2. Definition, function, distribution & classification
Simple lipids definition, source, structure, fatty acid classification &
properties
Complex lipids structure, classification & function
Derived lipids structure, function & related diseases
Lipids digestion & absorption
Objectives
3. Definition
• Lipids are heterogeneous group of compounds that are
characterized by their insolubility in water.
• The hydrophobic nature is due to predominance of non-
polar hydrocarbon chains.
4. Function of Lipids
1. Lipids are the richest source of energy (9kcal/g).
2. Most of the energy stored in the body is in the form of lipids
(triglycerides).
3. lipids provide the body with the essential fatty acids.
4. Lipids provide the body with a group of vitamins called “The fat
soluble vitamins, A, D, E, and K”.
5. Function of Lipids (continue)
5. Lipids share in cell membrane structural components.
6. Lipids enter in structure of steroid hormones are critical chemical
messengers that allow tissues of the body to communicate with one
another.
7. Protection. Fats serve as a shock absorber, or protective layer, for
the vital organs.
8. Insulation. Fat stored beneath the skin (subcutaneous fat) serves to
insulate the body from extremes of cold temperatures.
7. A-Tissue fat
It is constant.
Not affected by starvation.
Never oxidized to give energy.
It is present in every cell and in cell membrane.
It is composed from: cholesterol, phospholipids,
glycolipids, and small amount of triglycerides.
8. B) Depot fat
Fats which are stored in the body in the adipose tissues.
The distribution of depot fats is as follows:
1- Under the skin.
2- Around the important organs such as kidney
Composition of depot fat:
Adipose tissue is composed of triglycerides (90%) & small amount of cholesterol
and phospholipids.
Function of depot fat:
1) An important source of energy
2) Supports & protects some important internal organs e.g. kidney.
3) Depot fat provides the body with vitamin D3 by exposure of skin to U.V light
of sun.
4) Depot fat act as heat insulator.
9. 9
Classification of lipids
• Simple lipids (Neutral lipids):
• Ester of fatty acid with alcohol e.g. triglycerides.
• Triglycerides (Triacylglycerol) are also called fat or oils
• Fats: lipids that are solid at room temperature
• Oils: lipids that are liquid at room temperature
• 95 % lipids in foods, are fats and oils & 90% of the lipids stored in the body, are
triglycerides.
• Complex lipids:
• They are esters of fatty acids with alcohols. In addition it contains additional groups e.g.
phospholipids , glycolipids & lipoproteins.
• Derived lipids:
• They are formed from simple and compound lipids by hydrolysis.
• They are fatty acids, steroids, and fat-soluble vitamins (A, D, E, and K).
11. I-Simple lipids
Neutral lipids (Triglycerides)
Definition:
These are esters of fatty acids with the tri-hydroxy alcohol, glycerol.
They are called neutral because they are uncharged.
They include two type:
• Solid at ordinary temperature and are called fats.
• Liquid at ordinary temperature and are called oils.
12. Sources of neutral lipids
In plants:
Cotton seed oil, olive oil, Coconut oil, lin seed oil, sesame oil
and Soya bean oil. All of these oils are called edible oils.
In animals:
Butter and animal fats.
Marin oils (Oils of sea animals):
Cod liver oil and shark liver oil.
These oils are very rich in vitamin A and vitamin D.
13. Chemical constituents of triglycerides
• They are esters resulting from the reaction of three
fatty acids (R-COOH) and glycerol (trihydroxy alcohol).
CH2OH
CHOH
CH2OH
R COOH
R COOH
R COOH
CH2
CH
CH2
O C R
O
O C R
O
O C R
O
+ -3H2O
Glycerol 3 molecules
of fatty acids
general formula
of triglycerides
14. 1-Glycerol:
It is a trihydroxy alcohol (i.e., containing three OH groups).
It is contains two terminal primary alcoholic groups and one
secondary alcoholic group in the middle.
Hydrophilic and charged.
15. 15
2- Fatty acids
• Fatty acids are hydrocarbon chain with carboxylic group (carboxylic acids).
Fatty acids are classified according to several bases
as follows:
According to Saturation (presence or absence of double bonds)
According to Nutritional Value
16. 16
Fatty acids Classifications
According to Saturation (presence or absence of double bonds)
they are classified into:
A-Saturated Fatty Acids
They contain no double bonds.
They are solid at room temperature except if they are short chained
(2-4 carbon).
• Plamitic acid: (16C) [CH3−(CH2)14−COOH]
• Stearic acid: (18C) [CH3−(CH2)16−COOH]
• Arachidic acid: (20C) [CH3−(CH2)18−COOH]
17. B-Unsaturated Fatty Acids
They contain double bond & classified into 2 groups:
i- Monounsaturated fatty acids:
They contain one double bonds
Palmitoleic, (16C) C16:1∆9
CH3−(CH2)5-CH=CH-(CH2)7COOH
Oleic acid, (18C) C18:1∆9
18. ii-Polyunsaturated fatty acids (PUFA):
They contain more the one double bond
The most important are :
Linoleic acid: (18C) C18:29, 12 contains two double bonds between
C9−10 and C12−13
CH3−(CH2)4−CH=CH−CH2−CH=CH−(CH2)7−COOH
Linolenic acid: (18C) C18:39, 12, 15 contains three double bonds
between :
C9−10&C12−13&C15−16
Arachidonic acid: (20C) C20:45, 8, 11, 14.
contain 4 double between C5−6&C8−9 &C11−12 &C14−15
21. 21
Double bonds in fatty acids are in the cis-configuration
Trans –double bonds are unnatural and found in processed foods (margarine) where partial hydrogenation of
vegetable oils is used in their preparation.
22. According to Nutritional Value:
1) Non essential Fatty acids:
Synthesized in Body and include all Saturated and Mono-
unsaturated.
2) The essential fatty acids:
These are polyunsaturated fatty acids (PUFA) which contain more
than one double bond.
Their essentiality is due to inability of the human body to
synthesize them, accordingly they must be taken in the diet
23. • Types of essential fatty acids:
• Omega 6 fatty acid: Linoleic acid & arachidonic acid which is found in most
vegetable oils.
• Omega 3 fatty acids: Linolenic acid which is found in fish oil (decrease risk of
cardiovascular disease).
• Functions of essential fatty acids:
• Immune function
• Component of cell membrane
• Produce hormone like substance (prostaglandins)
• Increase solubility of cholesterol.
24. Properties of neutral lipids
1- They are insoluble in water (hydrophobic) but soluble in fat solvents
(ether, benzene ……..).
2- Neutral lipids may be oils or fats. Oils are liquid at ordinary
temperature. Fats are solid at ordinary temperature.
3- They are hydrolyzed (digested ) by pancreatic lipase enzyme into
glycerol and free fatty acids.
CH2 O
C H
O
CH2
C
C
O C
R1
R3
R2
O
O
O
3 H2O
H2C OH
C H
HO
H2C OH
OH
C
R1
O
OH
C
R3
O
+ OH
C
R2
O
Lipase or Acid
Triacylglycerol Glycerol Free fatty acids
25. 4- Hydrogenation of oils & hardening of oils:
Vegetable oils when hydrogenated by addition of hydrogen to
the unsaturated fatty acids of oils they produce the
corresponding artificial fats (margarine ).
It is advisable not to saturate all double bonds in the
unsaturated fatty acids, otherwise the margarine will be very
hard & less biologically importance.
Oils Artificial fat
hydrogenation
26. 26
II- Complex lipids
• They are esters of fatty acids with alcohols. In addition it contains additional groups
Classification of complex lipids:
• According to the additional group, complex lipids are divided into
Phospholipids (contain phosphate)
Glycolipids (contain CHO)
Lipoproteins (contain Proteins)
• According to the nature of the alcohol found, complex lipids are subdivided into
Glycerolipids or, the alcohol is glycerol.
Sphingolipids, the alcohol is sphingosine.
28. 28
A- Phospholipids
1. Glycerophospholipids
• Phospholipids is a member of compound lipids
• Phospholipid: alcohol(glycerol) + 2 fatty acids + a phosphate group + additional group
• Functions of phospholipids
Component of cell membrane (amphipathic lipid)
Emulsifier (help to mix fats with water) During digestion & transport of lipids and
also it emulsify cholesterol in bile
The best-known phospholipid is lecithin (contains choline base) present in lung
surfactant prevents collapse of lung alveoli.
29. • Sphingomyelins, contain phosphate (it is a phospholipids)
• Sphingomyelins consist of alcohol (sphingosine) + one fatty acid +phosphate
+ choline
• Functions of sphingomyelins:.
• They are present in most of animal membranes especially the myelin sheath of nerve cells.
A- Phospholipids
2. Shingophospholipids
30. 30
B- Glycolipids
• They are consist of alcohol (sphingosine)+ one fatty acid+ simple or complex CHO.
• If the CHO is simple, they are called cerebrosides
• If the CHO is complex, they are called gangliosides
• Function of cerebrosides:
• Cerebrosides occur in large amounts in white matter of brain and in myelin sheath of
nerves.
• Functions of gangliosides:
• They are abundant in grey matter of brain.
• They are components of hormone receptors.
• They are also involved in cell-cell recognition, growth, differentiation.
31. Lipoproteins are conjugated lipids in which the lipid part (e.g.
cholesterol, phospholipids or triglycerides) combines with protein
part.
Importance of plasma lipoproteins (Function):
They are conjugated with proteins to form
lipoproteins which are converted in to
water soluble substances and can be
transported in the plasma.
C- Lipoproteins
32. Types of Lipoproteins:
Chylomicron
Very low density lipoproteins
(VLDL).
Low density lipoproteins (LDL).
High density lipoproteins (HDL).
33. The main differences between -and -
lipoproteins of blood:
-Lipoproteins -lipoproteins
- High density, HDL - Low density, LDL
- Carries ⅓ of total blood
cholesterol
- Carries ⅔ of total blood
cholesterol .
- High phospholipid content - Low phospholipid content
- -globulin is present - -globulin is present
- Protects against
atherosclerosis
- Their blood level is increased in
atherosclerosis.
34. III-DERIVED LIPIDS
• These are substances derived from the simple and
conjugated lipids by hydrolysis.
Simple lipids Derived lipids
Conjugated lipids
Derived lipids include:
Fatty acids
Glycerol.
Sphingosine.
sterols and steroids.
Lipid soluble vitamins ( A,D,K,E).
35. 35
Sterols
• A sterol contains a four ring carbon structure with any of a variety of side
chains attached.
• The most famous sterol is cholesterol
• Food sources of sterols
• Plants and animals foods contain sterols, but only those from animal contain
cholesterol.
• plant sterols are structurally similar to cholesterol, these plant sterols
interfere with cholesterol absorption thus lowering blood cholesterol levels.
36. 36
Cholesterol
• Produced by the liver, we make all we need (non-essential). Found only in animal
product.
• Functions
1. Component of cell membrane.
2. Precursor for steroid hormones
Estrogen, testosterone.
3. Precursor for bile acids.
4. Precursor for Vitamin D3.
37. Properties of cholesterol :
1. Cholesterol forms characteristic crystals having
a specific notch at one angle.
1. It is an alcohol i.e. contains one secondary alcoholic group at
carbon-3.
2. It is insoluble in water but soluble in fat solvents (Ether,
chloroform ………. etc).
4. Found only in animal product.
38. The level of the blood cholesterol is normally (140 – 200 mg/dl).
Increase cholesterol level is associated with high risk of developing
atherosclerosis & gall bladder stones.
LDL particles carry 2/3 of blood cholesterol. On the surface of cells,
there are receptors for LDL, when LDL binds to these receptors it is
endocytosed inside cell
Clinical consideration & related diseases
39. So LDL accumulate in the blood and cholesterol of LDL forms plaques
inside the blood vessel which makes it stiff and narrows its lumen
(atherosclerosis). If this occurs in coronary arteries which supply the
heart, leads to Oxygen shortage and Anginal pain.
The presence of high level of HDL prevents from this because it transfer
cholesterol from blood to liver where its excreted outside body. HDL
protects against atherosclerosis.
Clinical consideration & related diseases
40.
41. Lipid digestion
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41
• Dietary lipids are:
A. Triacylglycerol,
B. Cholesterol and cholesterol ester
C. Phospholipids
D. Fat-soluble vitamins (A,D, K, E)
• Lipid digestion required bile salts which are made by the liver.
• Bile salts emulsify lipid droplets, thereby enhancing their
digestion.
43. A) Triacylglycerols (TAG).
• The digestion of TAG begins in the stomach by gastric lipase then
pancreatic lipase from pancreas in small intestine (most important).
Triglycerides are digested into monoacylglycerol and 2 fatty acids.
B) Phospholipids (PL)
• PL are digested by phospholipase to form lysophospholipids and fatty acids.
C) Cholesterol ester (CE) and cholesterol (C)
• CE is converted to free cholesterol by the action of cholesterol esterase.
• Cholesterol is not digested.
D) Fat-soluble vitamins are not digested.
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44. Absorption and transport of lipids
All of the products of digestion are absorbed into
enterocytes.
Inside the enterocytes the fatty acid combined with the
mono-acylglycerols, lysophospholipids and cholesterol
reforming TAG, phospholipids and cholesterol esters.
These molecules are water insoluble so they can not be
transport to the blood in this form. Instead these
molecules associate with protein (apoB-48) forming a
very large lipoprotein called chylomicrons which is
transported to the lymph and then enter the blood.
Vitamins A, D, E & K are also transported by
chylomicrons to blood via lymph.
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45. Reference
- Denise R. Ferrier. (2013) Biochemistry Lippincott illustrated
review, 7th edition.
- Morris Hein, Scott Pattison, Susan Arena. (2015) Introduction to
general, organic and biochemistry, 7th edition.
- Nelson, D. and Cox, M. (2016) Lehninger principles of
biochemistry, 7th edition.
