5.1 - The Chemist’s View of Fatty Acids and Triglycerides

Recognize the chemistry of fatty acids and triglycerides and the differences between saturated and unsaturated fats.

Lipids

a family of compounds that includes triglycerides, phospholipids, and sterols. Lipids are characterized by their insolubility in water. (Lipids also include the fat-soluble vitamins.)

What elements make up lipids?

Carbon (C), hydrogen (H), and oxygen (O)

Why do lipids provide more energy per gram than carbohydrates?

Lipids contain proportionally more carbon and hydrogen and less oxygen than carbohydrates.

How does the chemical structure of a triglyceride appear?

It resembles the letter “E.”

What is a triglyceride made of?

One glycerol molecule with three fatty acids attached.

What is glycerol?

A three-carbon alcohol that forms the backbone of a triglyceride.

What are fatty acids?

Chains of carbon atoms attached to glycerol in triglycerides.

How long can fatty acid chains be?

Between 4 and 24 carbons, always in even numbers.

Which fatty acid chain length is most common in foods?

18-carbon fatty acids.

What are the two main types of fatty acids?

Saturated and unsaturated fatty acids

What does “unsaturated” mean in fatty acids?

The fatty acid contains one or more points of unsaturation (double bonds).

What is a monounsaturated fatty acid?

A fatty acid with one point of unsaturation (one double bond).

What is a polyunsaturated fatty acid?

A fatty acid with two or more points of unsaturation (multiple double bonds).

Which polyunsaturated fatty acids are especially important in nutrition?

Omega-3 fatty acids and omega-6 fatty acids.

What are the two essential 18-carbon polyunsaturated fatty acids?

Linolenic acid (omega-3) and linoleic acid (omega-6).

Why are linolenic acid (omega-3) and linoleic acid (omega-6) considered essential fatty acids?

The body cannot make them, so they must be obtained from food.

What role do omega-3 and omega-6 fatty acids play in the body?

They are the starting materials for longer-chain fatty acids that regulate blood pressure, blood clotting, and other important body functions.

Fatty Acids

organic compounds composed of carbon chains with hydrogens attached. Each fatty acid has an acid group (COOH) at one end and a methyl group (CH3) at the other end.

What is the basic structure shared by all fatty acids?

A chain of carbon and hydrogen atoms with an acid group (COOH) at one end and a methyl group (CH₃) at the other.

In what two main ways do fatty acids differ from one another?

Length of the carbon chain and number/location of double bonds.

How many carbons do most naturally occurring fatty acids contain?

Even numbers of carbons, up to 24.

What is stearic acid?

The simplest 18-carbon fatty acid with no double bonds.

What types of fatty acids are most common in the diet?

Long-chain fatty acids (more than 12 carbons).

Where are medium- and short-chain fatty acids most commonly found?

Primarily in dairy products.

What defines long-, medium-, and short-chain fatty acids?

• Long-chain: >12 carbons

• Medium-chain: 8–12 carbons

• Short-chain: up to 6 carbons

What is a saturated fatty acid?

A fatty acid with no double bonds and the maximum number of hydrogen atoms.

Why must a double bond form if hydrogens are missing from a fatty acid?

Each carbon must have four bonds to satisfy chemical bonding rules.

What is a point of unsaturation?

A carbon–carbon double bond in a fatty acid.

What is an unsaturated fatty acid?

A fatty acid with one or more double bonds.

What is a monounsaturated fatty acid?

A fatty acid with one double bond.

What is a polyunsaturated fatty acid?

A fatty acid with two or more double bonds.

What type of fatty acid is stearic acid?

An 18-carbon saturated fatty acid.

What type of fatty acid is oleic acid?

An 18-carbon monounsaturated fatty acid.

What oils are rich in oleic acid?

Olive oil and canola oil.

What type of fatty acid is linoleic acid?

An 18-carbon polyunsaturated fatty acid with two double bonds.

OR

An 18-carbon polyunsaturated fatty acid with three double bonds.

monounsaturated fatty acid

a fatty acid that lacks two hydrogen atoms and has one double bond between carbons; abbreviated MUFA. Examples include palmitoleic acid and oleic acid. A monounsaturated fat is composed of triglycerides in which most of the fatty acids are monounsaturated. • mono = one

point of unsaturation

the double bond of a fatty acid, where hydrogen atoms can easily be added to the structure.

polyunsaturated fatty acid

a fatty acid that lacks four or more hydrogen atoms and has two or more double bonds between carbons; abbreviated PUFA. Examples include linoleic acid (two double bonds) and linolenic acid (three double bonds). A polyunsaturated fat is composed of triglycerides in which most of the fatty acids are polyunsaturated. • poly = many

saturated fatty acid

a fatty acid carrying the maximum possible number of hydrogen atoms—for example, stearic acid. A saturated fat is composed of triglycerides in which most of the fatty acids are saturated.

unsaturated fatty acid

a fatty acid that lacks hydrogen atoms and has at least one double bond between carbons (that is, a monounsaturated or polyunsaturated fatty acid). An unsaturated fat is composed of triglycerides in which most of the fatty acids are unsaturated.

Which 18-carbon fatty acid has the most double bonds?

Linolenic acid (3 double bonds).

What foods are major sources of linoleic acid with two double bonds?

Sunflower, safflower, corn, and soybean oils.

What foods are major sources of linoleic acid with three double bonds?

Soybean and canola oils, flaxseed, and walnuts.

What does the shorthand notation “18:0” mean?

An 18-carbon fatty acid with zero double bonds.

In fatty acid shorthand notation, what do the two numbers represent?

First number = number of carbons; second number = number of double bonds.

How are omega fatty acids classified?

By the position of the double bond closest to the methyl end of the chain.

What defines an omega-3 fatty acid?

The closest double bond is three carbons from the methyl end.

What defines an omega-6 fatty acid?

The closest double bond is six carbons from the methyl end.

What omega family does linolenic acid with three double bonds belong to?

Omega-3

What omega family does linolenic acid with two double bonds belong to?

Omega-6

What omega family do most monounsaturated fatty acids belong to?

Omega-9

What omega family does oleic acid belong to?

Omega-9

Why do fatty acids within the same omega family differ?

They may have different chain lengths and numbers of double bonds, but the closest double bond to the methyl end is in the same position.

What defines a saturated fatty acid?

A fatty acid with no carbon–carbon double bonds.

What is butyric acid?

A 4-carbon saturated fatty acid found in butterfat.

What is caproic acid?

A 6-carbon saturated fatty acid found in butterfat.

What is caprylic acid?

An 8-carbon saturated fatty acid found in coconut oil.

What is capric acid?

A 10-carbon saturated fatty acid found in palm oil.

What is lauric acid?

A 12-carbon saturated fatty acid found in coconut oil and palm oil.

What is myristic acid?

A 14-carbon saturated fatty acid found in coconut oil and palm oil.

What is palmitic acid?

A 16-carbon saturated fatty acid found in palm oil.

What is stearic acid?

An 18-carbon saturated fatty acid found in most animal fats.

What is arachidic acid?

A 20-carbon saturated fatty acid found in peanut oil.

What is behenic acid?

A 22-carbon saturated fatty acid found in seeds.

What is lignoceric acid?

A 24-carbon saturated fatty acid found in peanut oil.

Which saturated fatty acids are commonly found in coconut oil?

Caprylic (8), lauric (12), and myristic (14) acids.

Which saturated fatty acids are commonly found in butterfat?

Butyric (4) and caproic (6) acids.

Which saturated fatty acids are found in peanut oil?

Arachidic (20) and lignoceric (24) acids.

What defines an unsaturated fatty acid?

A fatty acid containing one or more carbon–carbon double bonds.

What is palmitoleic acid?

A 16-carbon monounsaturated fatty acid found in seafood and beef.

What is the standard notation and omega notation for palmitoleic acid?

16:1;9 and 16:1ω7

What is oleic acid?

An 18-carbon monounsaturated fatty acid abundant in olive oil and canola oil.

What is the standard notation and omega notation for oleic acid?

18:1;9 and 18:1ω9

What is linoleic acid with two bonds?

An 18-carbon polyunsaturated fatty acid with two double bonds found in sunflower and safflower oils.

What is the standard notation and omega notation for linoleic acid?

18:2;9,12 and 18:2ω6

What is linolenic acid with three bonds?

An 18-carbon polyunsaturated fatty acid with three double bonds found in soybean and canola oils.

What is the standard notation and omega notation for linoleic acid with two bonds?

18:2;9,12 and 18:2ω6

What is the standard notation and omega notation for linolenic acid with three bonds?

18:3;9,12,15 and 18:3ω3

What is arachidonic acid?

A 20-carbon polyunsaturated fatty acid with four double bonds found in eggs and most animal fats.

What is the standard notation and omega notation for arachidonic acid?

20:4;5,8,11,14 and 20:4ω6

What is eicosapentaenoic acid (EPA)?

A 20-carbon omega-3 polyunsaturated fatty acid with five double bonds found in seafood.

What is the standard notation and omega notation for EPA?

0:5;5,8,11,14,17 and 20:5ω3

What is docosahexaenoic acid (DHA)?

A long-chain omega-3 polyunsaturated fatty acid found in seafood

What is the standard notation and omega notation for DHA?

22:6;4,7,10,13,16,19 and 22:6ω3

Which unsaturated fatty acids are omega-3 fatty acids?

Linolenic acid (three bonds), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

Which unsaturated fatty acids are omega-6 fatty acids?

Linoleic acid (two bonds) and arachidonic acid.

Which unsaturated fatty acid is the most common monounsaturated fat in the diet?

Oleic acid

Omega

the last letter of the Greek alphabet (ω), used by chemists to refer to the position of the closest double bond to the methyl end of a fatty acid.

Do fatty acids usually occur free in foods or the body?

No. They are usually incorporated into triglycerides.

What is a triglyceride?

A lipid composed of three fatty acids attached to one glycerol molecule.

What is glycerol?

A three-carbon molecule that forms the backbone of triglycerides.

What functional groups are attached to glycerol when it is free?

An OH (hydroxyl) group is attached to each carbon.

What happens to glycerol’s OH groups when it forms a triglyceride?

Each OH group is replaced by a fatty acid.

How are triglycerides formed?

Through a series of condensation reactions between glycerol and fatty acids.

What is a condensation reaction?

A chemical reaction in which two molecules bond together and release water.

What components combine to form water during triglyceride formation?

A hydrogen (H) from glycerol and a hydroxyl group (OH) from a fatty acid.

How many water molecules are released when one triglyceride is formed?

Three water molecules.

How many fatty acids attach to glycerol to form a triglyceride?

Three fatty acids.

What type of bond forms between glycerol and fatty acids in a triglyceride?

A bond formed by condensation after water is released.

Are triglycerides usually made of only one type of fatty acid?

No. Most triglycerides contain a mixture of different fatty acids.