Lipid ChemistryPresented By
Ayman Elsamanoudy
Salwa Abo El-khair
6
1. By the end of this chapter the student should be able to:
define lipids.
describe the biological importance of lipids.
point out basic lipid chemistry.
classify lipids.
explain the chemistry and main function of simple, compound
and derived lipids.
2. By the end of this chapter the student should be able to
apply biochemical knowledge on analyzing biochemical bases of
the diseases through case study.
3
Objectives:
III Derived lipids
They are compounds derived from simple and
compound lipids by hydrolysis .
e.g. fatty acids and glycerol.
Also; they include substances related to lipids as:
Steroids,
Isoprenoids,
Eicosanoids
Fat soluble vitamins.
Steroids They are a large group of biologically
important compounds.
All of them contain a steroid nucleus, which
is
Cyclo-Pentano –Perhydro-Phenanthrene
nucleus
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Cyclopentano -perhydrophenanthrene
(steroid) nucleus
Steroids Steroid compounds include:
1. Sterols (steroid alcohols).
2. Steroid hormones.
3. Vitamin D.
4. Bile acids and salts.
5. Caradiac glycosides.
6. Toad poisons.
Steroids1- Sterols
They are complex alcohols that contain
hydroxyl group (do not contain carbonyl
or carboxyl groups)
e.g. cholesterol and ergosterol.
Cholesterol is present in animal tissues.
Ergosterol in plant tissues.
A- Cholesterol (Animal
sterol)
It is the best-known sterol.
It is the most abundant animal
sterol.
27 C atoms molecule .
It is formed of:
(steroid) nucleus.
(-OH) at C3.
Double bond between C5 and C6.
2 CH3 groups at C10 &C13
Side chain of 8 carbon atoms at C17.
Cholesterol It is formed of:
steroid nucleus.
2 CH3 groups at C10 &C13
Alcoholic hydroxyl group (-OH) at C3.
Double bond between C5 and C6.
Side chain of 8 carbon atoms at C17.
SteroidsProperties of cholesterol
1. Cholesterol is insoluble in water but soluble in fat
solvents.
2. It is present in every animal cell but mainly in adrenal
cortex, liver, kidney, brain and nervous tissues.
3. It is present in human blood in concentration of 150-270
mg/dl.
4. Reduction by intestinal bacteria converts cholesterol into
dihydrocholesterol (coprastanol) by saturation of the
double bond between C5 and C6. coprastanol is present
in faces.
Functions of cholesterol
Cholesterol share in the structure of cell membrane.
Cholesterol is the precursor of all steroid hormones.
It is oxidized in the liver to give bile acids and bile salts.
It is the precursor of vitamin D3 .
Functions of cholesterol
It is oxidized to 7 dehydro-cholesterol by introduction
of double bond between C7 and C8.
7 dehydro-cholesterol is pro-vitamin D3 because it is
converted to vitamin D3 when the skin is exposed to
ultraviolet rays.
Colour reactions of cholesterol
Lieberman Burchard test:
Cholesterol bluish green colour.
Salkowski test:
cholesterol bluish red to purple
.
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Conc.H2SO4+acetic acid
Conc.H2SO4+chloroform
B- Ergosterol
It is plant sterol.
Structure (28 carbon):
Steroid nucleus.
(-OH) at C3.
2 double bond :
-between C5 and C6 &
-between C7 and C8.
2 CH3 groups at C10 &C13
Side chain of 9 carbon atoms at
C17. It contains double bond
between C22 and C23 and an
extra methyl group at C24.
Function of ergosterol
- Ergosterol is provitamin D2 because it is
converted to vitamin D2 when the skin is exposed
to ultraviolet rays.
Sterols
Cholesterol Ergosterol
Source Animal source Plant source
Number of carbon atoms
27 C 28 C
Side chain 8 carbon atoms 9 carbon atoms
Angular methyl group in the side chain at C24
Absent Present
Double bond between C7 and C8
Absent Present
SterolsCholesterol Ergosterol
Double bond in the side chain between C22 and C23
Absent Present
Absorption from small intestine
Easily absorbed Poorly absorbed
Functions •Precursor of all steroid compounds e.g. steroid hormones and bile acids.•It gives 7 dehydrocholesterolwhich is provitamin D3
•It is provitaminD2
Steroids
2- Steroid Hormones
These are hormones that contain:
steroid nucleus.
They include:
A. Sex hormones:
1) Male sex hormone (testesterone).
2) Female sex hormones (estrogens and
progesterone).
B. Adrenal cortex hormones.
C. Active forms of vitamin D.
Steroid hormonesProgesteroneEstrogensTestesterone
21 carbon
• Steroid nucleus
• Oxygen at C3
• = between C4 and C5
• 2 CH3 at C10 and C13
• Methyl keto at C17
18 carbon
[estradiol (most active) , estroneand estriol]
• Steroid nucleus
• OH at C3.
• A ring is aromatic
•1 CH3 at C13
• OH at C17
19 carbon
• Steroid nucleus
• Oxygen at C3
• =between C4 and
C5.
• 2 CH3 at C10
and C13
• OH at C17
Structure
Progesterone
CH3
C=O
ProgesteroneEstrogensTestesterone Ovary and placenta
Adrenal cortex(males and females).
Ovary and placenta
Adrenal cortex(males and females).
Interstitial cells of Leyding (testis).
Adrenal cortex(males and females).
Site of secretion
1) prepares the uterus for implantation of the ovum
2) stabilizes pregnancy
3) development of breast alveolar system
4) secretory phaseof the menstrual cycle
5) anabolic effect
1) development of female sex organs
2) female secondary sex characters
3) development of breast duct system
4) proliferative phase of the menstrual cycle
5) anabolic effect
1) development of male sex organs
2) male secondary sex characters.
3) important for spermatogenesis
4) anabolic effect
Function
B- Adrenal cortex hormones
They are secreted from the adrenal cortex.
They are classified into:
glucocorticoids & mineralocorticoids
mineralocorticoidsglucocorticoids
Aldosterone (OH at C11)
11-deoxy corticosterone
11-deoxy cortisol
corticosterone
cortisol
(OH at C11)
Examples
21 carbon• Steroid nucleus.
• Oxygen at C3
• = between C4 and C5.
• 2 CH3 at C10 and C13
OR
CH3 at C10 + Aldehyde group
at C13.
• Ketol group at C17.
• OH at C11 (may be absent)
21 carbon
• Steroid nucleus
• Oxygen at C3
• = between C4 and C5
• 2 CH3 at C10 and C13
• Ketol group at C17
• OH at C11
Structure
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11 deoxycortisol11 deoxy
corticosterone
OH
OH
Adrenal cortical hormoneAldosteroneMineralocorticoid
sGlucocorticoids
21 carbon
Aldosterone
Aldehyde group at C13
Ketol group at C17.
21 carbon
(11 deoxy cortisol)
No Oxygen at C11
Ketol group at C17.
21 carbon
Cortisol
(17 hydroxy
corticosterone)
Ketol group at C17.
Structure
OH
mineralocorticoidsglucocorticoids
Adrenal cortex.Adrenal cortex.Site of secretion
1) sodium, chloride and water retention (↑absorption).
2) potassium excretion (in the urine).
Aldosterone is the most powerful mineralocorticoid
1) hyperglycemic hormones; they increase blood glucose.
2) stimulate hepatic lipogenesis from carbohydrate
3) suppress immune response
4) suppress inflammatory and allergic responses.
5) Catabolic hormones
Functions
Lipid ChemistryPresented By
Ayman Elsamanoudy
Salwa Abo El-khair
7
SteroidsC- Active forms of vitamin D
1, 25 dihydroxy vitamin D3 (calcitriol) &
1, 25 dihydroxy vitamin D2 are the active forms of vitamin D.
They are considered hormones :
Because : they are
-synthesized in an organ
(skin),
-activated in other organs
(liver and kidney)
- exert function on other organs
(small intestine and bones).
3- Steroid vitamins ( D2, D3 )
Vitamin D
Functions
They are fat-soluble vitamins that have a role
in calcium metabolism.
They increase calcium absorption from gastro
intestinal tract and increase bone ossification.
4- Bile acids (24 Carbons):
They are formed from cholesterol in the liver by oxidation of the
side chain.
There are 4 bile acids:
A- Cholic acid (1ry bile acid in the liver)
It is the main bile acid in humans.
It is 3, 7, 12 –trihydroxy cholanic acid.
B- Chenodesoxycholic acid (1ry in the liver)
It is 3, 7 dihydroxy cholanic acid.
C- Deoxycholic acid (2ry in the intestine)
It is 3, 12 dihydroxy cholanic acid.
D- Lithocholic acid (2ry in the intestine)
It is 3 hydroxy cholanic acid.
1ry bile acids -OH at C7
2ry bile acids
Formation of bile salts
Bile acids unite with glycine to form glycocholic acid.
Glycocholic acid unites with sodium or potassium to form sodium glycocholate or potassium glycocholate.
Or they may unit with taurine (derived from amino acid cysteine) to form taurocholic acid.
Also, taurocholic acid unites with sodium or potassium to form sodium taurocholate and potassium taurocholate.
So, bile salts are:
Sodium glycocholate, Potassium glycocholate,
Sodium taurocholate & Potassium taurocholate .
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Cholicacid
+ glycine GlycocholateNa OR K
glycocholate
+taurine TaurochlateNa OR K
taurocholate
Function of bile salts:
Bile salts have a role in lipid digestion and absorption:
1.They activate the pancreatic lipase enzyme
responsible for digestion of triglycerides.
2.Emulsification of lipid particles converting them
into small particles
3.They help absorption of the water insoluble fats
by forming more soluble hydrophilic micelles.
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Isoprenoids
They are unsaturated hydrocarbons.
They are formed of repeated units of 5 carbon
atoms called isoprene units.
They include:
1. Ubiquuinone, which is a member of the respiratory
chain in mitochondria.
2. Dolichol, which is a long chain unsaturated alcohol
which chares in glycoprotein synthesis.
3. Carotenes, which are provitamin A.
4. Rubber.
5. Camphor.
6. Vitamin K,E
Carotenes
Criteria of carotenes:
They are unsaturated hydrocarbons
They are formed of 40 carbon atoms
They have the general formula C40H56.
They are formed of repeated units of 5 carbon
atoms called isoprene units.
They are orange in colour.
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Sources of carotenes:
plant sources as carrots and plant leaves.
Importance of carotenes
They are precursors of vitamin A.
Types of carotenes
There are 3 types of carotenes α, β and γ according to
the types of the 2 ionone rings present:
α carotene, which contains one β and one α ionone
rings.
β carotene, which contains 2β ionone rings.
γ carotene, which contains one β and one γ ionone rings.
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Carotenes
Structure
They are formed of 2 ionone rings connected by a
chain of repeated isoprene units.
Carotenes
α carotene contains one β ionone ring and one α
ionone ring.
It gives one molecule of vitamin A.
Isoprenoids
β carotene contains 2β ionone rings.
It gives 2 molecules of vitamin A.
Isoprenoids
γ carotene contains one β ionone ring and one
γ ionone ring.
It gives one molecule of vitamin A.
Activity 1- Compare between each of the followings :
1- choesterol & ergosterol
2- testosterone & estrogens
3- estrogens & progesterone
4- glucocorticoids & mineralocorticoids
2- Enumerate the types of bile acids &mention its
biological importance
3- Bile salts(discuss)
4- Why is vitamin D considered to be a hormone 45
Choose the best correct answer
1- The most potent mineralocorticoid is:
a) cortisol
b) deoxycortisol
c) deoxycorticosterone
d) aldosterone
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-One of the following steroids contains phenolic
group:
a) Testosterone.
b) Cortisol .
c) Estradiol.
d) Progeterone
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11/17/2014 48Ahmed A.Albadry
GREAT
THANKS
Ayman Elsamanoudy
Salwa Abo El-khair