Presentation on theme: "XXXI. Carbohydrates A.Overview Carbohydrates are the most abundant class of naturally occurring organic compounds. They make up 50% of the earth’s biomass."— Presentation transcript:
XXXI. Carbohydrates A.Overview Carbohydrates are the most abundant class of naturally occurring organic compounds. They make up 50% of the earth’s biomass and are found in animals, plants, fungi and bacteria. 1.The first carbohydrates had molecular formulas similar to hydrates C n (H 2 O) n 2.D-Glucose is the most abundant carbohydrate found in nature.
3. Biological Systems CO 2 + H 2 O + Energy (Photosynthesis) Starch Glucose Cellulose Animals Humans Plants Glycogen Glucose H 2 O + CO 2 + Energy
B. Classification Carbohydrates Simple Complex Monosaccharides Disaccharides (can not be hydrolyzed Oligosaccharides to simpler sugars) Polysaccharides Starch Glycogen Cellulose
C. D and L Configurations D & L designations are based on the configuration about the single stereocenter in glyceraldehyde. 2.Tetroses Erythrose and Threose Right Left (R)-2,3-Dihydroxypropanal 1. Trioses
3. Hexoses 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. D and L sugars are enantiomers of one another.
D. Epimers Carbohydrates that differ in configuration at only one carbon center. => Not Epimers
E. Cyclic Hemiacetals of Monosacchaarides 2. Glucose 1. Cyclic Hemiacetal - Mechanism
3. Anomers Carbohydrates that differ in configuration only at their anomeric carbon. An anomeric carbon is a hemiacetal or acetal carbon in a carbohydrate.
E. Cyclic Hemiacetals of Monosacchaarides β-D-Glucopyranoseα-D-Glucopyranose β-D-Glucoseα-D-Glucose 2. Glucose 4. Chair 1. Cyclic Hemiacetal - Mechanism
5. Cyclic Structure for Fructose β-D-Fructofuranose
F. Mutarotation 1. When anomers dissolved in water undergo a slow change in optical rotation to an equilibrium value, this process is called mutrotation. 2. Only sugars with hemiacetal anomeric carbons can undergo mutarotation. 3. Sugars which undergo mutarotation are called reducing sugars.
4. Mutarotation of Glucose 64%36%0.2% β-D-Glucopyranoseα-D-Glucopyranose
H. Disaccharides A Disaccharide on hydrolysis is cleaved to two monosaccharides. The monosaccharides are linked as a glycoside (acetal).
1. Cellobiose Two glucose units linked β-1-4’. Disaccharide of cellulose. A mutarotating, reducing sugar. =>
2. Maltose Two glucose units linked α-1-4’. Disaccharide of starch A mutarotating, reducing sugar =>
3. Amylopectin Branched, insoluble fraction of starch, α-1-4’, α-1-6’ every 20-30 glucose units. =>
4. Cellulose Polymer of β-D-glucose, found in plants. Mammals lack the -glycosidase enzyme. Rigid linear structure. =>
5. Glycogen Glucose polymer, α-1-4’, α-1-6’ every 10 glucose units. Similar to amylopectin, but even more highly branched. Energy storage in muscle tissue and liver. The many branched ends provide a quick means of putting glucose into the blood. =>
Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin. But glycogen has more a(1 6) branches. The highly branched structure permits rapid release of glucose from glycogen stores, e.g., in muscle during exercise. The ability to rapidly mobilize glucose is more essential to animals than to plants.
Gentiobiose Two glucose units linked 1-6’. Rare for disaccharides, but commonly seen as branch point in carbohydrates. =>