points• Solids at room temperature

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Properties of UnsaturatedFatty Acids

• Contain one or more double C=C bonds• Nonlinear chains do not allow molecules

to pack closely• Few interactions between chains• Low melting points• Liquids at room temperature

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Waxes, Fats, and Oils

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Waxes

Waxes are Esters of saturated fatty acids and long-chain alcohols. Coatings that prevent loss of water by leaves of plants.

TABLE 17.2

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Fats and Oils: Triacylglycerols

Fats and oils are Also called triacylglycerols. Esters of glycerol. Produced by esterification. Formed when the hydroxyl

groups of glycerol react with the carboxyl groups of fatty acids.

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Esterification

• When glycerol combines with each fatty acid, a condensation reaction (dehydration synthesis) takes place

• An acid reacting with an alcohol produces an ester linkage, hence this process is called as esterification.

Triglycerides• the form of lipid most found in food

– 3 fatty acids + glycerol– Glycerol is an alcohol, while the

fatty acids are an acidic carboxyl group combined with long hydrocarbon chain.

– major class of dietary lipid– flabby stuff most of us have is

cells filled with triglycerides

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Melting Points of Fats and Oils

A triacylglycerol that is a fat Is solid at room temperature. Is prevalent in meats, whole milk, butter, and cheese.

A triacylglycerol that is an oil Is liquid at room temperature. Is prevalent in plants such as olive and safflower.

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Chemical Properties of Triacylglycerols

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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The chemical reactions of triacylglycerols are similarto those of alkenes and esters. In hydrogenation, double bonds in unsaturated

fatty acids react with H2 in the presence of a Ni or Pt catalyst.

In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme.

Chemical Properties of Triacylglycerols

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Hydrogenation

Adds hydrogen (H2) to the carbon atoms of double bonds. Converts double bonds to single bonds. The process is done using an enzyme and hydrogen gas TRANS fatty acids or Trans fat Produces solids such as margarine and shortening.

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Hydrogenation

Ni + 3H2

glyceryl tripalmitoleate (tripalmitolean)

glyceryl tripalmitate(tripalmitin)

O

(CH2)14CH3C

O

(CH2)14CH3C

O

(CH2)14CH3C

O

O

OCH2

CH2

CH

CH(CH2)7CH3(CH2)5CH

O

C

CH(CH2)7CH3(CH2)5CH

O

C

CH(CH2)7CH3(CH2)5CH

O

C

O

O

OCH2

CH2

CH

Trans-Fatty Acids

hydrogenated fatty acids more saturated than natural vegetable oils able to pack together more tightly more solid are room temperature behave more like saturated fatty acids

hidden in the reporting levels for unsaturated fatty acids

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HydrolysisIn hydrolysis, Triacylglycerols split into glycerol and three fatty acids. An acid or enzyme catalyst is required.

OCH2

OCH

OCH2

OHCH2

OHCH

OHCH2

O

(CH2)14CH3CHO

H2OO

(CH2)14CH3C

O

(CH2)14CH3C

O

(CH2)14CH3C

H++3

+ 3

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Glycerophospholipids are The most abundant lipids in cell membranes. Composed of glycerol, two fatty acids, phosphate

and an amino alcohol.

Glycerol

PO4Amino alcohol

Glycerophospholipids

Fatty acid

Fatty acid

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Glycerophospholipids Are Polar

A glycerophospholipid has Two nonpolar fatty acid chains. A phosphate group and a polar amino alcohol. CH3

│+ +

HO−CH2−CH2−N−CH3 HO−CH2−CH2−NH3

│ choline CH3 ethanolamine +

NH3

│ Amino alcohols HO−CH2−CH−COO−

serine

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Structure and Polarity of A Glycerophospholipid

Sterols (Steroids)

Lipids without fatty acids Highly hydrophobic important players: bile, sex hormones, Vit D

cholesterol is starting material cholesterol

only found in food derived from animals “good” or “bad “ cholesterol is not a type of cholesterol

found in food refers to the transportation of cholesterol in the blood

made in liver from carbs, protein, fat 800-1500 milligrams/day

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Other steroids - Steroid Hormones

Steroid hormones Are chemical

messengers in cells. Are produced from

cholesterol. Include sex hormones

such as androgens (testosterone) in males and estrogens (estradiol) in females.

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings