Carbohydrates Types, Structure, Composition and Uses PDF

CARBOHYDRATES TYPES, STRUCTURE, COMPOSITION AND USES COMPILED AND ARRANGED BY JUSTIN RACHELLE P. DIMAGUIBA LEARNING OUTCOMES 1. Distinguish different types of carbohydrates based on their functional group, the number of carbons and sugar units and according to form; 2. Descri...

CARBOHYDRATES TYPES, STRUCTURE, COMPOSITION AND USES COMPILED AND ARRANGED BY JUSTIN RACHELLE P. DIMAGUIBA LEARNING OUTCOMES 1. Distinguish different types of carbohydrates based on their functional group, the number of carbons and sugar units and according to form; 2. Describe biochemical and physiological functions of carbohydrates.  Carbohydrates - The most abundant organic compounds in nature (50% of the earth’s biomass). - 3/4 of the weight of plants. - 1% of the weight of animals and humans (they do not store). - 65% of the foods in our diet -Found in the DNA as ribose Approximate ratio of CARBOHYDRATE molecule Carbon, hydrogen, oxygen 1 : 2 : 1 CARBOHYDRATE CLASSIFICATION  Carbohydrates H+ or enzyme 1. Monosaccharide + H2O no hydrolysis H+ or enzyme 2. Disaccharide + H2O two monosaccharide units + H+ or enzyme 3. Polysaccharide + many H2O many monosaccharide units  ALPHA VS BETA CARBOHYDRATES β 1 1 α α-D-Glucose β-D-Glucose Cyclic Structure – Haworth Structure Humans have α-amylase (an enzyme) and they can digest starch products such as pasta (contain α-glucose) Humans do not have β-amylase (an enzyme) and they cannot digest cellulose such as wood or paper (contain β-glucose)  Chirality All carbohydrates have 1 or more chirality centers. Glyceraldehyde, the simplest aldose, has one chirality center, and has two possible enantiomers.  Fischer Projections - Horizontal lines represent bonds projecting forward from the stereocenter. - Vertical lines represent bonds projecting to the rear. - Only the stereocenter (tetrahedral carbon) is in the plane. CHO Convert to Fischer CHO Projection H C OH H OH CH2 OH CH2 OH 2D 3D  Fischer Projections 1. Carbon with four different groups bonded to it. 2. The chiral carbon furthest from the carbonyl group (-CHO). * * * * * * * H * H O D - glucose L - glucose Naturally occurring enantiomer D isomer When the hydroxyl group on the reference carbon is on the right in a projection formula that has a carbonyl group on top, the sugar Most hexoses of living organisms are D isomers  Cyclic Structure – Haworth Structure Aldehydes and ketones react with alcohol in a 1:1 ratio to form hemiacetals or hemiketals, creating a new chiral center at the carbonyl carbon Unstable- contains an additional asymmeteric carbon atom A hemiacetal/ hemiketal contains a hydroxyl group (OH) and an alkoxy group (OR) on the same carbon.  Cyclic Structure – Haworth Structure Cyclic hemiacetals form readily when the hydroxyl and carbonyl groups are part of the same molecule. Stable  Cyclic Structure – Haworth Structure Cyclic hemiacetals/ hemiketals contain an addition asymmetric carbon atom and can exist in two stereoisomeric forms designated as α and β. α – indicates that the hydroxyl group at the anomeric center is in a Fisher projection, on the same side as the hydroxyl attached at the farthest chiral center β – indicates that these hydroxyl groups are on opposite sides ANOMERS- isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom ANOMERIC CARBON- the hemiacetal (carbonyl) carbon atom MUTAROTATION- when the α and β anomers of D- glucose interconvert in an aqueous solution Cyclic Structure – Haworth Structure 1 1 Anomeric carbon 1 1 1 Alpha Beta More stable form (α) (β) Anomers Cyclic Structure – Haworth Structure  Cyclic Structure – Haworth Structure β 1 1 α α-D-Glucose β-D-Glucose 1 1 α-D-Galactose β-D-Galactose  Cyclic Structure – Haworth Structure 1 Anomeric carbon OH 5 C=O 2 HOCH2 CH2OH HOCH2 OH 2 2 H HO HO H OH H H CH2OH OH H OH H α-D-fructose β-D-fructose  Cyclic Structure – Haworth Structure β 1 1 α α-D-Glucose β-D-Glucose Humans have α-amylase (an enzyme) and they can digest starch products such as pasta (contain α-glucose) Humans do not have β-amylase (an enzyme) and they cannot digest cellulose such as wood or paper (contain β-glucose)  Chair Conformation β-D-Glucose β-D-Glucose (Haworth projection) (Chair conformation)  Mutarotation Change in specific rotation that accompanies the equilibration of α and β anomers in aqueous solution. β-D-glucose Open-chain form α-D-glucose (acyclic) 64% < 0.02% 36%  Physical properties of Monosaccharides - Colorless - Sweet Tasting - Crystalline solids - Polar with high melting points (because of OH groups) - Soluble in water and insoluble in nonpolar solvents (H-bond because of OH groups) Chemical properties of Monosaccharides 1. Formation of Glycosides (Acetals) 2. Oxidation 3. Reduction  Formation of Glycosides (Acetals) - Exist almost exclusively in cyclic hemiacetal forms. - They react with an alcohol to give acetals. - Acetals are stable in water and bases but they are hydrolyzed in acids. β-D-Glucose Methyl β-D-Glucoside Methyl α-D-Glucoside  Oxidation of Monosaccharides O H Aldonic acids + 2Cu 2+ OH- + 2Cu+ Benedict’s (Brick red) Reagent (blue) D - glucose D – gluconic acid Reducing sugars: reduce another substance.  Oxidation of Monosaccharides Rearrangement (Tautomerism) D-fructose D-glucose (ketose) (aldose)  Oxidation of Monosaccharides primary alcohol at C-6 of a hexose is oxidized to uronic acid by an enzyme (catalyst). Enzyme D-glucuronic acid D-glucose (a uronic acid) Exist in connective tissue Detoxifies foreign phenols and alcohols Monitoring Glucose Levels Glucose oxidase O2 H2O2  Reduction of Monosaccharides Alditols Sugars alcohols: sweetners in many sugar-free (diet drinks & sugarless gum). Problem: diarrhea and cataract MONOSACCHARIDES SACCHARIDES GREEK word for SUGAR With ONE sugar molecule Cannot be further reduced by HYDROLYSIS Can be directly absorbed in the bloodstream from the small intestine  TYPES OF MONOSACCHARIDES ACCORDING TO THE LOCATION OF THE CARBONYL GROUP Some important Monosaccharides GLUCOSE  Glucose (Dextrose) (C6H12O6, aldohexose) – Blood sugar The most abundant monosaccharide Is found in fruits, vegetables, corn syrup, and honey. Is found in disaccharides such as sucrose, lactose, and maltose. Makes up polysaccharides such as starch, cellulose, and glycogen.  Glucose (Dextrose) - Normal blood glucose levels are 70-110 mg/dL. - Excess glucose is stored as the polysaccharide glycogen or as fat. - Insulin (a protein produced in the pancreas) regulates blood glucose levels by stimulating the uptake of glucose into tissues or the formation of glycogen. - Patients with diabetes produce insufficient insulin to adequately regulate blood sugar levels, so they must monitor their diet and/or inject insulin daily. Some important Monosaccharides Fructose (C6H12O6, ketohexose), Is the sweetest of the carbohydrates. Is found in fruit juices and honey (fruit sugar). In bloodstream, it is converted to its isomer, glucose. Is bonded to glucose in sucrose (a disaccharide known as table sugar). Some important Monosaccharides Galactose (C6H12O6, aldohexose), Has a similar structure to glucose except for the –OH on Carbon 4. Cannot find in the free form in nature. Exist in the cellular membranes of the brain and nervous system. Combines with glucose in lactose (a disaccharide and a sugar in milk). CARBOHYDRATE DISORDER Galactosemia missing the enzyme that convert galactose to glucose GALACTOSE-1-PHOSPHATE URIDYL TRANSFERASE Accumulation of galactose in the blood and tissues Mental retardation and cataract Solution: removing the galactose from food: no milk  DISACCHARIDES Consists of two monosaccharides linked by a glycosidic bond (when one –OH group reacts with another –OH group). Glucose + Glucose Maltose + H2O Glucose + Galactose Lactose + H2O Glucose + Fructose Sucrose + H2O  GLYCOSIDIC BOND a covalent bond that joins the hemiacetal group of a saccharide to the hydroxyl group of the other saccharide Methyl alc. CONDENSATION IN GLYCOSIDIC BONDING GLYCOSIDIC BOND GLYCOSIDIC BOND Some important Disaccharides MALTOS E Is a disaccharide of two glucose molecules. Has a α -1,4-glycosidic bond (between two α-glucoses). Is obtained from the breakdown of starches. Is used in cereals and candies. Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize). α -1,4-glycosidic bond β 1 + 4 1 4 + H 2O α-glucose α-glucose β- maltose Some important Disaccharides LACTOSE Is a disaccharide of galactose and glucose. Has a β -1,4-glycosidic bond (between β-galactose and α-gulcose). Is found in milk and milk products (almost no sweet). Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize). β β-lactose Some important Disaccharides SUCROSE Is found in table sugar (obtained from sugar cane and sugar beets). Consists of glucose and fructose. Has an α,β-1,2-glycosidic bond (between α-glucose and β-fructose). Is not a reducing sugar (carbon 1 cannot open to give a free aldehyde to oxidize). β-1,2-glycosidic bond  SUCROSE Sucrose is very sweet, but contains many calories. To reduce caloric intake, many artificial sweeteners have been developed. Aspartame, Saccharin, Sucralose These artificial sweeteners were discovered accidentally. Artificial sweeteners Aspartame: It (sold as Equal) is hydrolyzed into phenylalanine, which cannot be processed by those individuals with the condition phenylketonuria.  Artificial sweeteners Saccharine: It (sold at Sweet’n Low) was used extensively during World War I. There were concerns in the 1970s that saccharin causes cancer.  Artificial sweeteners Sucralose: It (sold as Splenda) has a very similar structure to sucrose.  OLIGOSACCHARIDES Verbascose Stachyose carbohydrates that contain between 3 and 10 single sugar residues not relatively abundant in the diet when compared to other more common carbohydrates like those in the disaccharide category. The raffinose family of oligosaccharides comprise: raffinose (trisaccharide) stachyose (tetrasaccharide) and verbascose (pentasaccharide) all occur in the seeds of legumes, as well as in different parts of plants  OLIGOSACCHARIDES Maltotriose is a metabolite found in or produced by Escherichia coli (strain K12, MG1655). Maltotriose is a trisaccharide (three-part sugar) consisting of three glucose molecules linked with α-1,4 glycosidic bonds.  POLYSACCHARIDES Polymers of many monosaccharides (starch that stores glucose in plants such units. as rice, potatoes, beans, and wheat - energy storage). Amylose (20%) Starch Amylopectin (80%) Glycogen (an energy storage in animals & humans) Cellulose (plant and wood structures). Some important Polysaccharides AMYLOSE Is a polysaccharide of α-glucose in a continuous (unbranched) chain (helical or coil form). Has α-1,4-glycosidic bonds between the α-glucose units (250 to 4000 units). Some important Polysaccharides AMYLOPECTIN Is a polysaccharide of glucose units in branched chains. Has α-1,4-glycosidic bonds between the α-glucose units. Has α-1,6 bonds to branches of glucose units. (at about every 25 glucose units, there is a branch). Both forms of starch are water soluble. Some important Polysaccharides GLYCOGE N highly branched-every 10-15 units). - It is similar to amylopectin (more - It is an energy storage molecule found in animals/humans. - It is stored mainly in the liver and in muscle cells. - When glucose is needed for energy, glucose units are hydrolyzed from the ends of the glycogen polymer. - is highly branched, there are many ends available for hydrolysis  Polysaccharides Amylose, Amylopectin (starch) H+ or α-amylase (enzyme in saliva) Dextrins (6-8 glucose units) Digestion process H+ or α-amylase (enzyme in pancreas) Maltose (2 glucose units) H+ or α-maltase (enzyme) Many α-D-glucose units  Respiration C6H12O6 + 6O2 6CO2 + 6H2O + energy glucose Some important Polysaccharides CELLULOSE Is a polysaccharide of glucose units in unbranched chains with β-1,4-glycosidic bonds (2200 glucose units). Has rigid structure (H-bond) and insoluble in water. Is the major structural material of wood & plants (cotton: 100%). Cannot be digested by humans because of the β-1,4-glycosidic bonds (needs an enzyme: β-glycosidase). Some important Polysaccharides CELLULOSE - Cellulose makes up the insoluble fiber in our diets. - It passes through the digestive system without being metabolized. - Fiber is important in adding bulk to waste to help eliminate it more easily (even though it gives us no nutrition).  Useful Carbohydrates Amino Sugars They contain an -NH2 group in place of an -OH group. - The most abundant amino sugar in nature is D-glucosamine. - Glucosamine helps keep the cartilage in joints healthy. But natural glucosamine levels drop as people age. - As a supplement, glucosamine is most often used to try to ease the joint pain caused by arthritis.  Useful Carbohydrates Amino Sugars - The second most abundant amino sugar in nature is Chitin. - It is a polysaccharide formed from N-acetyl-D-glucosamine units joined together by 1,4- β-glycosidic bonds. - Its structure is similar to cellulose (insoluble in water).  Useful Carbohydrates Glycosaminoglycans (GAGs) They are a group of unbranched carbohydrates derived from alternating amino sugar and glucuronate units. Hyaluronate: extracellular fluids that lubricate joints and in the vitreous humor of the eye. β-glycosidic bond  Useful Carbohydrates Glycosaminoglycans (GAGs) Chondroitin: a component of cartilage and tendons. β-glycosidic bond Heparin: stored in the mast cells of the liver, helps prevent blood clotting. α-glycosidic bond  Useful Carbohydrates Blood Type - There are four blood types—A, B, AB, and O. - Blood type is based on 3 or 4 monosaccharides attached to a membrane protein of red blood cells. - Each blood type has the monosaccharides below:  Useful Carbohydrates Blood Type Type A blood contains a fourth monosaccharide: Type B contains an additional D-galactose unit. Type AB has both type A and type B carbohydrates. Useful Carbohydrates Blood Type Useful Carbohydrates Blood Type  Useful Carbohydrates Blood Type - The short polysaccharide chains distinguish one type of the red blood cell from another, and signal the cells about the foreign viruses, bacteria, and other agents. - The blood of one individual may contain antibodies to another type. - Those with type O blood are called universal donors, because people with any other blood type have no antibodies to type O. - Those with type AB blood are universal recipients because their blood contains no antibodies to A, B, or O. Useful Carbohydrates Blood Type