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

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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

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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