Lipids. There are 2 types of lipids; those that contain the structural component of a fatty acid; and

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 nonpolar organic solvents. • natural components of cell membranes, fat-soluble

Lipids

There are 2 types of lipids;

• those that contain the structural component of a fatty acid; and

• those that contain the structural component of a four member steroid molecule.

Types of Lipids

The lipids that contain fatty acids are • waxes,

• fats and oils (triacylglycerols), • glycerophospholipids, and

• prostaglandins.

The types of lipids that do not contain fatty acid chains are steroids.

Learning Check

A. steroids and waxes

B. triacylglycerols and glycerophospholipids C. sphingolipids and glycerophospholipids D. glycerophospholipids and waxes

Solution

A. steroids and waxes

B. triacylglycerols and glycerophospholipids C. sphingolipids and glycerophospholipids D. glycerophospholipids and waxes

Answer is B. Triacylglycerols and glycerophospholipids contain the alcohol glycerol.

Fatty Acids

• are insoluble in water. • can be saturated or

Fatty Acid Formulas

The formulas for fatty acids are written as • condensed structural formulas.

Saturated Fatty Acids

Saturated fatty acids have

• only single C—C bonds.

• molecules that fit closely together in a regular pattern.

Saturated Fatty Acids

Unsaturated Fatty Acids

Unsaturated fatty acids

• have one or more double bond.

• that are naturally occurring have one or more cis double bond

Monounsaturated Fatty Acids

Unsaturated fatty acids with one double bond are called monounsaturated fatty acids.

Polyunsaturated Fatty Acids

Unsaturated fatty acids with more than one double bond are called polyunsaturated fatty acids.

Properties of Saturated

Fatty Acids

Saturated fatty acids

• fit closely together in

a regular pattern.

• are solids at room

Properties of

Unsaturated Fatty Acids

Unsaturated fatty acids

• have ―kinks‖ in the

fatty acid chains.

• do not pack closely.

• are liquids at room

temperature.

―kinks‖ in chain

Prostaglandins

Prostaglandins have

• 20 carbon atoms in their fatty acid chains.

Prostaglandins and

Physiological Effects

Prostaglandins have potent physiological effects. • Some increase blood pressure.

• Some lower blood pressure.

• Some stimulate contractions and relaxation of smooth

muscle in the uterus during the birth process and menstrual cycle.

When tissues are injured, arachidonic acid in the blood is converted to PGE₁ and PGF₂ that produce

NSAIDs and Prostaglandins

Several nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, block production of prostaglandins decreasing pain, inflammation, and fever.

NSAIDs and Prostaglandins

Other NSAIDs include naproxen (Aleve and Naprosyn), ketoprofen (Actron), and nabumetone (Relafen).

Long-term use of such products can result in liver, kidney, and gastrointestinal damage.

Omega-3 and Omega-6

Fatty Acids

Fish and vegetable oils have high levels of unsaturated fats.

 In vegetable oils, they are mostly omega-6 with the first at C6.

Linoleic acid

 In fish oils, they are mostly omega-3 with the first at C3.

CH₃─CH₂─(CH═CH─CH₂)₃─(CH₂)₆─COOH

1 3

Omega-6 and Omega-3 Fatty

Acids

Omega-3 Fatty Acids

• lower the tendency of blood platelets to stick together, thereby reducing the possibility of blood clots.

• can help reduce risk of heart disease. • are found in salmon, tuna, and herring.

Learning Check

Draw the condensed structural formulas for each of the fatty acids with 10 carbon atoms that follow.

Learning Check

Draw the condensed structural formulas for each of the fatty acids with 10 carbon atoms that follow.

Learning Check

Draw the condensed structural formulas for each of the fatty acids with 10 carbon atoms that follow.

Solution

Draw the condensed structural formulas for each of the fatty acids with 10 carbon atoms that follow.

A. saturated

CH₃—CH₂—CH₂—CH₂—CH₂—CH₂—CH₂—CH₂—CH₂—COOH

B. monounsaturated omega-3

Waxes

Waxes are

• esters of saturated fatty acids and long-chain alcohols each containing 14 to 30 carbon atoms.

Fats and Oils:

Triacylglycerols

Fats and oils are

• also called triacylglycerols.

• triesters of glycerol.

• produced by esterification.

• formed when the hydroxyl

groups of glycerol react with the

carboxyl groups of fatty acids.

• a major form of energy storage

for animals

.

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Triacylglycerols

In a triacylglycerol, glycerol forms ester bonds with three fatty acids.

Formation of a

Triacylglycerol

• Most naturally occurring fats and oils are mixed

triacylglycerols that contain glycerol bonded by ester bonds to two or three different fatty acids, typically palmitic acid, linoleic acid, and stearic acid.

Learning Check

Draw the condensed structural formula for glyceryl tripalmitoleate (tripalmitolein).

Solution

Draw the condensed structural formula for glyceryl tripalmitoleate (tripalmitolein).

Fats and Oils

• Fats and oils are one of the three energy sources provided by diet.

• Nutritionists recommend that less than 30% of the daily dietary caloric intake by derived by fats.

• Fats provide more energy per gram than carbohydrates and protein

• When calculating calories from fat, multiply by 9, for carbs and protein multiple by 4.

Properties of Fats and Oils

A triacylglycerol that is usually called a fat • is solid at room temperature.

• is prevalent in meats, whole milk, butter, and cheese.

A triacylglycerol that is usually called an oil • is liquid at room temperature.

Oils with Unsaturated

Fatty Acids

Oils

• have more unsaturated fats.

• have cis double bonds that cause ―kinks‖

in the fatty acid chains.

• cannot pack triacylglycerol molecules as

closely together as in fats.

Triacylglycerol with

Unsaturated Fatty Acids

Unsaturated fatty acid chains have kinks that do not allow close

packing, such as those in olive oil.

Saturated and Unsaturated Fatty

Acids In Fats and Oils

Vegetable oils are liquids at room temperature because they have a higher percentage of unsaturated fatty acids than do animal fats.

Chemical Properties of

Triacylglycerols

The chemical reactions of triacylglycerols are similar to 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.

Hydrogenation of

Glyceryl Trioleate

In a hydrogenation reaction, H₂ adds across

the double bond to form a carbon–carbon single bond.

Hydrogenation of Oils

The hydrogenation of oils

• converts double bonds to single bonds,

• adds hydrogen (H₂) to the carbon atoms of double bonds, • produces solids, such as margarine and shortening

Cis and Trans Fatty Acids

Unsaturated fatty acids can be

• cis with bulky groups on the same side of , or

Trans Fatty Acids and

Hydrogenation

Trans fatty acids

• are formed during hydrogenation when cis double bonds are converted to an undesirable side product with a trans double bond.

• in the body behave like saturated fatty acids.

• are estimated to make up 2–4% of our total calories.

The American Heart Association recommends the use of soft margarine, which is only slightly hydrogenated and therefore has fewer trans fatty acids.

Trans Fats

In vegetable oils,

• the unsaturated fats usually contain cis double bonds. • during hydrogenation, some cis double bonds are

converted to trans double bonds (more stable), causing a change in the fatty acid structure.

Learning Check

Identify each statement as true (T) or false (F).

A. There are more unsaturated fats in vegetable oils.

B. Hydrogenation of oils converts some cis-double bonds to trans-double bonds.

Solution

Identify each statement as true (T) or false (F).

T A. There are more unsaturated fats in vegetable oils. T B. Hydrogenation of oils converts some cis-double bonds to trans-double bonds.