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1. Lipid Chemistry
Presented by Dr.
Ibrahim Hassan
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2. Definition
 Lipids are organic compounds containing C,
H, O and are insoluble in water but soluble
in fat solvents (non polar solvents) as
alcohol, ether, benzene and chloroform.
 The lipids are a heterogeneous group of
compounds, including fats, oils, steroids,
waxes, and related compounds, which are
related more by their physical than by their
chemical properties.

3. BIOMEDICAL IMPORTANCE
 They are important dietary constituents due
to high energy value, fat-soluble vitamins
and the essential fatty acids contained in the
fat of natural foods.
 Fat is stored in adipose tissue, where it also
serves as a thermal insulator in the
subcutaneous tissues and around certain
organs.

4. BIOMEDICAL IMPORTANCE cont.,
 Lipoproteins are important, occurring both
in the cell membrane and in the
mitochondria, and serving also as the means
of transporting lipids in the blood.
 Lipid biochemistry is necessary in
understanding many important biomedical
areas, eg, obesity, diabetes mellitus,
atherosclerosis, and the role of various
polyunsaturated fatty acids in nutrition and
health.

5. Lipids
Simple lipids Compound lipids Derived lipids

6. LIPIDS ARE CLASSIFIED AS SIMPLE
OR COMPLEX
 Simple Lipids:
 A- Triglycerides (Neutral fat): esters of fatty
acids with glycerol.
 B- Waxes: esters of fatty acids with long chain
alcohol (higher than glycerol) higher molecular
weight alcohols.
Glycerol: Trihydric alcohol =
3 carbon atoms + 3 (OH) groups

7. FATTY ACIDS ARE ALIPHATIC
CARBOXYLIC ACIDS
 Fatty acids are carboxylic acids with
hydrocarbon straight chains ranging from 4
to 36 carbons long (even number).
 They are two types:
 Saturated (no double bonds)
 Unsaturated (one or more double bonds).

8. Saturated Fatty acids
(no double bonds)
Short chain FA
4-10 carbon atoms
Liquid, volatile
Long chain FA
12-24 carbon atoms
Solid, non volatile

9. Short chain FA
(4-10 carbon atoms) Liquid, volatile
 Butyric acid* (4 C) CH3 - (CH2)2 - COOH
 Caproic acid* (6 C) CH3 - (CH2)4 - COOH
* In certain fats in small amounts (especially butter). An end
product of carbohydrate fermentation by rumen organisms
 Caprylic acid (8 C) CH3 - (CH2)6 - COOH
 Capric acid (10 C) CH3 - (CH2)8 - COOH

10. Long chain FA
(12-24 carbon atoms) Solid, non volatile
 Palmitic acid* (16 C) CH3 - (CH2)14 – COOH
 Stearic acid* (18 C) CH3 - (CH2)16 - COOH
* Common in human and all animal and plant
fats

11. Unsaturated Fatty Acids
(One or More Double Bonds)
CH = CH
Monoethenoid FA
(One double bond)
Polyethenoid FA
(more than one double bond)

12. Unsaturated Fatty Acids
Monoethenoid FA
(One double bond)
 Oleic acid (18 C)
Possibly the most common
fatty acid in natural fats.
Polyethenoid FA
(more than one double bond)
 Diethenoid FA (2 = bonds)
Linoleic acid
Corn, peanut, cottonseed, soybean, and many plant
oils.
 Triethenoid FA (3 = bonds)
Linolenic acid
Some plants, minor fatty acid in
animals.
 Tetraethenoid FA (4 =bonds)
Arachidonic acid
Found in animal fats and in peanut oil; important
component of phospholipids in animals.

13. Essintial Fatty Acids
 Are fatty acids not synthesized in our bodies
and should be supplied in diet.
 Linoleic acid, Linolenic acid and
arachidonic acid are essential FA.
 Arachidonic acid is a precursor of important
group of lipids known as prostglandins.

14. Neutral Fats
Triglycerides - Triacylglycerols
 Are Fatty Acid Esters of Glycerol
 Triacylglycerols are composed of three fatty
acids each in ester linkage with a single
glycerol
Triacylglycerol (TAG)

15. Physical properties
 Insoluble in water
 Soluble in fat solvents
 Colorless, odorless, tasteless
 At RT they are:
 Liquid oil (rich in unsaturated FA)
 Solid fat (rich in saturated FA)

16. Triacylglycerols Provide Stored Energy and Insulation
 In vertebrates, specialized cells called
adipocytes, or fat cells, store large amounts
of triacylglycerols.
 They are also stored as oils in the seeds of
many types of plants.

17. Two advantages of using triacylglycerols as
stored fuels, rather than polysaccharides.
 First, the carbon atoms of fatty acids are
more reduced than those of sugars,
oxidation of triacylglycerols yields more
than twice as much energy, gram for gram,
as the oxidation of carbohydrates.

18. Two advantages of using triacylglycerols as
stored fuels, rather than polysaccharides cont.,
 Second, because triacylglycerols are
hydrophobic and therefore 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 gram (2 g per of
polysaccharide).

19.  Humans have fat tissue (composed
primarily of adipocytes) under the skin, in
the abdominal cavity, and in the mammary
glands.
 In some animals, triacylglycerols stored
under the skin serve not only as energy
stores but as insulation against low
temperatures.

20. Chemical Reactions
 Hydrolysis: by acid or pancreatic lipase yield
glycerol and fatty acids.
Triglycerides → Acid (HCL)→ 3FAs + glycerol
 Saponification: Hydrolysis of fat by alkali to
produce glycerol and soap (salts of FAs)
Triglycerides → Alkali (KOH)→ 3 K soap + glycerol

21. Chemical Reactions
 Hydrogenation (Hardening):
Its addition reaction.
Artifical fat (margrine) formation.
Addition of hydrogen to oils (liquid) at high
temperature in the presence of Nikel as
catalyst results in hydrogenation of
unsaturated FAs with formation of fat (solid).
-CH=CH- →H2 + Nikel + heat → -CH2 – CH2-
Unsat. FA Sat. FA
Oil Solid

22. Chemical Reactions
 Halogenation:
Halogen (I2) can be added at the double
bonds of unsaturated FAs in triglycerides
leading to formation of halogenated saturated
derivatives.
-CH=CH- →I2 → -CH – CH2-
I I
Unsat. FA Sat. FA
Oil Solid

23. Waxes
 They are esters of long-chain
(C14 to C36) saturated and
unsaturated fatty acids with
long-chain (C16 to C30)
alcohols.
 Their melting points (60 to
100 °C) are generally higher
than those of triacylglycerols.
 They are more solid and not
easily hydrolyzed.

24. Compound Lipids
 It is more complicated than simple
lipids as it contains:
FAs
alcohol
Prothetic group

25. Compound
Lipids
Phospholipids Glycolipids Proteolipids

26. Phospholipids
 Are lipids (multiple compounds) containing:
FAs
alcohol
Phosphoric acid
Nitrogen containing bases

27. Phospholipids are the main lipid
constituents of membranes
 Phospholipids may be regarded as derivatives of
phosphatidic acid in which the phosphate is
esterified with the -OH of a suitable alcohol.
 Phosphatidic acid is the precursor of all phospholipids
containing glycerol.
 Hydrolysis = glycerol + Sat. FA
+ Unsat. FA + phosphoric acid

28. Lecithins
(Phosphatidylcholines Occur in Cell Membranes)
 Is present in large amounts in liver and brain.
 Represents a large proportion of the body’s store
of choline. Choline is important in nervous
transmission, as acetylcholine.
 Hydrolysis =
glycerol + Sat. FA
+ Unsat. FA + phosphoric acid
+ choline base

29.  Cobra venom is rich in lecithinase enzyme.
 Lecithinaze removes unsaturated FA from
lecithin converting it into lysolecithin
which causes lyses of RBCs then death 

30. Cephalins
 Are mixture of phophatidyl serine, phosphatidyle
ethanolamine and phosphatidyl inositol.
 Present in liver and brain.
 Phosphatidylinositol Is a Precursor of Second Messengers
 Phosphatidylinositol is an important constituent of cell
membrane phospholipids; upon stimulation by a
suitable hormone, it is cleaved into diacylglycerol and
inositol trisphosphate, both of which act as internal
signals or second messengers.

31. Cardiolipin
 Cardiolipin Is a Major Lipid of
Mitochondrial Membranes
 Present in cardiac tissue.
 Composed of 2 molecules of phosphatidic
acid connected by a molecule of glycerol.
 Hydrolysis = 3 glycerol + 2 sat. FAs
+ 2 unsat. FAs + 2 Phosphoric acid

32. Sphingomyelins
 Sphingomyelins Are Found in the Nervous
System.
 In the myelin sheath of nerve fibers.
 NO glycerol
 Contains long amino alcohol (sphingosine
alcohol) 18 carbon atoms
 Hydrolysis = sphingosine alcohol + FA
+ phophoric acid + choline base

33. GLYCOLIPIDS
(GLYCOSPHINGOLIPIDS)
 Glycolipids are widely distributed in every tissue
of the body, particularly in nervous tissue such as
brain. They occur particularly in the outer leaflet
of the plasma membrane, where they contribute to
cell surface carbohydrates.
 Glycolipids are cpd. Lipids with carbohydrate
radical as prosthetic group.
 Contain Sphingosine alcohol + FA
+ carb. group.

34. GLYCOLIPIDS contain:
 Cerebrosides:
Found mainly in brain
Contain FAs with 24 C atoms
Four types:
 Nervon:
Shpingosine alc. + galactose
+ nervonic acid
 Oxynervon:
Shpingosine alc. + galactose
+ oxynervonic acid

35. Cerebrosides:
Four types: cont.,
 Cerebron
Shpingosine alc. + galactose
+ cerbronic acid
 Kerasin:
Shpingosine alc. + galactose
+ lignoceric acid

36. Sulfolipids (Sulfatides)
 Are glycolipids present in liver, muscles and
testis.
 Similar to cerebrosides in structure, but they
have more sulfuric acid.

37. Gangliosides
 Present in nerve ganglia.
 Contain:
 carbohydrate radical
 FA usually Stearic or Oleic acid

38. Proteolipids
 Present in nervous tissue.
 Contain lipids + Protein
 Lipid surrounds the protein
 Insoluble in water
 Soulble in fat solvents.

39. Derived Lipids
 Produced by hydrolysis of simple or conjugated
lipids.
 Associated with lipids in nature.
 They include:
Fatty acids Alcohols Squalene
Steroids Fat soluble vitamins

40. Alcohols
 The most important are:
Glycerol in TAG and phosphoglycerides.
Sphingosine (sphingol) in sphingolipids.
Long chain monohydroxy alcohols in waxes,
e.g. mericyl alcohol.
Sterols.
Vitamin A and D.

41. Squalene
 It is polyunsaturated hydrocarbon containing 30
carbons, formed during synthesis of different
steroids in the body.
Activated acetic acid → Squalene →
→ Cholesterol → other steroids
Fat soluble vitamins
 Vitamin A, D, E and K.
 Vitamin A and D are alcohols

42. Steroids
 They contain C17 steroid nucleus or
Cyclo-Pentano-Perhydrophenanthrene ring
(CPPP)

43. Classification of Steroids
Steroids
Sterols
Steroid
Hormones
Bile acids
(C24)

44. Steroid
Hormones
Sex hormones
Corticoids
(C21)
Male (C19) Female Glucocorticoids Mineralocorticoids
Estrogen (C18)
Progesterone (C21)

45. Sterols
 Sterols Have Four Fused Carbon Rings
 Sterols means SOLID (ster) alcohols
 Classified into:
 Zoo sterols: present in animals
(Cholesterol)
 Phytosterols: present in higher plants
(not physiologically important)
 Mycosterols: present in lower plants (yeast & fungi)
(Ergosterol, precursor of Vitamin D2)

46. Cholesterol

47. Importance of Cholesterol
 Formed from activated acetic acid (active
acetate).
 It is the precursor of all steroids in animal
body.
 Widely distributed in all tissues.
 Higher conc. present in nervous tissues,
liver, adrenals, gonads, skin and adipose
tissues.

48. Importance of Cholesterol (cont.,)
 Plasma conc. (100-200mg/dL)
(30% as free cholesterol and 70% as cholesteryl
esters).
 Hypercholesterolemia → atherosclerosis
 Excretion: About 1 g of cholesterol is eliminated from the body per day.
 Bile in the form of bile salts: Cholesterol,
cholesteryl esters and dihydrocholesterol.
 Large intestine: is reduced by bacteria to give
coprostanol.

49. Importance of Cholesterol (cont.,)
 Cholesterol converted in the liver to
7-Dehydrocholesterol which converted to
vitamin D3 under skin by the action of UV
rays.

50. Bile acids
 Hydroxy derivatives of C24
steroid (Cholic acid).
 Bile acids are polar
derivatives of cholesterol
that act as detergents in the
intestine, emulsifying
dietary fats to make them
more readily accessible to
digestive lipases.
 Aid in lipid digestion.
Cholic acid

51. Types of Bile Acids
Bile Acids
Primary Bile acids
(Synthesized in the liver)
Secondary Bile acids
(formed in the large
intestine by Bacteria)
Cholic acid
Chenodeoxy cholic
acid
Deoxycholic acid Lithocholic acid

52. Bile Salts
 Synthesized by conjugation of bile acids
with Glycine (80%) or Taurine (20%).
 Excreted by liver in bile as sodium salts,
Sodium-glycocholate
Sodium-taurocholate
 Pass to the intestine, reabsorbed and return
to the liver to be excreted again in bile
(enterohepatic circulation of bile salts)

53. Importance of Bile Salts
 Conversion to bile salts is an important
mechanism for cholesterol removal from
blood.
 Emulsification of fat in the intestine is
essential for their digestion and absorption.
 Prevent precipitation of cholesterol in bile
and prevent formation of cholesterol stones.
 They stimulate liver cells to secrete more
bile (choleretic effect).