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Def: lipids are heterogeneous group related
to fatty acids.
Lipids are relatively insoluble in water.
They are soluble in nonpolar solvents such as
chloroform , diethyl ether, acetone, benzene
and ether.
The hydrophobic (water hating) nature of
lipids is due to the predominance of
hydrocarbon chain.(-CH2-CH2-CH2-) in their
structure
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Lipids are important dietary constituent
because:
A) They are a source of high energy value.
B) They contain fat soluble vitamins.
C) They contain essential fatty acids.
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Lipids in adipose tissues serve as storage
form of energy.
They serve as thermal insulator in the
subcutaneous tissues.
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Lipoproteins(a combination of fat and
proteins) are important because:
1. They enter in the structure of cell
membrane and mitochondria.
2. They serve as a transport form of lipids in
the blood .
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Simple
Complex
Derived
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Simple lipids are esters of fatty acids with
various alcohols.
(Ester bond = R-coo-R).They are either fat or
waxes.
R-COOH(H) + R-(OH)=> R-COOH-R + H2O
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Are esters of fatty acids with glycerol .Fat are
either solid or liquid.
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Are esters of fatty acids with higher molecular
weight alcohols containing one (-OH) group
i.e monohydric alcohols.
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Are esters of fatty acids and alcohols ,in
addition of other groups . They include:
Phospholipids: they consist of
Fatty acids + alcohols + phosphoric acids
residue + nitrogenous base. They include:
Glycerophospholipids : when alcohol is
glycerol.
Sphignophospholipids : where the alcohol is
sphingosine.
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Glycolipids : they consist of fatty acids +
sphingosine + carbohydrate.
Other complex lipids are :which include
sulpholipids (containg suphur) ,amino
lipids(containing amino acids) and
lipoproteins (containing proteins).
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Substance which are given by hydrolysis of
simple and complex lipids.
Substance which are insoluble in water but
soluble in nonpolar solvents as :
Fatty acids.
Glycerol
Steroids
Alcohols
Ketone bodies
Fatty aldehydes
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Neutral lipids: are those which carry no
charge and include:
Neutral fats: (acylglycerols).
Cholesterol and cholesteryl esters.
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Water insoluble
They are monocarboxylic acid containing
They are mostly aliphatic (not branched)
Fatty acids are present as free fatty acids in
plasma.
Fatty acids occur in natural fats contain an even
number of carbon atoms , because they are
synthesized from 2 carbon units.
Fatty acids may be saturated (containing no
double bonds) or unsaturated (containing one or
more double bonds).
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Solubility:
Short chain fatty acids e.g acetic (2C) and butyric
(4C) are soluble in water.
Long chain fatty acids are insoluble in water in
nonpolar solvents.
Melting points: this depend upon length on fatty
acids and the degree of unsaturation , so
1.short chain and unsaturated fatty acids are
liquid at RT.
2.long chain and saturated fatty acids are solid at
RT
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Have no double bonds in the chain’.
General formula is -CH3-(CH2)n-CooH
,where (n) equals the number of methylene (CH2) group between the methyl and
carboxylic group.
The systemic name of saturated fatty acids
ends by the suffix (-anoic).e.g palmitic
acids(16 C) has symmetric name hexadeconic
acids(hexa =6;deca10)
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Have one (monosaturated) or more
(polyunsaturated) double bonds in the chain.
The general formulae is Cn-H2n-1-COOH.
The systemic name is unsaturated fatty acids
ends by the suffix (-enoic) e.g oleic
acids(18C) has systemic name octadecenoic
acids (octa=8,deca=10)
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They are called non-essential fatty acids
because they are synthesized in the body
.Thus need not be obtained from the diet.
They can be synthesized from acetyl CoA
(Activate acetate) derived from glucose
oxidation.
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They are called essential because they cannot
be synthesized in the body . They must be
supplied diet
Essential fatty acids include those which
contain more than one double bonds
(polysaturated fatty acids) e.g linolenic acids
and arachidonic acids.This is because there
are no human enzyme that can be introduced
a double bond except at the ninth carbon
atoms(9-10) position.
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Normal growth
They enter in the structure of phospholipids
and cholesterol esters
Vegetable oil e.g corn oil is rich in essential
fatty acids
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They are formed only from alcohols and fatty
acids.
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They are called neutral fats because they
carry no charge.
The main site for storage of fat in human is
the cytoplasm of cells located in
subcutaneous fat and around important
organs . Adipose tissues is important source
of energy .Each gram fat gives 9.3Kcal.
Human fat is liquid at RT and contain high
content of oleic acid.
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In animals
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In plants
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Marine oil
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Butter and lards
Cotton seed oil ,
linseed oil, sesame
oil and olive oil.
Cod liver and shark
oil.
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These include phospholipids , glycolipids ,
lipoproteins , sulpholipids , and aminolipids .
Phospholipids :They contain phosphoric acids
residues .They are classified into
glycerophospholipids (contain glycerol) and
sphingophospholipids(contain sphingosine).
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Structure :
1. Glycerol
2. Saturated fatty acid(attached to 1(α)
position.
3.Unsaturated fatty acids (attached to2(β)
position.
4. Choline base (attached to phosphoric acid.)
.Base differs in various phopholipids.
lecithin
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It enters in the structure of cell membrane .It
is most abundant phopsholipid in cell
membrane.
It act as body store of choline.
Importance of Choline :
1. It is important in nerve transmitter.
2. It acts as methyl donor in transmethylation
reaction.
3.Dipalmitoyl lecithine(i.e lecithine which
contain 2 palmitic acid residue)acts as
surfactant in the lung.
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Dipalmitoyl lecithine continuosly secreted by the
lungs cells in the alveolar wall,forming a monolayer
over the watery surface of the alveolus and so lower
the surface tension .This help expiration and
inspiration.
During expiration ,the surfactant becomes solid
under pressure . This prevents the adherence of
alveolar wall.
During inspiration ,the surfactant makes the lungs
easier to expand.
In premature babies :lungs do not secret enough
surfactant .This leads to lungs collapse and death
from respiratory failure . Treatment of this case need
the putting babies in incubator and administration of
surfactant locally in the lungs.
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It is one of activating factor of coagulation
mechanism
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They are called complex glycolipids , because
they contain in addition to hexose , one or
more sialic acid molecules.
Function:
They acts as receptors at cell membrane
They are present in high concentration in
brain.
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Cholesterol(animal origin)
Ergosterol (plant origin)
Vitamin D group
Bile salt
Steroids hormones
1.Male sex hormones
2. Female sex hormones
3.Adrenal cortical hormones
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Distribution in the body:
It is present in all cells especially;
Adrenal cortex.
Liver and kidney
Brain and nerve tissues
The level of blood cholesterol is normally less
than 220mg/dl . Any increase above this level
is called as hypercholesterolemia.
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Structure: similar to cholesterol but differ in
1.double bonds
2. the side chain is unsaturated and has extra
methyl group.
Properties;
It is plant sterol, poorly absorbed by small
intestine.
Function: It gives vitamin D2 by ultra violet
rays.
Ergosterol
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Bile salt are bile acids
Function:Bile salts are important for digestion
and absorption of lipids.
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Estrogens: 3 types ;estrone , estradiol and
estriol.
Site for production:
1.Ovary and placenta in female
2.Adrenal cortex in both male and female.
Functions
1.They stimulate the development of female
sex characters and organs.
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Structure:
Ketone group at C3
Double bond between C4 and C5.
Methyl group at C10 and C13
Methylketone at C17
Site of production:
Ovary and placenta in female.
Adrenal cortex in both male and female
Function:
It prepares the uterus for implantation of the
ovum.
It stabilizes pregenancy (prevent abortion)
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Testerone :
Structure
Ketone group at C3
Double bond between C3 and C5.
2 methly group at C10 and C13
-OH at C17.
Site of production:
Intestinal cells of leyding of the testis in male
Adrenal cortex in both male and female.
Function: It stimulates the development of male
sex characters and organs.
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Site of production:
Adrenal cortex
Function:
Glucorticoids :control the metabolism of
carbyhydrates , proteins, and fats.
Minerlcorticoids: control the metabolism of
Na ,KCl, and water.