CARBOHYDRATES notes.pdf

CARBOHYDRATES Sugar Pentoses of physiologic importance....

CARBOHYDRATES Sugar Pentoses of physiologic importance. Where Found Biochemical Importance Clinical Significance CLASSIFICATION: Base on MOLECULAR SIZE D-Ribose Nucleic acids Structural elements of nucleic (DNA acids and coenzymes, eg, ATP, MONOSACCHARIDE sugar) NAD, NADP, flavoproteins. - is a carbohydrate that contains a single polyhydroxy aldehyde or polyhydroxy Ribose phosphates are ketone unit. intermediates in pentose - cannot be broken down into simpler units by hydrolysis reactions phosphate pathway - Naturally occurring monosaccharides have from three to seven carbon atoms; five- and six-carbon species are especially common. D-Ribulose Formed in metabolic Ribulose phosphate is an - Pure monosaccharides are water-soluble, white, crystalline solids. processes. intermediate in pentose phosphate pathway. Tabulation of biochemically important MONOSACCHARIDES D- Gum arabic. Plum and Constituent of glycoproteins. Arabinose cherry gums. C atoms RCHO RCOR RCHO RCOR D-Xylose Wood gums, Constituent of glycoproteins. 3 (C3H6O3) triose triulose glyceraldehyde dihydroxyacteone (aka wood proteoglycans, sugar) glycosaminoglycans. 4 (C4H8O4) tetrose tetrulose -Erythrose -Erythroluse -Threose D-Lyxose Heart muscle. A constituent of a lyxoflavin isolated from human heart 5 (C5H10O5) pentose pentulose -Ribose -Ribulose muscle. -Arabinose -Xylose -Xylulose L-Xylulose Intermediate in uronic Found in urine -Lyxose acid pathway. in essential 6 (C6H12O6) hexose hexulose -Allose -Psicose pentosuria. -Altrose -Fructose -Glucose -Sorbose 5C Ribose -Mannose -Gulose -Idose D-Ribose -Galactose - a component of ribonucleic acids (RNAs) and energy-rich compounds such as adenosine -Talose triphosphate (ATP). - The compound 2-deoxy-D-ribose is also important in nucleic acid chemistry. This monosaccharide is a component of DNA molecules. 3C D-Glyceraldehyde & Dihydroxyacetone - The prefix deoxy- means “minus an The simplest of the monosaccharides, these two trioses are important intermediates in the oxygen”; the structures of ribose and 2- process of glycolysis, a series of reactions whereby glucose is converted into two deoxyribose differ in that the latter molecules of pyruvate. D-Glyceraldehyde is a chiral molecule, but dihydroxyacetone is not. compound lacks an oxygen atom at D-glyceraldehyde Structure Dihydrocyacetone Has chiral carbon or center Does not possess chiral carbon or center D- Ribose is a pentose. D-glucose, D-galactose, and D-fructose are all L and D forms are possible L and D form is not possible hexoses If carbon 3 and its accompanying -H and -OH groups were eliminated Aldose Ketose from the structure of D-glucose, the remaining structure would be that of D-ribose  Hexoses of physiologic importance 6C Galactose Sugar Source Importance Clinical Significance D-Galactose D-Glucose Fruit juices. The “sugar” of the body. Present in the urine -is synthesized from glucose in the mammary glands for use in lactose (milk sugar), a (Grape Hydrolysis of The sugar carried by the (glycosuria)in diabetes disaccharide consisting of a glucose unit and a galactose unit sugar, starch, cane sugar, blood, and the principal mellitus owing to - sometimes called brain sugar because it is a component of glycoproteins found dextrose, maltose, and one used by the tissues raised blood glucose in brain and nerve tissue. blood lactose. (hyperglycemia). - D-Galactose is also present in the chemical markers that distinguish various types of sugar) blood—A, B, AB, and O D-Galactose and D-glucose are epimers (diastereomers that differ D-Fructose Fruit juices. Honey. Can be changed to glucose Hereditary fructose only in the configuration at one chiral center) (levulose, Hydrolysis of cane in the liver and so used in intolerance leads to fruit sugar, sugar and of inulin the body. fructose accumulation two compounds differ only in the configuration of the –OH group dietary (from the and hypoglycemia. and -H group on carbon 4. sugar) Jerusalem artichoke). Epimers are diastereomers whose molecules differ only in the D- Hydrolysis of - Can be changed to Failure to metabolize configuration at one chiral center. Galactose lactose. glucose in the liver and leads to galactosemia (brain (disaccharide metabolized. Synthesized and cataract sugar) consisting of a in the mammary gland to 6C Fructose glucose unit and a make the lactose of milk. A galactose unit) constituent of glycolipids D-Fructose and glycoproteins (present - D-Fructose is biochemically the most important ketohexose. It is also known as in the brain) levulose and fruit sugar. - chemical markers that - used as a dietary sugar not because it has fewer calories per gram than other distinguish various types sugars but because less is needed for the same amount of sweetness. of blood—A, B, AB, and O D-Mannose Hydrolysis of plant A constituent of many mannans and glycoproteins. From the third to the sixth carbon, the structure of D- gums. fructose is identical to that of D-glucose. Differences at carbons 1 and 2 are related to the presence of a ketone group in fructose and of an aldehyde group in glucose. 6C Glucose D-Glucose (Aka dextrose, blood sugar, grape sugar) D- fructose Structure D-glucose Of all monosaccharides, D-glucose is the most abundant in nature and the most Hexose Hexose important from a human nutritional standpoint. D-Glucose tastes sweet, is nutritious. L-Glucose, on the other hand, is tasteless, Ketose Aldose and the body cannot use it. dextrose draws attention carbons 1 and 2 carbons 1 and 2 are to the fact that the optically are related to the related to the presence of active D-glucose, in presence of a an aldehyde group aqueous solution, rotates ketone group in glucose. Identical plane-polarized light to the right. fructose. structure from C3-C6 Identical structure from blood sugar draws attention to the fact that blood contains dissolved glucose. The normal concentration of glucose in human blood is in the range of 70–100 mg/dL (1 dL = 100 mL). C3-C6 DISACCHARIDE Properties Reducing Reducing sugar Reducing sugar Non-reducing sugar - carbohydrate that contains two monosaccharide units sugar bec. 1 -has 3 isomeric (glucose ring can -No free hemiacetal or unit of glucose form open to give an hemiketal moities - covalently bonded to each other has a aldehyde or has free -The hemiacetal center - crystalline, water-soluble substances hemiacetal hemiacetal glucose (anomeric carbon atom) of - Example: Sucrose (table sugar) and lactose (milk sugar) carbon (C1) unit) each monosaccharides is - Hydrolysis of a disaccharide produces two monosaccharide units. Forms: -form is sweeter involved in glycosidic a-maltose than & more water linkage results to 2 Two monossacharides are bonded together by a glycosidic bond B-maltose soluble than -form. hemiacetal center Open chain -form is present form with long stored ice cream producing a gritty crystalized texture. Reaction Maltase Cellobiase Hydrolysis of lactose Sucrase use to break ,(1- of causing by the enzyme 2) glycosidic linkage of Enzymes hydrolysis (or lactase forms units glucose to form equimolar in an acidic of --D-galactose & mic=xture of glucose and condition) -D- glucose fructose 2 glycosidic linkage is the bond in a disaccharide resulting from the reaction between the D-Glucose Maltose hemiacetal carbon atom -OH group of one monosaccharide and an -OH group on the other monosaccharide - malt sugar, one-third as sweet as sucrose, is produced whenever the polysaccharide starch breaks down, as happens in plants when seeds germinate Tabulation of Common DISACCHARIDES and in human beings during starch digestion. Feature Maltose Cellobiose Lactose Sucrose - It is a common ingredient in baby foods and is found in malted milk. Malt Common Malt sugar (1/3 Cellobiose Milk sugar Table sugar (germinated barley that has been baked and ground) contains maltose. Names as sweet - an interesting compound because of its use in alcohol production as sucrose) (fermentation). Source Digestion by Intermediate in Milk. May occur in Juice of sugar cane (20% by amylase or the hydrolysis of urine during mass) & sugar beets (17% hydrolysis of polysaccharide pregnancy. by mass) starch. cellulose Clinical significance: Clinical significance: Germinating In lactase deficiency, In sucrase deficiency, cereals and Nursing mother malabsorption leads malabsorption leads to malt. =7-8% to diarrhea and diarrhea and flatulence. Cow’s milk = 4-5% flatulence Structural 2 Glucose units 2Glucose units --D-galactose & --D glucose & Units - -D glucose --D-glucose & -D- glucose --D- fructose Maltose is a reducing sugar & -D- glucose - D-glucose Glycosidic (1-4) (head to (1-4) (head to (1-4) (head to tail) ,(1-2) OH group of C2 of Linkage tail) tail) Fructose(hemiacetal) + OH group on C1 of D-glucose (hemiacetal) (head to head)  2 D-Glucose Cellobiose In people with this condition, galactose and its toxic metabolic derivative galactitol (dulcitol) accumulate in the blood. Like maltose, cellobiose contains two D-glucose monosaccharide units. It differs from - can cause mental retardation in infants and even death maltose in that one of the D-glucose units—the one functioning as a hemiacetal—must have a or b configuration instead of the a-configuration for maltose. This change in D-Fructose configuration results in a b(1 : 4) glycosidic linkage. D-Glucose Sucrose Composed of a-D-glucose and b-D- fructose. table sugar, is the most abundant of all disaccharides and occurs throughout the plant kingdom The glycosidic linkage is not a (1 : 4) linkage, as was the case for maltose, cellobiose, and lactose. It is instead an a, b(1 : 2) glycosidic linkage. The - OH group on carbon 2 of D-fructose (the hemiacetal carbon) reacts with the -OH group on carbon 1 of D-glucose (the hemiacetal D-Galactose carbon). D-Glucose Lactose milk sugar (major sugar found in milk) Uses: ingredient in infant formulas that are designed to simulate mother’s milk. Sucrase, the enzyme needed to break the a, b(1 : 2) linkage in sucrose, is -LACTOSE AS AN EXCIPIENT used as a filler or filler- present in the human body. Sucrose hydrolysis (digestion) produces an equimolar mixture binder. of glucose and fructose called invert sugar. -cost effectiveness; When sucrose is cooked with acid-containing foods such as fruits or berries, partial -availability; hydrolysis takes place, forming some invert sugar. Jams and jellies prepared in this -bland taste; manner are actually sweeter than the pure sucrose added to the original mixture because -low hygroscopicity; one-to-one mixtures of glucose and fructose taste sweeter than sucrose. -compatibility with active ingredients and other excipients; -excellent physical and chemical stability; Changing Sugar Patterns: - water solubility 1. H F C S / High-fructose corn syrup - sweetener for food and beverages Conditions associated with Lactose A. HFCS42 1. Lactase persistence - used to describe the condition where milk-drinking ability B. HFCS90 continues into adulthood. C. HFCS55 2. Lactose intolerance- a condition in which people lack the enzyme lactase, which is 2. Sugar substitutes of sucrose needed to hydrolyze lactose to galactose and glucose. - saccharin Causes: - sodium cyclamate  Genetic defect - aspartame (nutra sweet)  Physiological decline w/ age 3. Derivatives of sucrose  Injury to the mucosal lining of the intestines a. Sucralose - is synthesized from sucrose by substitution of three chlorine 3. GALACTOSEMIA- caused by the absence of one or more of the enzymes needed for the atoms for hydroxyl groups. conversion of galactose to glucose. - heatstable - 600x sweeter than sucrose - calorie free  b. neotame- an aspartame derivative. The same two amino acids are present as POLYSACCHARIDE in aspartame. It differs structurally from aspartame in that a 3,3-dimethylbutyl is a polymer that contains many monosaccharide units bonded to each other by glycosidic group is attached to the terminal -NH2 group of aspartame. This “bulky” linkages. attachment prevents the breakdown of neotame into its component amino - Glycan- an alternate name for a polysaccharide. acids, as occurs for aspartame. Hence individuals with PKU can use neotame are called complex carbohydrates, simple carbohydrates for mono & disaccharides. without concern. Characteristic: - 7000x sweeter than sucrose 1. polysaccharides are not sweet and do not test positive in Tollens and Benedict’s solutions. OLIGOSACCHARIDES 2. They have limited water solubility because of their size. However, the - OH are carbohydrates that contain three to ten monosaccharide units bonded to each other groups present can individually become hydrated by water molecules. The result via glycoside linkages is usually a thick colloidal suspension of the polysaccharide in water. Two naturally occurring oligosaccharides in onions, cabbage, broccoli, brussel sprouts, 3. Polysaccharides, such as flour and cornstarch, are often used as thickening whole wheat, and all types of beans: agents in sauces, desserts, and gravy. a. Raffinose - trisaccharide, galactose, glucose, and fructose. b. Stachyose - tetrasaccharide , galactose, glucose, and fructose with Important parameters that distinguish various polysaccharides (or glycans) from each additional galactose other are: Humans lack the digestive enzymes necessary to metabolize either raffinose or stachyose. 1. The identity of the monosaccharide repeating unit(s) in the polymer chain. Hence these oligosaccharides, when ingested in food, pass undigested into the large a. homopolysaccharide is a polysaccharide in which only one type of intestine causing discomfort. monosaccharide monomer is present. examples: starch, glucan, glycogen, cellulose, and chitin c. Solanine, a toxin found in the potato plant , is another example of an oligosaccharide- b. heteropolysaccharide is a polysaccharide in which more than one (usually two) containing “complex” molecule. type of monosaccharide monomer is present. - alkaloid and trisaccharides of examples: hyaluronic acid and heparin b-l-rhamnose, 2. The length of the polymer chain. b-d-glucose, 3. The type of glycosidic linkage between monomer units b-d-galactose 4. The degree of branching of the polymer chain. Blood Types and Oligosaccharides Division of polysaccharides according to importance: Biochemical markers - oligosaccharide molecules that are attached to the plasma Storage Polysaccharides (Starch and Glycogen) membrane of red blood cells Structural Polysaccharides (Cellulose and Chitin) Acidic Polysaccharides (Hyaluronic acid and heparin) The absence or presence of a fifth monosaccharide Storage Polysaccharides (attached to the second is a polysaccharide that is a storage form for monosaccharides and is used as an energy galactose) determines blood source in cells. type. Type O blood lacks a Starch - a homopolysaccharide containing only glucose monosaccharide units. fifth monosaccharide unit. - It is the energy-storage polysaccharide in plants. Type A blood has N- - aka amylum acetylgalactosamine as a fifth unit. Type B blood has galactose as a fifth unit. Type AMYLOSE AMYLOPECTIN AB blood contains both type A and type B markers straight-chain glucose polymer, usually accounts a branched glucose polymer, accounts for the for remaining 15%–20% of the starch 80%–85% of the starch. - More water soluble because of increase in branching glucose units are connected by (1 : 4) glycosidic both (1 : 4) and (1 : 6) linkages. Glycogen USE: - is a branched polysaccharide containing only glucose units.  blood anticoagulant. It is naturally present in mast cells and is released at the site - it is the glucose storage polysaccharide in humans and animals and sometimes of tissue injury. referred to as animal starch.  It prevents the formation of clots in the blood and retards the growth of existing - Liver cells and muscle cells are the storage sites for glycogen in humans. clots within the blood. It does not, however, break down clots that have already formed. The glucose polymers amylose, amylopectin,and glycogen compare as follows in  The source for pharmaceutical heparin is intestinal or lung tissue of slaughter- molecular size and degree of branching. house animals (pigs and cows).  Amylose: Up to 1000 glucose units; no branching  Amylopectin: Up to 100,000 glucose units; Hormonal Control of Carbohydrate Metabolism - branch points every 25–30 glucose units Insulin  Glycogen: Up to 1,000,000 glucose units;  Insulin, a 51-amino-acid protein hormone produced by the beta cells of the - highly branch points every 8–12 glucose units pancreas.  promotes the uptake and utilization of glucose by cells. Thus its function is to These two opposing processes are called glycogenesis and glycogenolysis, the formation lower blood-glucose levels. and decomposition of glycogen, respectively.  It is also involved in lipid metabolism.  The release of insulin is triggered by high blood-glucose levels. Structural Polysaccharides  The mechanism for insulin action involves insulin binding to protein receptors on is a polysaccharide that serves as a structural element in plant cell walls and animal the outer surfaces of cells, which facilitates entry of glucose into the cells. Insulin exoskeletons also produces an increase in the rates of glycogenesis, glycolysis, and fatty acid Cellulose – Gossypium hirsatum synthesis. -the structural component of plant cell walls,  Insulin is at the core of the metabolic disorder known as diabetes; either the -is the most abundant naturally occurring polysaccharide. body does not produce enough insulin or body cells do not respond properly to -the “woody” portions of plants—stems, stalks, and trunks—have particularly high the insulin that is produced. concentrations of this fibrous, water-insoluble substance. - Like amylose(a-1:4), cellulose (b-1:4)is an unbranched glucose polymer Chitin Glucagon The 2nd most abundant naturally occurring polysaccharide, next to cellulose. Its function  Glucagon is a polypeptide hormone (29 amino acids) produced in the pancreas is to give rigidity to the exoskeletons of crabs, lobsters, shrimp, insects, and other by alpha cells. arthropods. It also has been found in the cell walls of fungi.  It is released when blood-glucose levels are low. - contains galacturonic acid which is not found in cellulose  Its principal function is to increase blood-glucose concentrations by speeding up the conversion of glycogen to glucose (glycogenolysis) and gluconeogenesis in Acidic Polysaccharides the liver. Thus glucagon’s effects are opposite those of insulin.  polysaccharide with a disaccharide repeating unit in which one of the disaccharide components is an amino sugar and one or both disaccharide components has a Epinephrine negative charge due to a sulfate group or a carboxyl group.  Epinephrine , also called adrenaline, is released by the adrenal glands in  are heteropolysaccharides; two different monosaccharides are present in an response to anger, fear, or excitement. alternating pattern  Its function is similar to that of glucagon— stimulation of glycogenolysis, the Hyaluronic Acid release of glucose from glycogen.  contains alternating residues of N-acetyl-b-Dglucosamine (NAG) and D-  Its primary target is muscle cells, where energy is needed for quick action. Glucuronate.  It also functions in lipid metabolism. USES:  Highly viscous hyaluronic acid solutions serve as lubricants in the fluid of joints,  are also associated with the jelly-like consistency of the vitreous humor of the eye. (The Greek word hyalos means “glass”; hyaluronic acid solutions have a glass-like appearance.) Heparin  small highly-sulfated polysaccharide with only 15–90 disaccharide residues per chain