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LipidsLipids are the hydrophobic compounds of C, H and OWith much higher ratio of hydrogen to oxygen than carbohydrates

Most are insoluble in water but soluble in non polar compounds

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Lipids

Types of Lipids

Fatty Acids

Fats, and Oils

Chemical Properties of Triglycerides

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Properties of fats and oils

• fats are solids or semi solids• oils are liquids• melting points and boiling points are not

usually sharp (most fats/oils are mixtures)• when shaken with water, oils tend to emulsify• pure fats and oils are colorless and odorless

(color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)

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Examples of oils

• Olive oil – from Oleo europa (olive tree)• Corn oil – from Zea mays• Peanut oil – from Arachis hypogaea• Cottonseed oil – from Gossypium• Sesame oil – from Sesamum indicum• Linseed oil – from Linum usitatissimum• Sunflower seed oil – from Helianthus annuus• Rapeseed oil – from Brassica rapa• Coconut oil – from Cocos nucifera

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Non-drying, semi-drying and drying oils

• based on the ease of autoxidation and polymerization of oils (important in paints and varnishes)

• the more unsaturation in the oil, the more likely the “drying” process– Non-drying oils:

• Castor, olive, peanut, rapeseed oils

– Semi-drying oils• Corn, sesame, cottonseed oils

– Drying oils• Soybean, sunflower, hemp, linseed, tung, oiticica oils

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Types of Lipids

• Lipids with fatty acids

Waxes

Fats and oils (trigycerides)

Phospholipids

Sphingolipids

• Lipids without fatty acids

Steroids

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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

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Saturated and Unsaturated Fatty Acids

Saturated = C–C bonds

Unsaturated = 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

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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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Fatty acids

• Common fatty acids

n = 4 butyric acid (butanoic acid)

n = 6 caproic acid (hexanoic acid)

n = 8 caprylic acid (octanoic acid)

n = 10 capric acid (decanoic acid)

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Fatty acids

• common FA’s: n = 12: lauric acid (n-dodecanoic acid; C12:0)

n = 14: myristic acid (n-tetradecanoic acid; C14:0)

n = 16: palmitic acid (n-hexadecanoic acid; C16:0)

n = 18; stearic acid (n-octadecanoic acid; C18:0)

n = 20; arachidic (eicosanoic acid; C20:0)

n= 22; behenic acid

n = 24; lignoceric acid

n = 26; cerotic acid

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Typical fish oil supplements

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Learning Check L1

How would the melting point of stearic acid compare to the melting points of oleic acid and linoleic acid? Assign the melting points of –17°C, 13°C, and 69°C to the correct fatty acid. Explain.

stearic acid (18 C) saturated

oleic acid (18 C) one double bond

linoleic acid (18 C) two double bonds

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Solution L1

Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Because linoleic has two double bonds, it would have a lower mp than oleic acid, which has one double bond.

stearic acid mp 69°C

oleic acid mp 13°C

linoleic acid mp -17°C

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Fats and Oils

Formed from glycerol and fatty acids

+

HO C (CH2)14CH3

O

HO C (CH2)14CH3

O

HO C (CH2)14CH3

O

glycerol palmitic acid (a fatty acid)

CH

CH2 OH

OH

CH2 OH

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Triglycerides (triacylglcerols)

Esters of glycerol and fatty acids

CH

CH2

CH2 O

O

O

C (CH2)14CH3

O

C (CH2)14CH3

O

C (CH2)14CH3

O

ester bonds

+

+

+

H2O

H2O

H2O

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Learning Check L2

What are the fatty acids in the following triglyceride?

CH

CH2

CH2 O

O

O

C (CH2)16CH3

O

C

O

(CH2)7CH CH(CH2)7CH3

C

O

(CH2)12CH3

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Solutions L2

What are the fatty acids in the following triglyceride?

CH

CH2

CH2 O

O

O

C (CH2)16CH3

O

C

O

(CH2)7CH CH(CH2)7CH3

C

O

(CH2)12CH3

Stearic acid

Oleic acid

Myristic acid

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Properties of Triglycerides

Hydrogenation• Unsaturated compounds react with H2

• Ni or Pt catalyst• C=C bonds C–C bonds

Hydrolysis• Split by water and acid or enzyme catalyst• Produce glycerol and 3 fatty acids

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Hydrogenation

CH

CH2

CH2 O

O

O

C

O

(CH2)5CH CH(CH2)7CH3

C

O

(CH2)5CH CH(CH2)7CH3

C

O

+

(CH2)5CH CH(CH2)7CH3

H23Ni

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Hydrogenated fats

• hydrogenation leads to either saturated fats and or trans fatty acids

• the purpose of hydrogenation is to make the oil/fat more stable to oxygen and temperature variation (increase shelf life)

• example of hydrogenated fats: Crisco, margarine

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Product of Hydrogenation

Hydrogenation converts double bonds in oils to single bonds. The solid products are used to make margarine and other hydrogenated items.

CH

CH2

CH2 O

O

O

C (CH2)14CH3

O

C (CH2)14CH3

O

C (CH2)14CH3

O

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Hydrolysis

Triglycerides split into glycerol and three fatty acids (H+ or enzyme catalyst)

CH

CH2

CH2 O

O

O

C (CH2)14CH3

O

C (CH2)14CH3

O

C (CH2)14CH3

O H2O+3

3+ HO C (CH2)14CH3

O

CH

CH2 OH

OH

CH2 OH

H+

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Saponification and Soap

• Hydrolysis with a strong base• Triglycerides split into glycerol and the

salts of fatty acids • The salts of fatty acids are “soaps”• KOH gives softer soaps

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Saponification

3+ Na+ -O C (CH2)14CH3

O

CH

CH2 OH

OH

CH2 OH

CH

CH2

CH2 O

O

O

C (CH2)16CH3

O

C

O

(CH2)16CH3

(CH2)16CH3C

O

+ 3 NaOH

salts of fatty acids (soaps)

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Soaps• Process of formation is known as

saponification– Types of soaps:

• Sodium soap – ordinary hard soap• Potassium soap – soft soap (shaving soaps are

potassium soaps of coconut and palm oils)• Castile soap – sodium soap of olive oil• Green soap – mixture of sodium and potassium linseed

oil• Transparent soap – contains sucrose• Floating soap – contains air• Calcium and magnesium soaps are very poorly water

soluble (hard water contains calcium and magnesium salts –these insolubilize soaps)

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Learning Check L3

What are the products obtained from the complete hydrogenation of glyceryl trioleate?

(1) Glycerol and 3 oleic acids

(2) Glyceryltristearate

(3) Glycerol and 3 stearic acids

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Solution L3

What are the products obtained from the complete hydrogenation of glyceryl trioleate?

2. Glyceryltristearate

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Lipids

Phospholipids

Steroids and Cholesterol

Plasma (Cell)Membranes

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Phosphoglycerides

• Most abundant lipids in cell membranes • Control cell permeability

FATTY ACID

FATTY ACIDglycerol

PO4Amino alcohol

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Steroids

• Steroid nucleus• 3 cyclohexane rings• 1 cyclopentane ring

steroid nucleus

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Cholesterol

• Most abundant steroid in the body

• Add methyl CH3- groups, alkyl chain, and -OH to steroid nucleus

CH3

HO

CH3

CH3 CH3

CH3

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Cholesterol in the Body

• Cellular membranes

• Myelin sheath, brain, and nerve tissue

• Bile salts

• Hormones

• Vitamin D

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Bile Salts

• Synthesized in the liver from cholesterol

• Stored in the gallbladder

• Secreted into small intestine

• Mix with fats to break them part

• Emsulsify fat particles

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Steroid Hormones

• Chemical messengers in cells• Sex hormones

Androgens in males (testosterone)

Estrogens in females (estradiol)• Adrenocorticosteroids from adrenal glands

mineralocorticoids (electrolyte balance)

glucocorticoids regulate glucose level

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Sex Hormones

O

CH3

CH3OH

HO

CH3

CH3OH

testosterone estradiol

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Plasma Membranes

• Surround cells

• Lipid bilayer pf phospholipids

• Nonpolar hydrocarbon tails in center

• Polar (hydrophilic) sections on outside

• Some unsaturated fatty acids give flexibility

• Keep aqueous contents inside

• Allow certain biochemicals to pass through

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Diagram of a Plasma Membrane

Polar sections

Nonpolar tails