Dietary lipids consist mainly of triacylglycerols which provide energy. Fatty acids are hydrophobic molecules that can be saturated or unsaturated. Saturated fatty acids pack tightly and have higher melting points, making them more solid at room temperature. Unsaturated fatty acids have kinks that prevent tight packing and have lower melting points. Triglycerides store fatty acids as an efficient energy source. Phospholipids are polar lipids that form bilayers, which act as barriers in cell membranes. Some lipids function as signals, cofactors, or pigments and play important roles in cell processes.

1. Dietary Lipids
Metabolism

3. The average daily intake
of lipids by U.S. adults is
which
about 81 g, of
more than 90% is
normally triacylglycerol
(TAG ‫الشحوم‬
‫الثالثية‬ ). The
remainder of the dietary
lipids consists primarily
of
cholesterol, cholesteryl
esters, phospholipids,
and unesterified (“free”)
fatty acids.

8. Defined on the basis of solubility.
Lipids: heterogeneous group of water insoluble
(hydrophobic) organic molecules,
they are chemically diverse compound but
have one feature: water insoluble
Many distinct chemical species in a “lipid fraction”
Lipids

9. Functions
-The biological functions of lipids are diverse as their chemistry Lipids perform
three biological functions:
1. Lipids in form of a bilayer are essential
components of biological membranes.
2. Lipids containing hydrocarbon
side chains serve as energy stores.
3. Many intra-and intercellular signaling events involve lipid molecules.

10. 1. Storage lipids
Triglycerides, Waxes and Fatty acids.
s.
Fats and oils are stored forms of energy and are derivatives of fatty acid
2. Structural lipids in membranes
Glycerophospholipids, Sphingolipids, Sterols.
are major structural elements in biological membranes
3. Lipids as signals, cofactors and pigments.
These lipids presents in small quantities but play crucial roles
-Phosphatidylinositols, Eicosanoids
- Prostaglandins.
- Thromboxanes.
- Leukotrienes.
- Steroid hormones carry messages between tissues.
- Vitamins A and D are hormone precursors.
- Vitamins E and K are oxidation-reduction cofactors.
Lipid Classification
Triglycerides
Common lipid signaling molecules:
lysophosphatidic acid (LPA)
sphingosine-1-phosphate (S1P)
platelet activating factor (PAF)
anandamide or arachidonoyl ethanolamine (AEA)

11. Fats and oils are derivatives of Fatty acids.
Fatty acids (F.A) are carboxylic acids with long
hydrocarbon chain ranging from 4-36 carbon atom
16- and 18-C long are most abundant.
-Even number of carbons, 16, 18… the odd are also
present but rare.
- the hydrocarbon chain can be fully saturated
(without double bonds), or with one, two or three
double bonds (cis-configuration only)
-usually they are unbranched, some cases have
methyl, hydroxyl, or three-carbon ring as branch

12. The nomenclature of these acids is rather complicated. There are at least five
systems in use.
Here are some of the above in the different systems:
1The delta system numbers the double bonds from the carboxyl group (the α
carbon), specify the chain length and the number of
double bonds separated by colon
Palmitic acid is saturated F. A with 16 C atoms  16:0
Stearic acid  18:0
2 whereas the omega system indicates where
the first double bond is counting
from the other end of the molecule
(the methyl group, the ω carbon).
Nomenclature
Linoleic acid  18:2( 9,12)
Arachodonic acids 20:4 ( 5,8,11,14)

13. Omega Fatty acids
-Essential F.A
Linoleic (18:29,12)
6
Linolenic (18:39,12,15)
3
Arachidonic (20:45,8,11,14)
6

14. The position of double bond should be specified superscript numbers
following the  (delta)
Oleic acid  18:1(9)
Linoleic acid  18:2( 9,12)
1
9
Linolenic acid  18:3( 9,12,15)
the location of double bonds is 9=10; 12=13; 15=16
Arachidonic acids 20:4 ( 5,8,11,14)
-the polyunsaturated F. A are never conjugated, the double bond is
separated by methyl group

15. Molecular structure Name
Lauric acid: saturated C12
Myristic acid: saturated C14
Palmitic acid: saturated C16
Stearic acid: saturated C18
Oleic acid: monounsaturated C18
Linoleic acid: diunsaturated C18
γ-Linolenic acid: triunsaturated C18
Arachidonic acid: tetraunsaturated C20

17. Longer the fatty acid chain -Higher the melting temperature
( i.e. more solid at room temp)
More double bonds -lower the melting temperature
( i.e. more liquid at room temperature )

18. Essential fatty acids
Two fatty acids are dietary essentials in humans because of
our inability to synthesize them: linoleic acid, which is the
precursor of arachidonic acid, the substrate for prostaglandin
synthesis, and α-linolenic acid, the precursor of other fatty
acids important for growth and development. Plants provide
us with the essential fatty acids. [Note: Arachidonic acid
becomes essential if linoleic acid is deficient in the diet.]

19. Physical properties of F. A and the compounds containing them are largely determined
by the length and degree of unsaturation of the hydrocarbon chain.
Solubility: The non-polar hydrocarbon chain account for the poor solubility of F. A in
water
Lauric acid 12:0 Molecular Weight (M. wt) 200 sol. In water 0.063 mg/g
Glucose Molecular Weight (M. wt) 180  water sol. Is 1.1mg/g
*The carboxyl group is polar and this accounts for the slight solubility of short chai
fatty acid in water
*The longer the fatty acid acyl and fewer the double bonds, the lower is the
solubility in water
Melting points
melting points are strongly influenced by the length and degree of unsaturation
at room tem. (R.T) the saturated F. A with length chain 12-24 have waxy consistency
while the unsaturated F. A are liquid
Physical properties of fatty acids

20. fully saturated molecule 
free rotation around each C-C
This gives the hydrocarbon
chain great freedom and
flexibility
 adopt the most stable
conformation which is the
fully extended form in which
the steric hindrance of
neighboring atoms is minimized
The molecules can pack together
tightly in nearly crystalline arrays.
So the Vander Waal interaction
and the hydrophobic interaction
are maximized
High thermal energy required to
disorder (melt) these highly
ordered F.A molecules  higher
melting points
Saturated chains pack
tightly and form more
rigid, organized
aggregates

21. In the unsaturated F. A
the cis configuration
double bond forces a kink
(bend) in the hydrocarbon
chain
Unsaturated chains bend
and pack in a less ordered
way, with greater potential
for motion
F.A with one or more kinks cannot
pack together as tightly as fully
saturated F.A and their
interactions are weaker
So the unsaturated F.As take
less thermal energy to disorder
these poorly ordered arrays of
unsaturated F.As  they have
lower melting points

22. Waxy (Fat) Liquid (Oil)
The saturated F.As take high
thermal energy required to disorder
(melt) these highly ordered F.A
molecules  higher melting points
The unsaturated F.As take less
thermal energy to disorder these
poorly ordered arrays of
unsaturated F.As  they have
lower melting points

23. Storage of fatty acids as components of triacylglycerols
Mono-, di-, and triacylglycerols consist of one, two, or three
molecules of fatty acid esterified to a molecule of glycerol.
Fatty acids are esterified through their carboxyl groups,
resulting in a loss of negative charge and formation of
“neutral fat.” [Note: If a species of acylglycerol is solid at room
temperature, it is called a “fat”; if liquid, it is called an “oil.”]

24. Triacylglycerols or Triglycerides
Fatty acid triesters of glycerol Most contain two or
three different types of fatty acid residues.
triglycerides are non-polar and hydrophobic
molecules (the polar groups of both glycerol
and F. A are linked in ester linkage  non-
polar molecule )
Simple triacylglycerols: containing the same
kind of F.A in all three positions of glycerol
Simple triacylglycerols of
18:0 = tristearin
16:0 tripalmitin
18:1 triolein
Mixed triacylglycerols: different fatty acids
esterified with glycerol

25. Glycerol:
Lipid: Glycerol + 2 or 3 Fatty Acids
•Di-glycerides are mostly plant oils & waxes
•Tri-glycerides are mostly animal fats
(FattyAcids= Carbon Chains)

26. Fats and oils
* Plant oils are usually richer in unsaturated fatty acids
residues than animal fats
*Fats and oils are complex mixtures of mixed triacylglycerols
and simple triacylglycerols
*Triacylglycerols can be found in most eukaryotic cell as oily
droplets in the aqueous cytosol serving as metabolic fuel
*In vertebrates specialized cells called Adipocytes (fat cell)
store amounts of triglycerides as fat droplets that fill the cell.
Triglycerides also stored as oil in the seeds of many types of
plants .
*Adipocytes contain lipases catalysis the hydrolysis of stored
triglycerides releasing F.A for export to sites where they can
be used as fuel.

27. *Two advantages for using the triglycerides as
stored fuel rather than polysaccharides as
glycogen and starch:
1the carbon atoms of F.A are more reduced than
that of carbohydrates  oxidation of triglycerides
yields more than twice as much energy (gm/gm) as
the oxidation of CHO (F.A  9 Kcal, CHO  4 Kcal).
2triglycerides are hydrophobic unhydrated, the
organism that carries fat as fuel does not have to
carry the extra weight of water of hydration that is
associated with stored polysaccharides (2gm
water/1gm polysaccharides).

28. Fats function as energy reservoirs in animals
The fat content of normal humans allows them to
survive starvation for 2 or 3 months.
While human store of glycogen can supply only for
one day, but carbohydrates are quick sources for
metabolic energy because of water solubility.
Fat stores: skin, abdominal cavity and mammary gland
Triacylglycerols.
Triacylglycerols function to insulate: protect the
body from the outer environments

29. Vegetable oils: are composed of Triacylglycerols with
unsaturated fatty acids  liquid at room temp.
Vegetable oils can be into solid by catalytic hydrogenation
which reduce the double bonds to single bonds.

30. Exposure of the lipid rich food to oxygen for long time  may spoil and
the lipid is said to be Rancid.
Rancidity results from the cleavage of double bond in unsaturated F. A
that produce aldehyde and carboxylic acid with low M.wt  bad smell

31. Waxes serve as energy store and water repellents
Biological waxes are esters of
•long chain (C14-C36) saturated and unsaturated fatty acid
•with long chain alcohol (C16-C30)
•melting points about 60-100 ºC
C14-C36 sat. & unsat. F.A C16-C30 long chain alcohol
Function of Biological waxes
-Skin glands of some vertebrates secret waxes to protect hair and
skin to keep it pliable, lubricated and water proof
-Leaves of many tropical plants are coated by waxes to prevent
excessive evaporation of water and protect against parasites
-Waxes can be used in pharmaceutical industries in lotions,
ointments and polishes

32. Polar vs. Nonpolar lipids
•Non-Polar Lipids –Energy storage
•Polar lipids are the basis of Bilayers
Biological membranes
feature: double layer of lipid
act as barrier to the passage
of polar molecules and ions.
Amphipathic: one end of the
molecule is hydrophobic and
the other is hydrophilic
The hydrophobic interactions
between molecules and the
hydrophilic interactions with
water direct their packing into
sheets called membrane bilayer

33. • Group of lipids present in small amounts
play various essential function
- Have active roles in metabolic processes
as metabolite and messenger
- Potent signals and hormones carried in the
blood from one tissue to others
- Intracellular messengers generated to
response to outer signal
- Can function as cofactors
- Pigments
- Fat soluble vitamins

34. OVERVIEW OF PHOSPHOLIPIDS
Phospholipids are polar, ionic compounds composed of an
alcohol that is attached by a phosphodiester bridge to either
diacylglycerol or sphingosine. Like fatty acids, phospholipids
are amphipathic in nature, that is, each has a hydrophilic head
(the phosphate group plus whatever alcohol is attached to it,
for example, serine, ethanolamine, and choline, and a long,
hydrophobic tail (containing fatty acids or fatty acid–derived
hydrocarbons.

35. • Phospholipids are the predominant lipids of cell
membranes. In membranes, the hydrophobic portion of
a phospholipid molecule is associated with the nonpolar
portions of other membrane constituents, such as
glycolipids, proteins, and cholesterol. The hydrophilic
(polar) head of the phospholipid extends outward,
interacting with the intracellular or extracellular aqueous
environment. Membrane phospholipids also function as
a reservoir for intracellular messengers, and, for some
proteins, phospholipids serve as anchors to cell
membranes. Nonmembrane-bound phospholipids serve
additional functions in the body, for example, as
components of lung surfactant and essential components
of bile, where their detergent properties aid in the
solubilization of cholesterol.

36. STRUCTURE OF PHOSPHOLIPIDS
There are two classes of phospholipids:
those that have glycerol as a backbone and
those that contain sphingosine. Both classes
are found as structural components of
membranes, and both play a role in the
generation of lipid-signaling molecules.

37. A- Glycerophospholipids (Phospholipids)
Phospholipids that contain glycerol are called glycerophospholipids
(or phosphoglycerides). Glycerophospholipids constitute the major
class of phospholipids.All contain (or are derivatives of) phosphatidic
acid (diacylglycerol with a phosphate group on the third carbon,
Figure 17.1B). Phosphatidic acid is the simplest phosphoglyceride,
and is the precursor of the other members of this group.

38. 1- Glycerophospholipids are formed from phosphatidic acid (PA)
and an alcohol: The phosphate group on PAcan be esterified to
another compound containing an alcohol group For example:
Serine + PA→ phosphatidylserine
Ethanolamine + PA→ phosphatidylethanolamine (cephalin(
Choline + PA→ phosphatidylcholine (lecithin(
Inositol + PA→ phosphatidylinositol
Glycerol + PA→ phosphatidylglycerol

39. Lipids as Signals, cofactors and pigments
Intracellular messengers are released
from the Phosphotidyl inositol in response
to extra cellular signals interacting with
receptors on the outer surface of the
membrane.
* Signals act through a series of steps
Phosphatidyl inositol:
act as intracellular signals:

40. IP3

42. *some animal tissues are rich in ether lipids: one of the acyl group is
attached to glycerol in ether rather than ester linkage. The ether-
linked chain can be saturated alkyl ether lipid or may unsaturated
alkene-ether linked chain
3- Platelet activating factor: released from leukocyte (basophiles) and
stimulate platelet aggregation and the release of serotonin
2- Plasmalogen: ether linked alkene found in heart tissue, 50% of the
phosphlipid in the heart is Plasmalogen

43. B- Sphingolipids
Sphingolipids are major membrane components, with polar head and non-polar tail
• They are derivatives of the C18 amino alcohol sphingosine
• The double bond in sphingosine is trans
•C1, C2, C3 of sphingosine molecule are structurally similar to the three carbons of
glycerol in phospholipids
• N-acyl fatty acid derivatives of sphingosine are known as ceramides
• Ceramides are the parent compounds of the more abundant sphingolipids.
General structure of Sphingolipids, if X is H, the
compound is Ceramide

45. Sphingomyelins: contain phosphocholine or phosphoethanolamine as their
polar group and so can be classified as phospholipids.
Sphingomyelins resemble phosphotidylcholines in their general properties
and three-dimensional structure and in having no net charge on their head
groups
The myelin sheath that surrounds and insulates nerve cells is rich in
Sphingomyelins

46. Glycosphingolipids (Glycolipids): occur largely in the outer
face of plasma membrane, have one or more sugars connected
directly to the –OH at C1 of the ceramide moiety and can be
classified
A- Neutral Glycolipids (uncharged) no net charge at pH=7
1 Cerebroside: single sugar linked to ceramide usually Glucose
or Galactose
2Globoside: Di, tri or tetrasaccharide linked to ceramide as
Glu, Gal, N-acetly galactosamine

47. B- Ganglioside: the most complex glycolipid, have
oligosaccharide as their polar head groups and one or more
residues of Sialic acid
Ganglioside are primarily components of membranes on cell
surfaces and constitute 6% of brain lipids
Sphingolipids: act as a site of biological recognition, act as
receptors for hormones and glycoproteins

48. VIII. PROSTAGLANDINS AND RELATED COMPOUNDS
Prostaglandins, and the related compounds thromboxanes and
leukotrienes, are collectively known as eicosanoids to reflect their origin
from polyunsaturated fatty acids with 20 carbons. They are extremely
potent compounds that elicit a wide range of responses, both physiologic
(inflammatory response) and pathologic (hyper -sensitivity). They ensure
gastric integrity and renal function, regulate smooth muscle contraction
(intestine and uterus are key sites) and blood vessel diameter, and
maintain platelet homeostasis. Although they have been compared to
hormones in terms of their actions, eicosanoids differ from the true
hormones in that they are produced in very small amounts in almost all
tissues rather than in specialized glands. They also act locally rather than
after transport in the blood to distant sites, as occurs with true hormones
such as insulin. Eicosanoids are not stored, and they have an extremely
short half-life, being rapidly metabolized to inactive products. Their
biologic actions are mediated by plasma membrane G protein–coupled
receptors, which are different in different organ systems.

49. Eicosanoids:
Eicosanoids are derived from membrane lipids and mainly from
Arachodonic acid [20:4(5,8,11,14 ]
1- Prostaglandins
•C20 compounds
• Five carbon ring
• affect a wide range of cellular and tissue function
•Act at low concentration and are involved in the production of pain and
fever, regulation of blood pressure, blood coagulation and reproduction
•Produced and used locally
• Regulate the synthesis of the intracellular messenger (cAMP) which
mediate the action of different hormones.
-Stimulate the contraction of smooth muscle in the uterus.
-Affect the blood flow
-Elevate the body temperature and mediate the inflammation and pain

50. 2 Thromboxanes:
Six-memebred ring containing an ether, produced by
the platelets (thrombocytes) and play role in
formation of the blood clots
3Leukotriens: contain conjugated double bonds,
found in the leukocytes, powerful biological signals,
induce contraction of muscles lining the airways of
the lung. Over production cause asthmatic attack

53. NSAIDs and Aspirin
Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and
derivatives of ibuprofen and acetaminophen, inhibit Cyclooxygenase activity
of PGH2 Synthase, by non covalently binding to PGH2 synthase, also
preventing arachidonic acid from reaching the enzyme active site.
They inhibit formation of prostaglandins involved in fever, pain and
inflammation. They inhibit blood clotting by blocking thromboxane formation
in blood platelets.
Aspirin acetylates a serine hydroxyl group residue of the enzyme PGH2
synthase (Cyclo oxygenase enzyme) near the active site, preventing
arachidonic acid from reaching the enzyme active site. The inhibition by
aspirin is irreversible.

54. Leukotrienes have been implicated in various inflammatory and
hypersensitivity disorders (such as asthma). They are
synthesized from arachidonate by an aspirin-insensitive
pathway
However, in most body cells re-synthesis of PGH2 Synthase
would restore cyclooxygenase activity.
Steroidal anti-inflammatory drug
Prednisone and prednisolone inhibit the phospholipase A2 that
release the Arachodinic acid from the phospholipids in the
membrane  the synthesis of all eicosanoid will be inhibited

55. 3-Sterols
Structural lipids present in the membranes of some
eukaryotic cells. Characterized by the steroid
nucleus consisting of four fused rings three rings
with 6 C atoms and one ring with 5 C atoms, the
steroid nucleus is relatively rigid and planar.
Cholesterol is the major sterol in animal tissues and
it is amphipathic with a polar head (the –OH group),
and the non-polar body is the steroid nucleus
Similar sterols are present in eukaryotes:
Stigmasterol plants
Ergosterol fungi
Functions
- Membrane constituents
- Precursors of different product with vital biological activities (steroidal
hormones that regulate the gene expression)
- Bile acids are derivatives of cholesterol that act as emulsifying agent in
the intestine

56. STEROID HORMONES
Cholesterol is the precursor of all
classes of steroid hormones:
glucocorticoids (for example,
cortisol), mineralocorticoids (for
example, aldosterone), and sex
hormones—androgens, estrogens,
and progestins. [Note:
Glucocorticoids and
mineralocorticoids are collectively
called corticosteroids.]
Synthesis and secretion occur in the
adrenal cortex (cortisol,
aldosterone, and androgens),
ovaries and placenta (estrogens and
progestins), and testes
(testosterone)

57. Steroidal Hormones
Steroids: oxidized form of the
sterol, with the steroid nucleus
but lack the alkyl chain
-More polar than cholesterol
-Move through the blood on
proteins carriers from site of
production to target tissue.
Then bind to their receptors 
enter the nucleus  affect the
gene expression and metabolism
-male and female sex hormones
(Testosterone and estradiaol)
-adrenal cortex hormone:
cortisol and aldesterone
-Prednisone and prednisolone
are synthetic steroids

58. Lipid Soluble Vitamins
Vitamins: Compounds that are essential to the health of human
and other animals
most of the vitamins cannot be synthesized by endogenously
Two classes of Vitamins
a. Fat soluble vitamins
b. Water soluble vitamin, Vit B and Vit C

59. Vitamin D
A group of structurally related compounds that play a role in the regulation of
calcium and phosphorus metabolism
-the most abundant form in the circulatory system is vitamin D3
(Cholecalciferol) which is formed in the skin from 7-dehydrocholesterol
-Vit D3 is converted into the active form in two steps:
 the first at the liver
 and the second at the kidney
-The active form of vit D3 (1,25-dihydroxycholecalciferol) regulates the Ca
uptake in the intestine and Ca levels in the kidney
-Deficiency of Vit D3  defective bone formation and Rickets disease

60. Vitamin D activation

61. Vitamin A (Retinol)
•Vit A with its precursors and its derivatives function
as hormones and as the visual pigments in the eye
• An antioxidant
•β-carotene: yellow pigments in the carrot
Retinoic acid : is a derivative of Vit A and can
regulate gene expression in the development of
epithelial tissue (skin)

62. Vitamin E
•Vitamin E is a group of compounds of similar structure; the most
active is α-tocopherol
- Associates with cell membranes, lipids, lipoproteins in the blood
-An antioxidant; traps HOO• and ROO• radicals formed as a result
of oxidation by O2 of unsaturated hydrocarbon chains in membrane
phospholipids  protect the unsaturated F.A from oxidation and
prevent oxidative damage to membrane lipid
-Deficiency of Vit. E : Rough skin, muscular weakness and sterility

63. •Blood clot factor: undergo a cycle of oxidation reduction during the
formation of the active prothrombine
•Different forms, most common n=8
•Functions in blood clotting
Vitamin K
Vit K1 (Phylloquinone)