Carbohydrates linco larry

Carbohydrates Scheffler LincoLarry Jln High School 2008 Version 1.10 Carbohydrates • Contain Carbon, Hydrogen and Oxygen • Can be characterized as – Monosaccharides – Disaccharides – Polysaccharides • Includes sugars, starches, cellulose, Carbohydrates Produced by plants during photosynthesis; contains C, H, O Monosaccharides Single (simple) sugars; quick energy Contain C, H, and O in 1:2:1 ratio Examples: Glucose C6H12O6 Fructose C6H12O6 Galactose C6H12O6 glucose fructose Types of Carbohydrates Carbohydrates have the following basic composition: I (CH2O)n or H - C - OH I  Monosaccharides - simple sugars with multiple OH groups Based on number of carbons (3, 4, 5, 6), a monosaccharide is a triose, tetrose, pentose or hexose  Disaccharides - monosaccharides covalently linked  Oligosaccharides - a few monosaccharides covalently linked  Polysaccharides - polymers consisting of chains of monosaccharide or disaccharide units Monosaccharides • Empirical formula is CH2O • Open chain and ring structures are possible • Many structural isomers are possible • The most common forms have: – Five carbons C5H10O5 - called pentoses – Six carbons C6H12O6 - called hexoses • Contain at least one carbonyl group C=O • If the carbonyl group is at the end it is an aldose sugar • If it is within the chain it is a ketose sugar • Multiple chiral carbon atoms lead to optical isomers • Usually have between and carbon atoms Monosaccharides Aldoses (e.g., glucose) have an aldehyde group at one end H C Ketoses (e.g., fructose) have a ketone group, usually at C2 O CH2OH C O HO C H OH H C OH OH H C OH H C OH HO C H H C H C CH2OH CH2OH D-glucose D-fructose Optical Isomers: D and L D or dextrorotatory & L or levorotatory are designations for optical isomers that are based on the configuration about the single asymmetric C in glyceraldehyde The lower representations are Fischer Projections CHO CHO H C OH HO L-glyceraldehyde CHO H C OH CH2OH D-glyceraldehyde H CH2OH CH2OH D-glyceraldehyde C CHO HO C H CH2OH L-glyceraldehyde Sugar Nomenclature For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group Most naturally occurring sugars are D isomers O H C H – C – OH HO – C – H H – C – OH H – C – OH CH2OH D-glucose O H C HO – C – H H – C – OH HO – C – H HO – C – H CH2OH L-glucose Steroisomers D & L sugars are mirror images of one another They have the same name, e.g., D-glucose & L-glucose Other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc O H C H – C – OH HO – C – H H – C – OH H – C – OH CH2OH D-glucose O H C HO – C – H H – C – OH HO – C – H HO – C – H CH2OH L-glucose The number of stereoisomers is 2n, where n is the number of asymmetric centers The 6-C aldoses have asymmetric centers Thus there are 16 stereoisomers (8 D-sugars and Lsugars) Ring Structures Pentoses and hexoses can form ring structures as the ketone or aldehyde reacts with a distal OH Glucose forms an intra-molecular hemiacetal, as the C1 aldehyde & C5 OH react, to form a 6-member ring known as a pyranose ring, H HO H H CHO C OH C H C OH (linear form) C OH D-glucose CH2OH CH2OH CH2OH H OH H OH H O H H OH α-D-glucose OH H OH H OH H O OH H H OH β-D-glucose These representations of the cyclic sugars are called Haworth projections Fructose Ring Structures Fructose may form either  a 6-member pyranose ring, by reaction of the C2 keto group with the OH on C6, or  a 5-member furanose ring, by reaction of the C2 keto group with the OH on C5 Monosaccharides Some examples of pyranose ring structures for hexose sugars The ring is not actually planar but exists in boat and chair conformers Sugar Derivatives CH2OH CH2OH H O H OH H H OH OH H H NH2 α-D-glucosamine O H OH H H O OH OH H N C CH3 H α-D-N-acetylglucosamine An Amino sugar is a sugar in which an amino group substitutes for a hydroxyl An example is glucosamine The amino group may be converted to an amide, as in N-acetylglucosamine Anomers of Glucose CH2OH CH2OH H OH H OH H O H H OH α-D-glucose OH H OH H OH H O OH H H OH β-D-glucose Cyclization of glucose produces a new asymmetric center at C1 The stereoisomers are called anomers, α & β Haworth projections represent the cyclic sugars as having essentially planar rings, with the OH at the anomeric C1:  α (OH below the ring)  β (OH above the ring) Glycosidic Bonds The anomeric hydroxyl groups of two sugars can join together, splitting out water to form a glycosidic bond Two gluocose molecules combine to form a disaccharide known as maltose Disaccharides •Double sugars •Good source of energy •Break down into simple sugars Sucrose (glucose + fructose) Other disaccharides include: Lactose (glucose + galactose) Sucrose, common table sugar, has a glycosidic bond linking the anomeric hydroxyls of glucose & fructose Because the configuration at the anomeric C of glucose is α (O points down from ring), the linkage is α(1→2) The full name of sucrose is α-D-glucopyranosyl-(1→2)-β− D-fructopyranose.) Lactose, milk sugar, is composed of galactose & glucose, H H with β(1→4) linkage from the anomeric OH of galactose Its full name is β-D-galactopyranosyl-(1→ 4)-α-Dglucopyranose Disaccharides •Compare the structures of these three common disaccharides H H •Sucrose is an A (1-4) link between D-Glucose and DFructose •Lactose is Polysaccharides •3 or more sugars linked together •Storage energy •Complex sugars Examples: Starch- (plants) found in leaves, tubers… Glycogen- (animals) found in the liver and muscles Cellulose- (plants) make up cell walls Starch Cellulose • Major building component of plant cell walls • Long chain of glucose molecules; should be great source of energy, but… • Humans cannot digest cellulose since they lack the necessary enzyme • Endosymbiotic protist in cow guts DOES have the enzyme Polysaccharides _Starches CH2OH O H H OH H OH H OH H H O 6CH OH O H OH H H H H O CH2OH CH2OH CH2OH O H OH H H OH H H O O H OH H OH H OH H H O O H OH H H OH H OH amylose • Plants store glucose as amylose or amylopectin Both are glucose polymers collectively called starch • Glucose storage in polymer form minimizes osmotic effects  Amylose is a glucose polymer with α (1→4) linkages  The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end Polysaccharides _Starches CH2OH H O H OH H OH H OH H H O 6CH OH O H OH H H H H O CH2OH CH2OH CH2OH O H OH H H OH H H O O H OH H OH H OH H H O O H OH H H OH H amylose • The Real difference between amylose starch and cellulose is in the glycosidic link between successive saccharide units OH Amylopectin CH2OH CH2OH O H H OH H H OH H O OH CH2OH H H OH H O H OH H H OH CH2OH O H OH H OH H H O O H OH H H OH H H O amylopectin H O CH2 H OH H CH2OH O H OH H H O CH2OH O H OH H H OH H H O O H OH H H OH H OH  Amylopectin is a glucose polymer with mainly α(1→4) linkages, but it also has branches formed by α (1→6) linkages Branches are generally longer than shown above • The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur Glycogen CH2OH CH2OH O H H OH H H OH H O OH CH2OH H H OH H O H OH H H OH CH2OH O H OH H OH H H O O H OH H H OH H H O glycogen H O CH2 H OH H CH2OH O H OH H H O CH2OH O H OH H H OH H H O O H OH H H OH H OH • Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin found in plants • Glycogern has more α (1→6) branches • The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise •T he ability to rapidly mobilize glucose is more essential to animals than to plants The End .. .Carbohydrates • Contain Carbon, Hydrogen and Oxygen • Can be characterized as – Monosaccharides – Disaccharides – Polysaccharides • Includes sugars, starches, cellulose, Carbohydrates. .. ratio Examples: Glucose C6H12O6 Fructose C6H12O6 Galactose C6H12O6 glucose fructose Types of Carbohydrates Carbohydrates have the following basic composition: I (CH2O)n or H - C - OH I  Monosaccharides