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CARBOHYDRATES & LIPIDS CARBOHYDRATES CARBOHYDRATES ARE ALDEHYDE OR KETONE DERIVATIVES OF POLYHYDRIC ALCOHOLS ;CLASSIFIED AS MONO,DI,OLIGO &POLY. 1.Monosaccharides The monosaccharide commonly found in humans are classified according to the number of carbons they contain in their backbone structures. Classifications ALDOSES KETOSES Trioses (C3H6O3) Tetroses (C4H8O4) Pentoses (C5H10O5) Hexoses (C6H12O6) Heptoses (C7H14O7) Glycerose (glyceraldehyde) Erythrose Dihydroxy acetone Erythrulose Ribose Ribulose Glucose Fructose — Sedoheptulose GLUCOSE Straight chain Haworth projection chair Hemiacetal;reaction between aldehyde and hydroxy grp. Epimers: Isomers differing as a result of variations in configuration of the —OH and —H on carbon atoms 2, 3, and 4 of glucose are known as epimers. 4th is Galactose , glucose , 2nd mannose. Pentoses of Physiologic Importance. Sugar Source Biochemical and Clinical Importance D-Ribose Nucleic acids and metabolic intermediate Structural component of nucleic acids and coenzymes, including ATP, NAD(P), and flavin coenzymes D-Ribulose Metabolic intermediate Intermediate in the pentose phosphate pathway D- Plant gums Constituent of glycoproteins D-Xylose Plant gums, proteoglycans, glycosaminoglycans Constituent of glycoproteins L-Xylulose Metabolic intermediate Excreted in the urine in essential pentosuria Arabinose Hexoses of Physiologic Importance. Sugar Source Biochemical Importance Clinical Significance D-Glucose Fruit juices, hydrolysis of starch, cane or beet sugar, maltose and lactose The main metabolic fuel for tissues; "blood sugar" Excreted in the urine (glucosuria) in poorly controlled diabetes mellitus as a result of hyperglycemia D-Fructose Fruit juices, honey, hydrolysis of cane or beet sugar and inulin, enzymic isomerization of glucosesyrups for food manufacture Readily metabolized either via glucoseor directly Hereditary fructose intolerance leads to fructose accumulation and hypoglycemia D- Hydrolysis of lactose Readily metabolized to glucose; synthesized in the mammary gland for synthesis of lactose in milk. A constituent of glycolipids and glycoproteins Hereditary galactosemia as a result of failure to metabolize galactose leads to cataracts Hydrolysis of plant mannan gums Constituent of glycoproteins Galactose D- Mannose Glycosides formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide, and a second compound that may or may not (in the case of an aglycone) be another monosaccharide. aglycone (methanol, glycerol, sterol, phenol, N base;amine-N-glycosidic bond) Important glycosides cardiac glycosides( contain steroids as the aglycone) derivatives of digitalis and strophanthus such as ouabain Streptomycin Phlorhizin DISACCHARIDES Sugar Source Isomaltose Enzymic hydrolysis of starch (the branch points in amylopectin) Maltose Enzymic hydrolysis of starch (amylase); germinating cereals and malt syl-(1 l-(1 Clinical Significance Lactose Milk (and many pharmaceutical preparations as a filler) Lack of lactase (alactasia) leads to lactose intolerance—diarrhea and flatulence; may be excreted in the urine in pregnancy Lactulose Heated milk (small amounts), mainly synthetic Not hydrolyzed by intestinal enzymes, but fermented by intestinal bacteria; used as a mildosmotic laxative Sucrose Cane and beet sugar, sorghum and some fruits and vegetables Rare genetic lack of sucrase leads to sucrose intolerance—diarrhea and flatulence Trehalose Yeasts and fungi; the main sugar of insect hemolymph Polysaccharides Serve Storage & Structural Functions Starch homopolymer, called a glucosan or glucan. most important dietary source of carbohydrate. constituents are amylose (13–20%), nonbranching helical structure, and amylopectin (80–85%), Glycogen storage polysaccharide. D-glucopyranose residues (in 1 4 glucosidic linkage) with branching by means of 1 6 glucosidic bonds . Inulin polysaccharide of fructose ,used to determine the glomerular filtration rate, Dextrins are intermediates in the hydrolysis of starch. Cellulose insoluble -D-glucopyranose 1 4 bonds cross-linking hydrogen bonds. Chitin exoskeleton of crustaceans and insects. GLYCOSAMINO GLYCANS LARGE COMPLEX OF NEGATIVELY CHARGED HETEROPOLY SACCHARIDE CHAINS. •ASSOCIATED WITH SMALL AMOUNT OF PROTEINS FORMING PROTEOGLYCAN •ALONG WITH COLLAGEN IT FORMS EXTRACELLULAR MATRIX [ ACIDIC SUGAR – AMINO SUGAR] – N ACIDIC SUGAR : AMINO SUGAR: •D – GLUCURONIC ACID •L – IDURONIC ACID •D – GLUCOSAMINE •D - GALACTOSAMINE ACIDIC SUGAR: SULPHATE & COOH – GIVE NEGATIVE GHARGE *KERATAN SULPHATE HAS GALACTOSE INSTEAD OF ACIDIC SUGAR AMINO SUGAR MAY BE SULPHATED ON C4 OR 6 ON NON ACETYLATED N REPELLING PROPERTY OF HETEROPOLY SACCHARIDES THE HETEROPOLYSACCHARIDES REPEL EACH OTHER AND REMAIN HYDRATED CONTRIBUTES TO THE RESILIENCE OF SYNOVIAL FLUID AND VITRIOUS HUMOR COVALENT ASSOCIATION IS FOUND BETWEEN GLYCANS AND PROTEINS EXCEPTION : HYALURONIC ACID CARTILAGE: PROTEOGLYCAN MONOMER (CONDROITIN SULPHATE) (KERATAN SULPHATE) SOME PROTEOGLYCANS SYNDECAN INTEGRAL MEMBRANE VERSICAN EXTRACELLULAR } AGGRECAN NEUROCAN CEREBROCAN } CNS LINKAGE Galactose – galactose – xylose – Serine { O – GLYCOSIDIC BOND BETWEEN xylose & OH of Serine PROTEOGLYCAN AGGREGATES Proteoglycan monomers associated with hyaluronic acid * GAG are given as supplements in cartilage associated diseases. Lipids Lipids Fatty Acids Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 17 Lipids Are, • biomolecules that contain fatty acids or a steroid nucleus. • soluble in organic solvents, but not in water. • named for the Greek word lipos, which means “fat.” • extracted from cells using organic solvents. 18 Types of Lipids The types of lipids containing fatty acids are • waxes • fats and oils (triacylglycerols) • glycerophospholipids • prostaglandins The types of lipids that do not contain fatty acids are • steroids 19 Fatty Acids Fatty acids are • long-chain carboxylic acids. • typically 12-18 carbon atoms. • insoluble in water. • saturated or unsaturated. Olive oil contains 84% unsaturated fatty acids and 16% saturated fatty acids 21 Saturated and Unsaturated Fatty Acids Fatty acids are • saturated with all single C–C bonds. • unsaturate d with one or more double C=C bonds. O C OH palmitic acid, a saturated acid O C OH palmitoleic acid, an unsaturated acid 22 Properties of Saturated Fatty Acids Saturated fatty acids • contain only single C–C bonds. • are closely packed. • have strong attractions between chains. • have high melting points. • are solids at room temperature. COOH COOH COOH 23 Properties of Unsaturated Fatty Acids • contain one or more cis double C=C bonds. • have “kinks” in the fatty acid chains. • do not pack closely. • have few attractions between chains. • have low melting points. • are liquids at room temperature. HOOC H H C COOH C “kinks” in chain H C C H 24 Melting Points of Some Fatty Acids 25 Lipids Waxes, Fats, and Oils 26 Waxes • esters of saturated fatty acids and longchain alcohols. • coatings that prevent loss of water by leaves of plants. 27 Fats and Oils: Triacylglycerols • also called triacylglycerols. • esters of glycerol. • produced by esterification. • fFormed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids. 28 Triacylglycerols In a triacylglycerol, glycerol forms ester bonds with three fatty acids. 29 Formation of a Triacylglycerol glycerol + three fatty acids triacylglycerol O CH2 OH CH OH CH2 OH + HO C O (CH2)14CH3 HO C O (CH2)14CH3 HO C (CH2)14CH3 O CH2 O C (CH2)14CH3 O CH O C (CH2)14CH3 + 3H2O O CH2 O C (CH2)14CH3 30 Melting Points of Fats and Oils A fat • is solid at room temperature. • is prevalent in meats, whole milk, butter, and cheese. An oil • is liquid at room temperature. • is prevalent in plants such as olive and safflower. 31 Oils with Unsaturated Fatty Acids Oils • have more unsaturated fats. • have cis double bonds that cause “kinks” in the fatty acid chains. • with “kinks” in the chains do not allow the triacylglycerol molecules to pack closely. • have lower melting points than saturated fatty acids. • are liquids at room temperature. 32 Diagram of Triacylglycerol with Unsaturated Fatty Acids Unsaturated fatty acid chains with kinks cannot pack closely. 33 Percent Saturated and Unsaturated Fatty Acids In Fats and Oils 34 Lipids Chemical Properties of Triacylglycerols 35 Chemical Properties of Triacylglycerols The chemical reactions of triacylglycerols are similar to those of alkenes and esters. • In hydrogenation, double bonds in unsaturated fatty acids react with H2 in the presence of a Ni or Pt catalyst. • In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme. 36 Hydrogenation of Oils • adds hydrogen (H2) to the carbon atoms of double bonds. • converts double bonds to single bonds. • increases the melting point. • produces solids such as margarine and shortening. 37 Hydrogenation O CH2 O C Ni (CH2)5CH CH(CH2)7CH3 O CH +O3HC2 (CH ) CH 2 5 O CH(CH2)7CH3 O CH2 O C CH2 O CH (tripalmitolean) (CH2)14CH3 O (CH2)5CH CH(CH2)7CH3 glyceryl tripalmitoleate C CH2 O O C (CH2)14CH3 O C (CH2)14CH3 glyceryl tripalmitate (tripalmitin) 38 Olestra, A Fat Substitute Olestra is • used in foods as an artificial fat. • sucrose linked by ester bonds to several long-chain fatty chains. • not broken down in the intestinal tract. 39 Cis and Trans Fatty Acids Unsaturated fatty acids can be • cis with bulky groups on same side of C=C. CH3─ (CH2)5 (CH2)7─ COOH cis C=C H H • trans have bulky groups on opposite sides of C=C. CH3─ (CH2)5 H C=C H (CH2)7─ COOH 40 Hydrogenation and Trans Fatty Acids Most naturally occurring fatty acids have cis double bonds. • During hydrogenation, some cis double bonds are converted to trans double bonds. • In the body, trans fatty acids behave like saturated fatty acids. • It is estimated that 2-4% of our total Calories is in the form of trans fatty acid. • Several studies reported that trans fatty acids raise LDL-cholesterol and lower HDLcholesterol. 41 Learning Check (1) True or (2) False A. There are more unsaturated fats in vegetable oils. B. Vegetable oils have higher melting points than fats. C. Hydrogenation of oils converts some cisdouble bonds to trans- double bonds. D. Animal fats have more saturated fats. 42 Solution (1) True or (2) False A. T There are more unsaturated fats in vegetable oils. B. F Vegetable oils have higher melting points than fats. C. T Hydrogenation of oils converts some cis-double bonds to trans- double bonds. D. T Animal fats have more saturated fats. 43 Hydrolysis • triacylglycerols split into glycerol and three fatty acids. • an acid or enzyme catalyst is required. O CH2 CH CH2 O O O C O (CH2)14CH3 C (CH2)14CH3 + H2O O C (CH2)14CH3 H+ CH2 OH CH OH CH2 OH O + HO C (CH2)14CH3 44 Cholesterol Cholesterol • is the most abundant steroid in the body. • has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus. CH3 CH3 CH3 CH3 CH3 HO 45 Cholesterol in the Body • is obtained from meats, milk, and eggs. • is synthesized in the liver. • is needed for cell membranes, brain and nerve tissue, steroid hormones, and Vitamin D. • clogs arteries when high levels form plaque. A normal, open artery. An artery clogged by cholesterol plaque 46 Cholesterol in Foods • is considered elevated if plasma cholesterol exceeds 200 mg/dL. • synthesized in the liver and obtained from foods. Not found in Plant foods 47 Lipoproteins • combine lipids with proteins and phospholipid s. • soluble in water because the surface consists of polar lipids. 48 Types of Lipoproteins • differ in density, composition, and function. • include low-density lipoprotein (LDLs) and high-density lipoprotein (HDLs). 49