This document provides information on lipids, including their classification, functions, and examples. It discusses simple lipids like triglycerides and fatty acids, as well as complex lipids including phospholipids, glycolipids, sterols, and steroids. Specific lipid types and their structures are explained, such as cholesterol, bile acids, eicosanoids like prostaglandins, and steroid hormones. Lipids serve important roles in the body including energy storage, membrane components, and cell signaling.

1. Lipids

2. Lipids
• Are a family of substances that are insoluble in water
but soluble in nonpolar solvents and solvents of low
polarities, such as diethyl ether
• Are naturally occurring molecule from a plant or
animal that is soluble in nonpolar organic solvents.

3. Functions of Lipids
• Storage
• Membrane Components
• Messengers

4. Classification of Lipids
• Simple Lipids
– Triglycerides (Saturated,
monounsaturated,
polyunsaturated)
– Waxes
• Compound Lipids
– Phospholipids
– Glycolipids
• Derived Lipids
– Steroids

5. Triglycerides (Fatty acids)
• Triglycerides are triesters of glycerol
and long-chain carboxylic acids called
fatty acids.
• Fatty acids are long, unbranched
hydrocarbon chains with a carboxylic
acid group at one end. Most have even
numbers of carbon atoms. Fatty acids
may or may not contain carbon-carbon
double bonds. Those without double
bonds are known as saturated fatty
acids; those with double bonds are
known as unsaturated fatty acids.

6. Triglycerides (Fatty acids)
• In contrast to the alcohol part, the acid component of triglycerides may be
any number of fatty acids. These fatty acids do, however, have certain
things in common:
– Fatty acids are practically all unbranched carboxylic acids.
– They range in size from about 10 to 20 carbons.
– They contain an even number of carbon atoms.
– Apart from the -COOH group, they have no functional groups, except that some
do have double bonds.
– In most fatty acids that have double bonds, the cis isomers predominate.

7. Types of Fatty Acids
• Saturated fatty acid - a fatty acid with a carbon chain in
which all carbon-carbon bonds are single bonds.
• Monounsaturated fatty acid - a fatty acid with a carbon chain
in which one carbon-carbon double bond is present.
• Polyunsaturated fatty acid - a fatty acid with a carbon chain
in which two or more carbon-carbon double bonds are
present.

8. Biologically
Important
Fatty acids

9. Fats and Oils
• Fats are naturally occurring mixtures of triacylglycerol molecules in which
many different kinds of triacylglycerol molecules are present. Oils are also
naturally occurring mixtures of triacylglycerol molecules in which there are
many different kinds of triacylglycerol molecules present.
• Fat is a triacylglycerol mixture that is solid or semi-solid at room
temperature (25oC). Generally, fats are obtained from animal sources. Oil is
a triacylglycerol mixture that is a liquid at room temperature (25oC).
Generally, oils are obtained from plant sources

10. Other differences between Fats and
Oils
• Fats are composed largely of
triacylglycerols in which saturated fatty
acids predominate, although some
unsaturated fatty acids are present. Such
triacylglycerols can pack closely together
because of the “linearity” of their fatty acid
chain, thus causing the higher melting
points associated with fats. Oils contain
triacylglycerols with larger amounts of
mono- and polyunsaturated fatty acids
than those in fats. Such triacylglycerols
cannot pack as tightly together because of
“bends” in their fatty acid chains The result
is lower melting points.

11. Other differences between Fats and
Oils
• Fats are generally obtained from animals; hence
the term animal fat. Although fats are solids at room
temperature, the warmer body temperature of the
living animal keeps the fat somewhat liquid (semi-
solid) and thus allows for movement. Oils typically
come from plants, although there are also fish oils.
A fish would have some serious problems if its
triacylglycerols “solidified” when it encountered cold
water.
• Pure fats and pure oils are colorless, odorless, and
tasteless. The tastes, odors, and colors associated
with dietary plant oils are caused by small amounts
of other naturally occurring substances present in
the plant that have been carried along during
processing. The presence of these “other”
compounds is usually considered desirable.

12. Waxes
• Wax is a mixture of fatty acid long-chain
alcohol esters. The acids usually have an even
number from 16 to 36 carbons, whereas the
alcohols have an even number from 24 to 36
carbons. For example, a major component in
beeswax is the ester formed from a 30-carbon
alcohol (triacontanol) and a 16-carbon acid
(palmitic acid).
• The waxy protective coatings on most fruits,
berries, leaves and animal furs have similar
structures. Aquatic birds have a water-
repellent waxy coating on their feathers. When
caught in an oil spill, the waxy coating
dissolves in the oil and the birds lose their
buoyancy.

13. Properties of Triglycerides
Physical Properties
• Water solubility for fatty acids is a direct function of carbon chain length;
solubility decreases as carbon chain length increases. Short-chain fatty
acids have a slight solubility in water. Long-chain fatty acids are essentially
insoluble in water. The slight solubility of short-chain fatty acids is related to
the polarity of the carboxyl group present. In longer-chain fatty acids, the
nonpolar nature of the hydrocarbon chain completely dominates solubility
considerations

14. Properties of Triglycerides
Physical Properties
• Melting points for fatty acids are strongly
influenced by both carbon chain length
and degree of unsaturation (number of
double bonds present). As carbon chain
length increases, melting point
increases. This trend is related to the
greater surface area associated with a
longer carbon chain and to the
increased opportunities that this greater
surface area affords for intermolecular
attractions between fatty acid
molecules.

15. Average Percentage of Fatty Acids of Some
Common Fats and Oils

16. Chemical Reactions of Triglycerides
Hydrogenation
• The carbon-carbon double bonds in vegetable oils can be hydrogenated to
yield saturated fats in the same way that any alkene can react with
hydrogen to yield an alkane

17. Chemical Reactions of Triglycerides
Saponification
• Glycerides, being esters, are subject to hydrolysis, which can be carried out
with either acids or bases. Saponification is a reaction carried out in an
alkaline (basic) solution. For fats and oils, the products of saponification are
glycerol and fatty acid salts.

18. How does soap do its job?
• Soaps work as cleaning agents because the two ends of a soap molecule are so different.
The sodium salt end is ionic and therefore hydrophilic (water-loving); it tends to dissolve in
water. The long hydrocarbon chain portion of the molecule, however, is nonpolar and
therefore hydrophobic (water-fearing). Like an alkane, it tends to avoid water and to
dissolve in nonpolar substances such as grease, fat, and oil. Because of these opposing
tendencies, soap molecules are attracted to both grease and water.

19. How does soap do its job?
• When soap is dispersed in water, the big organic anions cluster together so that their long,
hydrophobic hydrocarbon tails are in contact. By doing so, they avoid disrupting the strong
hydrogen bond interactions of water and instead create a nonpolar microenvironment. At the
same time, their hydrophilic ionic heads on the surface of the cluster stick out into the water.
The resulting spherical clusters are called micelles. Grease and dirt are suspended in water
because they are coated by the nonpolar tails of the soap molecules and trapped in the center
of the micelles. Once suspended within micelles, the grease and dirt can be rinsed away.

20. Phospholipids
• Phospholipids are the most abundant type of membrane lipid. A
phospholipid is a lipid that contains one or more fatty acids, a phosphate
group, a platform molecule to which the fatty acid(s) and the phosphate
group are attached, and an alcohol that is attached to the phosphate group.
• The phospholipids contain a phosphate ester link. They are built up from
either glycerol (to give glycerophospholipids) or from the alcohol
sphingosine (to give sphingomyelins).

21. Glycerophospholipids
• Glycerophospholipids (also known
as phosphoglycerides) are
triesters of glycerol 3-phosphate,
and are the most abundant
membrane lipids. Two of the ester
bonds are with fatty acids, which
provide the two hydrophobic tails.
The fatty acids may be any of the
fatty acids normally present in fats or
oils. The fatty acid acyl group
bonded to C1 of glycerol is usually
saturated, whereas the fatty acyl
group at C2 is usually unsaturated.
At the third position in
glycerophospholipids, there is a
phosphate ester group.

22. Glycerophospholipids

23. Sphingolipids
• Myelin, the coating of nerve axons, contains a different kind of complex lipid: sphingolipids. In
sphingolipids, the alcohol portion is sphingosine
• A long-chain fatty acid is connected to the -NH2 group by an amide bond, and the -OH group at
the end of the chain is esterified by phosphorylcholine:

24. Glycolipids
• Glycolipids, like sphingomyelins, are derived from sphingosine. They differ in having a
carbohydrate group at C1 instead of a phosphate bonded to choline.
• Glycolipids reside in cell membranes with their carbohydrate segments extending into the
fluid surrounding the cells, just as do the carbohydrate segments of glycoproteins.
• The glycolipid molecule is classified as a cerebroside. Cerebrosides, which contain a single
monosaccharide, are particularly abundant in nerve cell membranes in the brain, where the
monosaccharide is D-galactose. They are also found in other cell membranes, where the
sugar unit is D-glucose

25. Steroids
• A steroid is a lipid whose structure is based on a fused ring system that involves three 6-
membered rings and one 5-membered ring. This steroid fused-ring system is called the
steroid nucleus. The third major class of lipids is the steroids, which are compounds
containing the following ring system:
In this structure, three cyclohexane rings (A, B, and C)
are connected in the same way as in phenanthrene; a
fused cyclopentane ring (D) is also present. Steroids are
thus completely different in structure from the lipids
already discussed. Note that they are not necessarily
esters, although some of them are.

26. Cholesterol
• Cholesterol is a C27 steroid molecule that is a
component of cell membranes and a precursor for
other steroid-based lipids. It is the most abundant
steroid in the human body.
• Cholesterol serves as a plasma membrane
component in all animal cells— for example, in red
blood cells. Its second important function is to
serve as a raw material for the synthesis of other
steroids, such as the sex and adrenocorticoid
hormones and bile salts

27. Cholesterol
• Cholesterol, along with fat, is transported by
lipoproteins. Most lipoproteins contain a core of
hydrophobic lipid molecules surrounded by a shell of
hydrophilic molecules such as proteins and
phospholipids. there are four kinds of lipoproteins:
– High-density lipoprotein (HDL) (“good
cholesterol”), which consists of about 33% protein
and about 30% cholesterol
– Low-density lipoprotein (LDL) (“bad
cholesterol”), which contains only 25% protein but
50% cholesterol
– Very-low-density lipoprotein (VLDL), which
mostly carries triglycerides (fats) synthesized by
the liver
– Chylomicrons, which carry dietary lipids
synthesized in the intestines

28. Bile Acids
• An emulsifier is a substance that can disperse and stabilize water-
insoluble substances as colloidal particles in an aqueous solution.
Cholesterol derivatives called bile acids function as emulsifying agents that
facilitate the absorption of dietary lipids in the intestine.
• A bile acid is a cholesterol derivative that functions as a lipid-emulsifying
agent in the aqueous environment of the digestive tract.

29. Bile Acids
• Obtained by oxidation of cholesterol, bile acids
differ structurally from cholesterol in three
respects:
– They are tri- or dihydroxy cholesterol
derivatives.
– The carbon 17 side chain of cholesterol has
been oxidized to a carboxylic acid.
– The oxidized acid side chain is bonded to an
amino acid (either glycine or taurine) through
an amide linkage.

30. Bile Acids
• Bile acids always carry an amino acid
(either glycine or taurine) attached to the
side-chain carboxyl group via an amide
linkage. The presence of this amino acid
attachment increases both the polarity of
the bile acid and its water solubility.
• The medium through which bile acids are
supplied to the small intestine is bile. Bile
is a fluid containing emulsifying agents that
are secreted by the liver, stored in the
gallbladder, and released into the small
intestine during digestion.

31. Cholesterol derivative: Steroid
Hormones
• A hormone is a biochemical substance,
produced by a ductless gland, that has a
messenger function. Hormones serve as a
means of communication between various
tissues. Some hormones, though not all,
are lipids.
• A steroid hormone is a hormone that is a
cholesterol derivative. There are two major
classes of steroid hormones: (1) sex
hormones, which control reproduction and
secondary sex characteristics and (2)
adrenocorticoid hormones, which regulate
numerous biochemical processes in the
body.

32. Sex Hormones
• Sex hormones can be classified into three major groups:
– Estrogens—the female sex hormones
– Androgens—the male sex hormones
– Progestins—the pregnancy hormones

33. Sex Hormones
• Estrogens are synthesized in the ovaries and
adrenal cortex and are responsible for the
development of female secondary sex
characteristics at the onset of puberty and for
regulation of the menstrual cycle. They also
stimulate the development of the mammary
glands during pregnancy and induce estrus (heat)
in animals.
• Androgens are synthesized in the testes and
adrenal cortex and promote the development of
male secondary sex characteristics. They also
promote muscle growth.
• Progestins are synthesized in the ovaries and the
placenta and prepare the lining of the uterus for
implantation of the fertilized ovum. They also
suppress ovulation.

34. Adrenocorticoid Hormones
• The second major group of steroid hormones
consists of the adrenocorticoid hormones.
Produced by the adrenal glands, small organs
located on top of each kidney, at least 28
different hormones have been isolated from
the adrenal cortex (the outer part of the
glands). There are two types of
adrenocorticoid hormones.
– Mineralocorticoids control the balance of
Na+ and K+ ions in cells and body fluids.
– Glucocorticoids control glucose
metabolism and counteract inflammation

35. Eicosanoids
• An eicosanoid is an oxygenated C20 fatty acid derivative that functions as a messenger lipid.
The term eicosanoid is derived from the Greek word eikos, which means “twenty.” The
metabolic precursor for most eicosanoids is arachidonic acid, the 20:4 fatty acid.
• The physiological effects of eicosanoids include the mediation of:
– The inflammatory response,
a normal response to tissue damage
– The production of pain and fever
– The regulation of blood pressure
– The induction of blood clotting
– The control of reproductive functions,
such as the induction of labor
– The regulation of the sleep/wake cycle

36. Prostaglandin
• Prostaglandin is a messenger lipid that is a C20-fatty-acid derivative that contains a
cyclopentane ring and oxygen-containing functional groups. Twenty-carbon fatty acids are
converted into a prostaglandin structure when the eighth and twelfth carbon atoms of the
fatty acid become connected to form a five-membered ring
• Prostaglandins are named after the prostate gland, which was first thought to be their only
source. Today, more than 20 prostaglandins have been discovered in a variety of tissues in
both males and females.
• Within the human body, prostaglandins are involved in many regulatory functions, including
raising body temperature, inhibiting the secretion of gastric juices, increasing the secretion
of a protective mucus layer into the stomach, relaxing and contracting smooth muscle,
directing water and electrolyte balance, intensifying pain, and enhancing inflammation
responses.

37. Thromboxanes
• A thromboxane is a messenger lipid that is a C20-fatty-acid derivative that
contains a cyclic ether ring and oxygen-containing functional groups. As with
prostaglandins, the cyclic structure involves a bond between carbons 8 and
12. An important function of thromboxanes is to promote the formation of
blood clots. Thromboxanes are produced by blood platelets and promote
platelet aggregation.

38. Leukotrienes
• Leukotriene is a messenger lipid that is a C20-fatty-acid derivative that contains three
conjugated double bonds and hydroxy groups. Fatty acids and their derivatives do not
normally contain conjugated double bonds as do leukotrienes Leukotrienes are found in
leukocytes (white blood cells). Their source and the presence of the three conjugated
double bonds account for their name. Various inflammatory and hypersensitivity (allergy)
responses are associated with elevated levels of leukotrienes.

39. Reference and Photo credits
• McMurry,J & Castellion, M.E., Ballantine, D.S., Hoeger, C., Peterson, V.E.
(2010). Essentials of General, Organic and Biological Chemistry (6th
ed.).Pearson Prentice Hall.
• Bettelheim, F.A., Brown, W.H., Campbell, M.K., Farell, S.O. & Torres, O.J.
(2013). Introduction to General, Organic, and Biochemistry (10th ed.).
Cengage Learning. US
• Stoker, S.H (2013). General, Organic, and Biological Chemistry (6th ed.).
Brooks Cole. Cengage Learning. US