Lec 2 1. Saponification number Definition : The number of m gms of KOH required to saponify the free and combined fatty acids in one gram of a given fat. Uses : The amount of alkali needed to saponify a given amount of fat will depend upon the number of COOH groups. Fat with high number of COOH groups take up more Na or K and give high saponification number.
Ex : Butter contain large proportion of short chains of fatty acids, so it has high saponification number while margarine with more long fatty acids, so it has low saponification number. 2. Iodine number: Number of grams of iodine taken up by 100 gm s of fat. Uses : To know the degree of unsaturation of fatty acids and it is directly proportional to the content of unsaturated fatty acids ex: butter is low iodine number while sun flower is high iodine number.
CH3- (CH2)7- CH=CH(CH2)7-COOH + I2 CH3- (CH2)7 CH-CH (CH2)7-COOH I I 3. Acid number: Number of m gms of KOH required to neutralize the fatty acids in a gram of fat Uses: to indicate the degree of rancidity of fat. 4. Formation of soaps: Hydrolysis of a fat by an alkali is called saponification, the product is glycerol and the alkali salts of the fatty acids are called soaps. 3RCOOH+ 3 NaOH - 3RCOONa + glycerol soaps =
Soaps are cleaning agents contain stearic, palmitic and oleic acids predominantly and large amount of sodium or potassium salts of these acids. Sodium soaps is hard, potassium soaps are soft but costly. To make the soap good lather even with hard water add Na2CO3 or silicate in small amounts.
Phospholipids Define as compound lipids contain in addition to fatty acids and glycerol, phosphoric acid and nitrogen base. Distriputed in animals in liver, brain, tissues, sperm and egg yolk. In plants it is present in seeds and sprouts. Classification: 1. Glycerophosphatides: alcohol is glycerol a. Phosphatidyl choline(lecithin) b.phosphatidyl ethanol amine (cephalin) c. Phosphatidyl serine ephalin) d. Plasmalogn
2. Phosphosphingosides: alcohol is sphingosine (sphingol). a) lecithin Functions: prevent accumulation of fat in the liver. Absence of cholin will block the synthesis of lecithin and thus the normal transportation of lipids to and from liver. Cholin is define as lipotropic factor convert of fat(triglyceride) to phospholipid, therefore prevent the condition of fatty liver. Triglyceride(TG) cholin Phospholipid
b) Phosphatidyl ethanolamine(cephalin) Structurally identical to lecithin except that base ethanolamine replaces cholin. It is rich in brain and nervous tissues. Functions: a. Important in the clotting of blood. b. sources of phosphoric acid for formation of new tissues.
c) Phosphatidyl serine: phospholipid contain amino acid serine in place of ethanol amine. d) Plasalogen: 10% of total phospholipids are concentrated in brain, nervous tissues, muscle and mitochondria.
Structurally like lecithin and cephalin except that the normal ester is replaced by the ether linkage on the carbon atom C1. The nitrogen base is cholin or ethanolamine. CH2-O-CH=CH-R1 I R2-C-O- CH O I II CH2-O-P-O-CH2-CH2-NH2 I OH
2. phosphosphigosides: ex: sphin gomylin found in large quantities in brain and nervous tissues. Consist of : fatty acid+ phosphoric acid+ nitrogen base choline + one molecule of complex amino alcohol called sphingosine (sphingol). Clinical aspect of sphingomylin is Niemann-Pick disease, inherited disorder of sphingomylin metabolim lead to accumulation of sphingomyline in liver, spleen and brain. It called lipid storage disease(lipidosis).
Functions of phospholipids 1. Role in enzyme action: Mitochondrial enzyme system involved in oxidative phosphorylation. 2.Role in blood coagulation. Convertion of prothrombin to thrombin by active factor. 3.Role in lipid absorption in intestine. Lecithine lowers the surfac tention of water and aids in emulsification of lipid water mixtures which help in absorption of lipids from gastrointestinal ( GI ) tract. 4. Role in transport of lipids from intestine. Exogenous T.G is carried as lipoprotein complex chylomicrons,in which P.L takes an active part. 5.Role in transport of lipids from liver. Endogenous TG is carried from liver to various tissues as lipoprotein complex called very low density lipoprotein (VLDL). 6. Lipotropic action of lecithin. Cholin in lecithin act as lipotropic agent prevent fatty liver formation.
Glycolipids: sphingosine Cerebrosides galactose Fatty acid Consist of fatty acid, alcohol (sphingosine) and sugar galactose. It is present in large quantities in brain especially in white matter.
Cholesterol 1. The word chol is derived from Greek words, cho bile, steros= solid, ol= alcohol 2. All steroids have cyclopentanophenanethrene ring (A,B,C and D) called steroid nucleus. Cholesterol is called sterols because it has hydroxyl group, while steroids contain ketone groups (C=O) or carboxyl group (COOH). 3. In 70 kg man a total of 140 g of cholesterol is available, which is distributed in brain, nerves, muscles, adipose tissues, skin, blood, liver, spleen, bone marrow, alimentary tract and adrenal gland and present in all cell membranes. 4. It is a light yellow crystalline solid.
Soluble in organic solvents Present as free and ester cholesterol Cholesterol ultraviolet Vit D3 Ergosterol is present in plants Ergosterol ultraviolet Vit D2
Sources of Cholesterol 1. Exogenous: dietary cholesterol about 0.3gm/day. Butter, cream, milk, egg yolk and meat are rich in cholesterol. 2. Endogenous: cholesterol is synthesized by all tissues such as liver,intestine,adrenal cortex,overies,tests and placenta. Cholesterol synthesis from acetyl COA.
1. Regulated of body fluids Functions of Cholesterol Cholesterol is esterified with essential fatty acids to form ester cholesterol, tend to lower the plasma bad cholesterol level. 2. Formation of Vit D3, bile acid and steroid hormones (testosteron, estradiol, progesterone). 3. Neutralize the hemolytic action of number of agents like snake venoms and bacterial toxins.
Elimination of cholesterol: Cholesterol is eliminated from the liver by converted to 1. bile acid and bile salts that are secreted into the intestinal lumen(duodenum). Serve as a component of lipoproteins sent to the peripheral tissues.
Plasma Lipoproteins: Lipoproteins are spherical macromolecular complexes of lipids and specific proteins(apoproteins) or (apolipoproteins). Types of lipoproteins: 1. Chylomicrons. 2. Very low density lipoproteins(vldl). 3. Low density lipoproteins(ldl). 4. High density lipoproteins(hdl).
They are differ in lipid and protein in: 1. Composition 2. size 3. density 4. site of origin. Composition of lipoproteins: Composed of neutral fat(tg) and cholesterol in the core surrounded by a shell of amphipathic apo proteins, phospholipids and free cholesterol.
1.Chylpmicrons: lipoprotein particales, large size, low density, contain highest percentage of lipid(90%) and lowest percentage of protein. Function: Transport of triglyceride(comes from diet) to adipose tissues for storage and to muscles or heart for energy needs. 2. Very low density lipoproteins(vldl). synthesis in liver, it contain about 60% of (TG), convert in to LDL in the capillaries.
Function: carry lipid (TG) synthesis in the liver to the peripheral tissues. The balance between synthesis of TG in the liver and secretion as VLDL cause Fatty liver. Causes of fatty liver: 1. obesity 2.uncontrolled diabetes mellitus 3. alcoholic ingestion.
3. Low density lipoprotein (LDL). Particales contain much less of TG than VLDL and have high concentration of free and ester cholesterol. Most of LDL derived from VLDL. Function: Transport of cholesterol from liver to the peripheral tissues. LDL concentration in the blood has positive correlation with incidence of cardiovascular disease, so it is highly atherogenic and called ( bad cholesterol).
4. High density lipoprotein (HDL). Particales formed from 70% of apo protein (APO -A1) made by the liver and intestine. Functions: transport cholesterol from tissues to the liver for synthesis of bile and to steroidogenic cells for hormone synthesis. HDL designation as the ( good cholesterol) carrier. It is antiatherogenic.
Methods used for separation of lipoproteins: 1. Ultracentrifugation. The separation of lipoproteins depend on their densities, lipoprotein which contain high amount of fat is less dense like chylomicron. Increase density with decrease amount of fat.
2. Electrophoresis The mobility of lipids depend on protein content. Particles with higher content of protein move faster towards anode(+). HDL is faster, then VLDL, LDL, chylomicron.
Bile acid Define as watery mixture of organic and inorganic compounds. Lecithin and bile salts are the most important organic components of bile. Bile synthesis in liver, then pass through bile duct to the duodenum for digestion and absorption of fat, or be stored in gallbladder when needed for digestion(not immediately).
Types of bile acids: 1. Primary bile acid: Synthesis in liver from cholesterol. ex: cholic acid 2. Secondary bile acid: produced in intestine from primary bile acids by the action of bacteria. ex: deoxycholic acid and lithocholic acid. Primary bile acid acts as emulsifying agents. Before bile acids leave the liver,they are conjugated with glycine or taurine producing bile salts glycocholic acid and taurocholic acid.
Note: If more cholesterol enters the bile than can be solubilized by the bile salts and lecithin present, then cholesterol precipitate in gallbladder lead to gall stone disease cholelithiasis.