Lipid Chemistry Presented 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. Objectives: 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
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
Cyclopentano -perhydrophenanthrene (steroid) nucleus 6
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.
1- Sterols Steroids 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.
Steroids Properties 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 doublebondbetween 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 Conc.H2SO4+acetic acid bluish green colour. Salkowski test: cholesterol. 14 Conc.H2SO4+chloroform bluish red to purple
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 Double bond between C7 and C8 Absent Absent Present Present
Double bond in the side chain between C22 and C23 Absorption from small intestine Functions Sterols Cholesterol Absent Easily absorbed Precursor of all steroid compounds e.g. steroid hormones and bile acids. It gives 7 dehydrocholesterol which is provitamin D3 Ergosterol Present Poorly absorbed It is provitamin D2
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.
Structure Steroid hormones Testesterone 19 carbon Steroid nucleus Oxygen at C3 =between C4 and C5. 2 CH3 at C10 and C13 OH at C17 Estrogens 18 carbon [estradiol (most active), estrone and estriol] Steroid nucleus OH at C3. A ring is aromatic 1 CH3 at C13 OH at C17 Progesterone 21 carbon Steroid nucleus Oxygen at C3 = between C4 and C5 2 CH3 at C10 and C13 Methyl keto at C17 CH3 C=O Progesterone
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Testesterone Estrogens Progesterone Site of secretion Interstitial cells of Leyding (testis). Adrenal cortex (males and females). Ovary and placenta Adrenal cortex (males and females). Ovary and placenta Adrenal cortex (males and females). Function 1) development of male sex organs 2) male secondary sex characters. 3) important for spermatogenesis 4) anabolic effect 1) development of female sex organs 2) female secondary sex characters 3) development of breast duct system 1) prepares the uterus for implantation of the ovum 2) stabilizes pregnancy 3) development of breast alveolar system 4) proliferative phase of the menstrual cycle 5) anabolic effect 4) secretory phase of the menstrual cycle 5) anabolic effect
B- Adrenal cortex hormones They are secreted from the adrenal cortex. They are classified into: glucocorticoids & mineralocorticoids
Examples Structure glucocorticoids corticosterone cortisol (OH at C11) 21 carbon Steroid nucleus Oxygen at C3 = between C4 and C5 2 CH3 at C10 and C13 Ketol group at C17 OH at C11 mineralocorticoids Aldosterone (OH at C11) 11-deoxy corticosterone 11-deoxy cortisol 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)
OH OH 11 deoxy corticosterone 11 deoxycortisol 25
Structure Adrenal cortical hormone Glucocorticoids 21 carbon Mineralocorticoid s 21 carbon Aldosterone 21 carbon Cortisol (17 hydroxy corticosterone) Ketol group at C17. (11 deoxy cortisol) No Oxygen at C11 Ketol group at C17. Aldosterone Aldehyde group at C13 Ketol group at C17. OH
Site of secretion Functions glucocorticoids Adrenal cortex. 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 mineralocorticoids Adrenal cortex. 1) sodium, chloride and water retention ( absorption). 2) potassium excretion (in the urine). Aldosterone is the most powerful mineralocorticoid
Lipid Chemistry Presented By Ayman Elsamanoudy Salwa Abo El-khair 7
Steroids C- 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.
+ glycine Glycocholate Na OR K glycocholate Cholic acid +taurine Taurochlate Na OR K taurocholate 35
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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. 37
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
Criteria of carotenes: 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. 39
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. 40
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 46
-One of the following steroids contains phenolic group: a) Testosterone. b) Cortisol. c) Estradiol. d) Progeterone 47
GREAT THANKS Ayman Elsamanoudy Salwa Abo El-khair 11/17/2014 Ahmed A.Albadry 48