Chapter 21

Lipids

Chemistry B11

Lipids

- Family of bimolecules.

- They are not defined by a particular functional group, thus they have a variety of structures and functions.

- They are soluble in organic solvents but not in water (nonpolar).

- They contain many nonpolar C—C and C—H bonds and few polar bonds resulting in their water insolubility.

Lipids

1. Store energy: fat cells

2. Chemical messengers: find in nerve fibers and hormones.

3. Parts of membranes: insoluble in water

Lipids

Lipids

1. Simple lipids: (Waxes, Fats & Oils)

2. Complex lipids (Glycerophospholipids)

3. Steroid (Cholesterol & steroid hormones)

4. Eicosanoids

Store energy, insulation

Cell membrane

Chemical messengerCell membrane

Pain, fever, inflammation

Fatty acids

Fatty acids are:

• Long-chain unbranched carbon attached to a carboxyl group.

• Typically 12-18 carbon atoms.

• Insoluble in water.

• Saturated or unsaturated. COOH

COOH

COOH

COOH

Stearic acid (18:0)(mp 70°C)

Oleic acid (18;1)(mp 16°C)

Linoleic acid (18:2)(mp-5°C)

Linolenic acid (18:3)(mp -11°C)

Cis

COOH

COOH

COOH

COOH

Stearic acid (18:0)(mp 70°C)

Oleic acid (18;1)(mp 16°C)

Linoleic acid (18:2)(mp-5°C)

Linolenic acid (18:3)(mp -11°C)

Saturated and unsaturated Fatty acids

COOH

COOH

COOH

COOH

COOH

COOH

COOH

COOH

COOH

COOH

Saturated fatty acids are solids at room temperature.

Packed together Maximum London dispersion forces

Unsaturated fatty acids are liquids at room temperature.

Can not pack together London dispersion forces

• The human body is capable of synthesizing most fatty acids from

carbohydrates or other fatty acids.

• Humans do not synthesize sufficient amounts of fatty acids that

have more than one double bond.

• More than one double bond fatty acids are called essential fatty

acids and they must be provided by the diet.

Fatty acids

Long-chain alcohol Fatty acidEster bond

Waxes

- are found in many plants and animals (or humans).

- In plants, they help prevent loss of water and damage from pests.

- In humans and animals, provide waterproof coating on skin and fur.

Wax is an ester of saturated fatty acid and long chain alcohol.

For example, shown below is the formation of spermaceti wax, isolated from the heads of sperm whales.

Waxes

Acid

Beeswax CarnaubaCoating

Jojoba

Lanolin from wool lotions

Triacylglycerols are:

• Fats and oils (are stored in the body).

• Triesters of glycerol.

• Produced by Fischer esterification.

• Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids.

Triacylglycerols (Triglycerides)

glycerol three fatty acids triacylglycerol

OHCH2

OH

OHCH2

CHO

(CH2)14CH3CHO

O

(CH2)14CH3CHO

O

(CH2)14CH3CHO

+ 3H2O

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

Esterification

Acid

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

GLYCEROL

Fatty acid

Fatty acid

Fatty acid

Triacylglycerols (Triglycerides)

Produced by esterification of glycerol (a trihydroxyl alcohol).

CH2

CH

CH2

OH

OH

OH

Glycerol

Triacylglycerols (Triglycerides)

Fat: is a triacylglycerol that is solid at room temperature.

Made by more saturated fatty acids (Saturated triacylglycerols).

Meat, milk, butter and cheese (animal sources).

Oil: is a triacylglycerol that is liquid at room temperature.

Made by more unsaturated fatty acids (Unsaturated triacylglycerols).

Corn, cotton seed, safflower and sunflower (plant sources).

Both are colorless, odorless, and tasteless.

- Hydrogen adds to the double bonds of unsaturated fats (using transition

metal catalyst such as Ni).

- Melting point is increased.

- Liquid oils are converted to semisolid fats.

Hydrogenation

_C=C_ + H2 → _C_C_Ni

H H

H H

H H

Ni

+ 3H2

glyceryl Trioleate (triolein)

glyceryl tristearate (tristearin)

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

1- Hydrogenation

2- Hydrolysis

Triacylglycerols are hydrolysis (split by water) in the presence of strong acid or lipase (digestive enzyme).

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

+ 3H2O

Na+ -O

O

C (CH2)14CH3+H+ or Lipase

OH

CH OH

CH2 OH

CH2

3HO

• Is the process of forming “soaps” (salts of fatty acids).

• Is the reaction of a fat with a strong base (NaOH).

• Splits triacylglycerols into glycerol and the salts of fatty acids.

• With KOH or the oils that are polyunsaturated gives softer soaps (liquid soaps).

• Name of soap gives the source of the oil.

3- Saponification

Like coconut or avocado soap

O

O

C (CH2)14CH3

CH O

O

C (CH2)14CH3

CH2 O

O

C (CH2)14CH3

CH2

+ 3NaOH

Na+ -O

O

C (CH2)14CH33

OH

CH OH

CH2 OH

CH2

+

“soap”

Heat

Salt of fatty acid

3- Saponification (Basic Hydrolysis)

GLYCEROL

Fatty acid

Fatty acid

phosphateAminoalcohol

Glycerophospholipids

Polar part (polar head) and nonpolar part (nonpolar tail)

P

O

OO

O_

N

CH3

HO – CH2 _ CH2

CH3

CH3

+

Interact with both polar and nonpolar substances.

1. Most abundant lipids in cell membranes (semipermeable).

2. Combine with less polar triglycerides and cholesterol to make them soluble.

Choline

Steroids have:

• A steroid nucleus which is 4 carbon rings.

• Attached groups that make the different types of compounds.

• No fatty acids. steroid nucleus

Steroids

Cholesterol:

• Is the most abundant steroid in the body.

• Insoluble in water (need a water soluble carrier).

• Has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus.

CH3

CH3CH3

CH3

HO

CH3

Cholesterol

Cholesterol:

• Is obtained from meats, milk, and eggs.

• Is synthesized in the liver from fats, carbohydrates and proteins.

• Is needed for cell membranes, brain and nerve tissue, steroid hormones, and Vitamin D.

• Clogs arteries when high levels form plaque.

• No cholesterol in vegetable and plants.

At artery clogged by cholesterol plaque

Cholesterol

Gallstones form in gallbladder

Steroid hormones are:

Chemical messengers in body

Sex hormones

Testosterone & androsterone in males Estrogen & progesterone in females

OHCH3

CH3

HO

OHCH3

CH3

O

Testosterone (androgen)Male sex hormone

EstrogenFemale sex hormone

Steroids

Triacylglycerols

Lipoproteins

Transporting lipids through the bloodstream to tissues where they are stored, Used for energy, or to make hormones.

Spherical particles

Polar surface and nonpolar inner

Water-soluble form of lipids

(soluble in blood)

Lipoproteins

VLDL: very-low-density lipoprotein

Liver Fat storage cells

Heart and muscles

LDL

VLDL

HDLEnergyIntestine

andelimination

Triglycerides and Cholesterol

LDL: low-density lipoprotein (bad Cholesterol) Cholesterol

Chylomicrons Triglycerides and Cholesterol

HDL: high-density lipoprotein (good Cholesterol) Cholesterol

Recommended levels are: HDL > 40 mg/dL, LDL < 100 mg/dL, total serum cholesterol < 200 mg/dL.

Cell Membrane

Semipermeable: nutrients can enter and waste products can leave.

Fluid mosaic model

NonpolarPolar

Phospholipidbilayer

Carbohydrate