The document discusses the structure and function of various lipids, particularly phospholipids, sphingolipids, and cholesterol, crucial components of cell membranes. It details the characteristics of glycerophospholipids and sphingophospholipids, including their polar and nonpolar regions, and their roles as emulsifiers and within brain tissues. Cholesterol's significance as a steroid and its relationship to cardiovascular health is also highlighted, addressing the effects of dietary intake on blood cholesterol levels.

1. LIPIDS
Gemalyn B. Ingaran
Instructor

3. All cells are surrounded by a membrane that confines their contents.
Up to 80% of the mass of a cell membrane can be lipid materials; the rest is
primarily protein. It is membranes that give cells their individuality by
separating them from their environment.

4. 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 platform molecule on which
a phospholipid is built may be the 3-carbon alcohol glycerol or a
more complex C18 aminodialcohol called sphingosine.
Glycerol-based phospholipids are called glycerophospholipids, and
those based on sphingosine are called sphingophospholipids

5. The general block diagrams for a glycerophospholipid
and a sphingophospholipid are as follows:

7. A glycerophospholipid is a lipid that contains two fatty acids
and a phosphate group esterified to a glycerol molecule and an
alcohol esterified to the phosphate group.
All attachments (bonds) between groups in a glycerophospholipid
are ester linkages, a situation similar to that in triacylglycerols.

8. Because of the ester linkages present, glycerophospholipids
undergo hydrolysis and saponification reactions in a manner similar
to that for triacylglycerols. There will be five reaction products,
however, instead of the four for triacylglycerols.

9. Phosphoric acid is the parent source for the minus one charged
phosphate group used in the formation of glycerophospholipids.
The structures of these two entities are

10. The alcohol attached to the phosphate group in a
glycerophospholipid is usually one of three amino alcohols: choline,
ethanolamine, or serine.
The structures of these three amino alcohols, given in terms of the
charged forms that they adopt in neutral solution, are:

11. Eg.: Structural formula for the glycerophospholipid that produces, upon
hydrolysis, equimolar amounts of glycerol, phosphoric acid, and
ethanolamine, and twice that molar amount of stearic acid, the 18:0 fatty
acid.

14. There are two important things to notice about this model:
(1) There is a “head” part, the choline and phosphate and (2)
there are two “tails,” the two fatty acid carbon chains. The
head part is polar. The two tails, the carbon chains, are
nonpolar.

15. • Egg yolks and soybeans are good dietary sources of these lipids.
Within the body, phosphatidylcholines (lecithins) are prevalent
in cell membranes.
• Mayonnaise, ice cream, and custards are some of the products
they are found in. It is the polar–nonpolar (head–tail) structure of
phosphatidylcholines that enables them to function as
emulsifiers.
• Phosphatidylethanolamines and phosphatidylserines are also
known as cephalins. These compounds are found in heart and
liver tissue and in high concentrations in the brain. They are
important in blood clotting.

16. ACTIVITY 6
Draw the structure formula for the
glycerophospholipid that produces,
upon hydrolysis, equimolar amounts of
glycerol, phosphoric acid, and choline,
and twice that molar amount of lauric
acid, the 12:0 fatty acid.

17. SPHINGOPHOSPHOLIPIDS

18. SPHINGOPHOSPHOLIPIDS
SPHINGOPHOSPHOLIPIDS have structures based on
the 18-carbon monounsaturated aminodialcohol
sphingosine.
A sphingophospholipid is a lipid that contains one
fatty acid and one phosphate group attached to a
sphingosine molecule and an alcohol attached to the
phosphate group.

19. SPHINGOPHOSPHOLIPIDS
All phospholipids derived from sphingosine have (1) the fatty
acid attached to the sphingosine -NH2 group via an amide linkage (2)
the phosphate group attached to the sphingosine terminal -OH
group via an ester linkage and (3) an additional alcohol esterified to
the phosphate group.

20. SPHINGOPHOSPHOLIPIDS
The structure of sphingosine, the platform molecule for a
sphingophospholipid:

21. SPHINGOPHOSPHOLIPIDS

22. SPHINGOPHOSPHOLIPIDS
• Like glycerophospholipids, sphingophospholipids
participate in hydrolysis and saponification reactions.
• Sphingophospholipids in which the alcohol esterified
to the phosphate group is choline are called
sphingomyelins. Sphingomyelins are found in all cell
membranes and are important structural components
of the myelin sheath, the protective and insulating
coating that surrounds nerves.

23. SPHINGOPHOSPHOLIPIDS
The structural formula for a sphingomyelin in which stearic acid
(18:0) is the fatty acid is

24. MEMBRANE
LIPIDS:
SPHINGOGLYCOLIPIDS

25. SPHINGOGLYCOLIPIDS
A SPHINGOGLYCOLIPID is a lipid that contains both a fatty acid
and a carbohydrate component attached to a sphingosine molecule. A
fatty acid is attached to the sphingosine through an amide linkage,
and a monosaccharide or oligosaccharide is attached to the
sphingosine at the terminal -OH carbon atom through a glycosidic
linkage.

26. SPHINGOGLYCOLIPIDS
Like glycerophospholipids and sphingophospholipids,
sphingoglycolipids have a “head and two tail” structure.
Sphingoglycolipids and sphingophospholipids have similar
“tails,” but their polar “heads” differ in the constituents
present (mono- or oligosaccharide versus phosphate-
alcohol).

27. SPHINGOCLYCOLIPIDS
The simplest sphingoglycolipids, which are called cerebrosides, contain a single
monosaccharide unit—either glucose or galactose. As the name suggests, cerebrosides
occur primarily in the brain (7% of dry mass). They are also present in the myelin sheath of
nerves. The specific structure for a cerebroside in which stearic acid (18:0) is the fatty acid
and galactose is the monosaccharide is:

28. SPHINGOCLYCOLIPIDS
More complex sphingoglycolipids, called gangliosides,
contain a branched chain of up to seven monosaccharide
residues. These substances occur in the gray matter of the
brain as well as in the myelin sheath.

29. Terminology for and Structural Relationships Among Various Types of Fatty-Acid-Containing Lipids

30. MEMBRANE
LIPIDS:
CHOLESTEROL

31. CHOLESTEROL
Cholesterol is a steroid. 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, which is
called the steroid nucleus, has the following structure:

32. CHOLESTEROL
Remember:
Cholesterol’s structure differs markedly from
that of other membrane lipids in that
(1)There are no fatty acid residues present
and;
(2)Neither glycerol nor sphingosine is
present as the platform molecule.

33. 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.
The -ol ending in the name cholesterol
conveys the information that an alcohol
functional group is present in this molecule; it is
located on carbon 3 of the steroid nucleus.

34. CHOLESTEROL

35. CHOLESTEROL
Within the human body, cholesterol is found in cell
membranes (up to 25% by mass), in nerve tissue, in
brain tissue (about 10% by dry mass), and in virtually
all fluids. Every 100 mL of human blood plasma
contains about 50 mg of free cholesterol and about
170 mg of cholesterol esterified with various fatty
acids

36. CHOLESTEROL
• Although a portion of the body’s cholesterol is obtained
from dietary intake, most of it is biosynthesized by the
liver and (to a lesser extent) the intestine.
• Typically, 800–1000 mg are biosynthesized each day.
Ingested cholesterol decreases biosynthetic cholesterol
production.
• However, the reduction is less than the amount ingested.
Therefore, total body cholesterol levels increase with
increased dietary intake of cholesterol.

37. CHOLESTEROL
• The lipoproteins that carry cholesterol from the liver to various
tissues are called LDLs (low-density lipoproteins), and those
that carry excess cholesterol from tissues back to the liver are
called HDLs (high-density lipoproteins). If too much cholesterol
is being transported by LDLs or too little by HDLs, the imbalance
results in an increase in blood cholesterol levels.
• High blood cholesterol levels contribute to atherosclerosis, a
form of cardiovascular disease characterized by the buildup of
plaque along the inner walls of arteries.

38. CHOLESTEROL
Plaque is a mound of lipid
material mixed with smooth
muscles and and calcium.
Plaque deposits in the arteries
that serve the heart reduce
blood flow to the heart
muscle and can lead to a
heart attack.

39. CHOLESTEROL
People who want to reduce
dietary cholesterol intake
should reduce the amount
of animal products they eat
(meat, dairy products, etc.)
and eat more fruit and
vegetables. Plant foods
contain negligible amounts
of cholesterol; cholesterol
is found primarily in foods
of animal origin.

40. CHOLESTEROL
• The cholesterol associated with LDLs is often called “bad
cholesterol” because it can contribute to increased blood
cholesterol levels.
• The cholesterol associated with HDLs is often called “good
cholesterol” because it reduced blood cholesterol levels.