Carbohydrates • Basic formula (CH2O)n • Don’t worry about L and D isomers, He won’t ask about them on the test
Carbohydrates • Two important things that we need to know about every sugar • 1. Number of Carbons • 4 Carbons= Tetroses, 5 Carbons=Pentoses, 6 Carbons=Hexoses • 2. Aldose or Ketose? Ketone Aldehyde Glucose Fructose
Carbohydrates • A good way to figure out how many total isomers that are possible for a sugar is to figure out the number of chirality centers and take 2numberofchiralitycenters . • How might you figure out the number of chirality centers, you might ask? • Take the number of carbons, now subtract 2 if it is an aldose and 3 if the sugar is a ketose. • Example: fructose is a ketose with 6 carbons, 6-3=3, so fructose has 3 chirality centers and 23 isomers, or 8.
Carbohydrates • When carbohydrates cyclize, the –OH group on the number 5 carbon binds with whichever carbon has the carbonyl group. • In aldoses that is the number 1 carbon and in ketoses the number 2 carbon. • The former carbonyl carbon now becomes an anomeric carbon, because it is connected to 2 oxygen atoms.
Carbohydrates • You can tell if a ring structure is an aldose or ketose by finding the anomeric carbon and seeing what it is bound to. If it is an aldose, then it will be bound to 2 oxygens, 1 carbon, and 1 hydrogen. A ketose’s anomeric carbon will be bound to 2 carbons and 2 oxygens. 2 Oxygens 2 Oxygens 2 Carbons Anomeric Carbon Anomeric Carbon 1Carbon, 1hydrogen
Carbohydrates • Sugars with free aldehyde or anomeric carbons are called reducing sugars. • “Free” means not participating in a bond, or glycosidic linkage. • The anomeric carbon’s -OH group can be in up or down position, if it is up this is “beta” and if it is down it’s called “alpha”. • We use the α and β designations to describe the sugar and the bonds that an anomeric carbon’s –OH group may participate in.
Glycosidic linkages • It is very important to be able to name glycosidic linkages, the covalent bonds between sugars. • They are named by the carbons that are bound together. • If the anomeric carbon is involved, then we have to include the α or β designation of that carbon when naming the bond.
Glycosidic Linkages • Let’s practice: What’s the bond? α1-4
Glysodic Linkages • Glycosidic linkages combine simple sugars into larger molecules • 2 sugars (or monosaccharides) make up a disaccharide • 3 or more make up an oligosaccharide • Several sugars make up a polysaccharide • A large molecule made up of the same sugar is called a polymer
Monosaccharides • You need to know glucose’s structure as well as fructose, galactose, and ribose. • The easiest way is to memorize glucose and then know how it differs from the others • For example. Glucose and galactose look exactly the same except for the –OH group on the number 4 carbon is opposite, fructose is a five member ring with 6 carbons and ribose is a five member ring with only five carbons.
Disaccharides • You’ll need to know the following disaccharides: • 1. Maltose • 2.Sucrose • 3. Lactose • Know the monosaccharides that are in each and the type of glycosidic linkage in each. • Those things are how a disaccharide is distinguished from other disaccharides. • These characteristics are on the next slide (test yourself)
Disaccharides • Maltose- 2 Glucoses in an α1-4 glycosidic linkage • Sucrose- a Glucose and Fructose in an α1-β2 linkage • Lactose- a Galactose and Glucose in a β1-4 linkage
Glucose Polymers • Finally, know the three glucose polymers: • 1. Starch • 2.Glycogen • 3.Cellulose • Like the disaccharides, you’ll want to know the glycosidic linkages in each polymer.
Glucose Polymers • Starch has α1-4 and α1-6 linkages • Glycogen has α1-4 and α1-6 linkages, but twice as many α1-6 linkages as starch, or more branches • Cellulose has β1-4 linkages, and is also known as dietary fiber
Glycemic Index • Usually a question is asked on Glycemic index • The question always wants to know the parts of the graph • Basically know that the graph’s axis are plasma concentration of glucose vs. time and that the area under the curve represents glycemic index.