LIPIDS Are organic substances made up of fatty acids and their naturally existing compounds and derivatives. a group of naturally occurring compounds, which have in common a ready solubility in such organic solvents as hydrocarbons, chloroform, benzene, ethers and alcohols. They include a diverse range of compounds, like fatty acids and their derivatives, carotenoids (yellow-red pigments found in plants) , terpenes (group of unsaturated HC, responsible for scent of plants/oils), steroids and bile acids.
LIPIDS Lipids are fatty acids and their derivatives, and substances related biosynthetically or functionally to these compounds.
are broadly defined as any fat-soluble (lipophilic), naturally-occurring molecules, such as fats, oils, waxes, cholesterol, steroids, fat-soluble vitamins (such as vitamins A, D, E and K), monoglyceride, diglyceride, phospholipids, and others.
Lipids may be defined according to whether they are: Esters or potential esters Soluble in fat solvent such as acetone , ether, chloroform, benzene, ether, hexane and methanol. Biologically active, that is, lipids are utilized by living organisms.
Characteristics Lipids refer to oils and fats and related compound. They constitute 2-25% of daily diet. They contain C, H2, O2, P and N They are insoluble in water but soluble in organic solvents.
Chemically they are esters of alcohols and fatty acids of high molecular weight. True fats generally constitute the storage material for energy in both plants and animals. Fat depot in animals derived from ingested foods are abundant in subcutaneous and intramuscular connective tissue.
Constitute a part of the cell wall and play a role in the permeability of cellular membranes.
Functions of Fats Major source of calorie energy especially fatty acids. Insulating material for internal organs Structural components of membrane Enzyme-co-factor (plays an essential role in the reaction) Vehicle for transport of fat soluble vitamins Regulatory substance Preventors of some steroid, prostaglandin hormone and Vit. D.
Important constituent of biomemebranes notably phospholipids, cholesterol and glycolipids. Thermal insulators in subcutaneous tissue and around certain organs. For transport or as carriers. Lipoprotein solubilize non polar and hydrophobic substances.
As precursor of other physiologically functional substances. Cholesterol is the precursor of bile acids and salts and steroidal hormones. As hormones. The prostaglandins derived from polyunsaturated fatty acids whose potent biological activities are regulatory in nature.
c Classification of LIPIDS I. SIMPLE LIPIDS – esters of fatty acids and glycerol with various alcohols and the yield on hydrolysis.A.Neutral Fats – glycerol esters of fatty acids a. oil – under ordinary conditions are liquid, made up of higher proportions of unsaturated fatty acids.
b. Fats – under ordinary conditions are solids,made up of greater percentage of saturatedFatty acids.B. Waxes – esters of fatty acids with monohydricalcohol both of higher molecular weight.
II. Compound LIPIDS – lipids in combination withother compounds which yields on hydrolysis of some other products beside alcohol and fatty acids.A.Phospholipid – contains H2PO4 and nitrogenous group. a. lecithin (phosphatidyl choline) contain choline as nitrogenous base. b. cephalin –( phosphatidyl ethanolamine) – contains ethanolamine/serine as nitrogenous base. c. Sphingomyelin – splingosine and choline are the nitrogenous base.
B. Glycolipids- contain carbohydrate andnitrogenous base without phosphorous andglycerol.C. Ill –defined lipids – amino acids and sulfolipidshaving amino and sulfate groups respectively. Alsoknown as sulfolipids.D. Lipoproteins – Those are lipids bound toproteins. Ex. Chylomicrons, VLDL, LDL and HDL.
III. Derived lipids – products of the decomposition of lipids like fatty acids and glycerol but still exhibiting the general physical characteristics of lipids.a. Saturated and unsaturated fatty acidsb. Mono and diglyceridesc. Alcohols 1.straight chain –products of hydrolysis of waxes usually water insoluble alcohol of higher molecular weight. 2. Alcohol containing beta-ionene ring – vitamin A and some carotenoids. 3. sterols
IV. Miscellaneous lipidsa. Alipathic HC – iso-ocatadane from liver, fats and certain hydrocarbons.b. Squalene HC – in shark , liver and human sebumc. Carotenoidsd. Fat soluble vitamins A,D,E,K.
Fatty acids (saturated and unsaturated) –product of fatty hydrolysisTypesSaturated fatty acids – belonging to the acetic acid series with empirical formula:CnH2n + 1 COOH or CnH2nO2
Name No. of C Chemical Sources atoms formulaStraight chain 4 C 4 H 8 O2 Butterbutyric acidCaproic acid 6 C6H12O2 Butter, coconut and palmCaprylic acid 8 C8H16O2 dittoCapric acid 10 C10H20O2 dittoLauric acid 12 C12H24O2 Laurel and coconut oil
Properties of Saturated Fatty acidsLow molecular weightSolid at ordinary temperatureLow melting pointVolatileNote those with 4 or less carbons are miscible with water in all proportions but as the chain increases, the solubility decreased proportionately.
Unsaturated fatty acids- unstable in air, the degree of unsaturation varies with the number of double bonds present in the structure.Empirical formula:CnH2n + 1-2m COOHWhere m stands for the number of double bonds
Name No. of Carbon Chemical Sources atoms formula1. Double bond 1 C16H31COOH Butter, fish oils,Palmitoleic 16 C18H35COOH hen fatOleic acid 18 Plant and animal fat, olive oil2. Double bonds 2 C18H33COOH Linseed oil, lard,Linoleic acid 18 cottonseed oil.3. Double bonds 5 C18H27COOH Linseed oil fishLinolenic acid 18 liver oil4. Double bonds 7 C20H27COOH Lecithin,Arachidonic acid 20 cephalin, butter, liver fat
Properties of unsaturated fatty acidsUnstable and reactive due to the presence of double bonds in their molecules.Reactivity increases with the increase of the double bonds degree of unsaturation.Insoluble in ordinary solventsLiquid at ordinary temperature, non-volatile.The greater the degree of unsaturation, the lower the melting points.
Free Fatty Acids (FFA, NEFA, UFA)Composed of carboxylic acid (COOH) with long hydrocarbon chains or R- COOH where the R maybe unsaturated (dehydrogenated with double bonds) or saturated (without double bonds) a. saturated fatty acids b. unsaturated fatty acids c. essential fatty acids
Essential fatty acids – are polyunsaturated fatty acids found in structural lipids which includes. a. linoleic acid b. linoleinic acid c. arachidonic acid
These fatty acids (saturated, unsaturated and essential ) must be present in diet to prevent: a. dermatitis b. poor growth c. decrease resistance to stress d. impaired lipid transport
Simple lipidsA. Fats (neutral fats)/ Tryglycerides/Triacylglycerol (TAG)- these are esters of alcohol glycerol and 3 fatty acids. They are neutral esters of monobasic fatty acids with trihydric alcohol, glycerol
Structure CH2-O-CO-R1 CH -O-CO-R2 CH2-O-CO-R3R with common fatty acid chain (simpletriacylglycerol)R with different fatty acid chain (mixedtriacylglycerol)
Naturally existing fats are usually of this type. They do not contain three molecules of the same fatty acids. There is always a mixture of acids. These explain the presence of different fats in different organs of the same animals.
Animal fats contains mostly: palmitic, oleic and stearic acids.Butter fat contains mostly: palmitic, oleic,and butyric and caproic acids in small amounts.Human fats is mostly oleic acid. It has a yellowish tinge due to carotene and xanthophyll pigments derived from ingested food.
TAG is divided into two groups: 1. fats 2. vegetable oils
Physiologic consideration1. These are esters of fatty acids and glycerol which is the main storage form of lipids (fats) in man.2. Stored fats are more efficient in its energy storage than carbohydrate, because: a. purity of storage-interaction of lipids and water are minimal, thus fats can be stored in its pure form (anhydrous).
b. unlimited storage – CHO can be stored chiefly in the liver and to a lesser extent skeletal muscle, whereas adipose tissues covers different parts of organs of the body.c. Greater ATP yield- the energy yield from complete oxidation of fatty acids is about 9cal/g in contrast to 4cal/g for CHO and CHON.
3. The TAG in adipose tissue are continuously undergoing hydrolysis and reesterification. The result of this determines the levels of FFA in the circulating plasma.4. Excessive CHO intake leads to lipogenesis and eventually obesity due to provision of substrate, cofactors and activation of lipogenetic enzymes in its metabolism.
B. Waxes - esters of fatty acids with certain alcohols-not glycerol and not the sterols.Properties:1. Insoluble in water and soluble in fat solvents.2. Not easily hydrolyzed as the fats are not digested by the fat splitting enzymes.
3. From the nutritional standpoints, they have so many uses from the economic viewpoint such as: a. In the manufacture of shoe polishes, varnish, candles, lubricants and cosmetics.
Examples:a. Bees wax – Secreted by the honey bee to form the comb. It is a mixture, the chief constituent being myricyl palmitate.b. Spermaceti wax- found in the skull of certain whales and dolphins it is chiefly cetyl palmitate and used in the manufacture of candles.c. Chinese wax/carhauba wax – derived from cuticle of the leaves.
Compound lipidsPHOSPHOLIPIDS- are compound lipids which contain the phosphate group. They also contain another non-lipid component. Choline, ethanolamine, amino acid serine or inositol. They are subdivided according to the alcohol which they contain.They are found in cells of both plants and animals.
Types of phospholipids1. lecithin/phosphatidyl choline a. present in great quantities in egg yolk, liver and nervous tissues. b. derived from the greek word lecithes meaning yolk. c. plays an important role in metabolism d. under physiologic condition lecithin occurs in the form of zwitter ion.
2. Cephalins/P. serine/ethanolamine a. nitrogenous base is either ethanolamine or serine. b. thromboplastic substance which initiates the process of coagulation. c. differs in lecithin only on it nitrogenous base. d. found in brain tissues and blood.
3. Sphingomyelin – most abundant sphingolipid. a. Phosphatides without glycerol components. b.Marked increase in the liver, spleen and tissues in case of Niemann-Pick’s disease. c. Fatty acids maybe lignoceric, stearic or nervonic acid.
GLYCOLIPIDS – occurs in nerve tissues, especially in the white matter of the brains so they are referred to as the cerebrosides. The well known cerebrosides are keratin, phrenosine, nervene and oxynervone.
Keratin – lignoceric acid, saturated fatty acids (may also be found in spleen and liver in Gaucher’s disease keratin is stored in along with other lipids in spleen and liver)Phrenosine – yields cerebronic acid and hydroxylignoceric acid
Oxynervone – oxynervone acid, unsaturated hydroxylignoceric acid Nervone – nervonic acid and unsaturated lignoceric acid present in nerves.
SULFOLIPIDS These are sulfuric acid esters of cerebrosides. The sulfate is joined as an ester to C-6 or C-3 of galactose. 20% of brain cerebrosides occur as sulfate esters.
Derived Lipids Products of decomposition of lipids like fatty acids and glycerol but still exhibiting the general physical characteristics of lipids.
Tarpenes – are class of compounds containing multiple of five carbon atoms so related to each other. It includes essential oils such as camphor, citral, plant pigments and vitamin A as well as squalene. Steroids – these constitutes a variety of compounds such as sterols, bile acids, sex hormones, fat soluble vitamin D. steroids are found in the non-saponifiable fraction of lipids. The basic steroid nucleus is called cyclopentanoperhydrophenanthrene(CPPP).
A. Sterols CHOLESTEROL Representative member of sterols. Normal product of animal metabolism. It is unsaturated alcohol with 27 carbons. Important because of its effect in the degenerative hardening of the arterial wall leading to arteriosclerosis.
Color reaction test Liebermann burchard test – test for determination of chollesterol in the blood. That yields into an emeral green color upon acted by chloroform, acetic anhydride and conc. Sulfuric acid.
Salkowski test – a test not specific for cholesterol but may also be used for other sterols. It yields a bluish red to purple color when cholesterol is treated with chloroform and concentrated sulfuric acid.
Other sterols 7-dehydrocholesterol – a precursor of cholesterol which is found underneath the skin. Ergosterol – the yeast sterol. Sitosterols – complex mixture of sterols occuring in oils and higher plants.
B. Bile acids Secreted continuously in the and stored in the gall bladder. It is discharged into bowel during digestion by the relaxation of the sphincter of the digestive organs and the relaxation of the gall bladder.
Functions of bile Emulsifying fats and preparing them for the action of trypsin. It aid in the digestion and absorption of fats. Excellent emulsifying agents. Excretion of certain waste products.
There are four acids that have been isolated in human bile like: Cholic acid Deoxycholic acid Chemodeoxycholic acid Lithocholic acid
They are conjugated to form bile salts. The two principal bile salts are: Sodium glycholate Sodium laurocholate They function in digestion, helps in emulsification of fats by lowering the surface tension of water.
Bile pigements (bilirubin and beliverdin) They give bile its characteristic color and are considered as excretory products. Oxidaton and reduction produce a series of various colored compounds some of which have received definite names: They derived from hemoglobin of worn out red blood cells.
Test for bile pigments Gmelin’s test – produces a rainbow or play of colors when bile reacted with concentrated nitric acid.
C. Steroidal hormones 1. Adrenocortical hormone . If the adrenal cortex is removed the animal dies. A partail loss of the function of the gland results in retention of K+, increased excretion of Na+ and Cl-, muscle weakness, decreased liver glycogen, lowered resistance to insulin and greater sensitivity to cold and stress
Addisons disease. Is a result of adrenocortical insufficiency and responds to treatment with extracts from adrenal cortex. ACTH. Is secreted by the pituitary. Stimulated the adrenal cortex to produce steroid hormone which in turn exert an inhibitory effect on the pituitary gland. These steroids contitutes a family of hormones of which cortisol and aldosterone are the major representative.
Functions of the ACTH 1. affects metabolism of the food stuff. 2. maintain proper balance of electrolytes and control inflammation. Adrenal hormones are used in the treatment of rheumatic fever, arthritis, acute asthma and a number of other ailments.
Prolonged used of cortisone can have serious side effects, some of which are characteristics of Cushing’s syndrome, a disease in which there is excessive production of adrenal steroids (including high blood pressure, wasting of muscle resorption of bones).
2. Sex Hormones. Both male and female sex hormones are steroids. The male hormone, androgens are the generic name for hormone secreted chiefly by the testes and responsible for the development of the secondary sexual characteristics. However these hormones are also produced in other tissues such as the adrenals and ovary.
Testosterone. Is the chief testicular androgen and is secreted by the leydig cells. In the female there are two types: estrogen and progesterone. There are three estrogens that have been identified.estradiol, estrone and estriol.
The estrogen controls the ovulation cycle. They undergo oxidation process in the liver and subsequently conjugate with sulfate and glucoronic acid in which they are excreted in the bile and urine. The progesterone is elaborated in the corpus luteum of the ovary during the post- ovulatory phase of the menstrual cycle and in much longer amount during gestation by both corpus luteum and placenta. They are required for normal pregnancy.
D. Fat soluble vitamins Vitamin A (retinol) Vitamin D (calciferol) Vitamin E (tocopherol) Vitamin K (coagulation vitamin)