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Chapter 6 Carbohydrates Outline 6.1 Classes of Carbohydrates 6.1

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Chapter 6 Carbohydrates Outline 6.1 Classes of Carbohydrates 6.1 2/25/2015 Outline Lecture Presentation • 6.1 Classes of Carbohydrates • 6.2 Functional Groups in Monosaccharides Chapter 6 • 6.3 Stereochemistry in Monosaccharides Carbohydrates • 6.4 Reactions of Monosaccharides • 6.5 Disaccharides • 6.6 Polysaccharides Julie Klare • 6.7 Carbohydrates and Blood Fortis College Smyrna, GA © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.1 Classes of Carbohydrates 6.1 Classes of Carbohydrates • The simplest carbohydrates are • Disaccharides consist of two monosaccharide monosaccharides (mono is Greek for “one,” units joined together. sakkhari is Greek for “sugar”). • A disaccharide can be split into two • These often sweet-tasting sugars cannot be monosaccharide units. Ordinary table sugar, broken down into smaller carbohydrates. sucrose, C12H22O11, is a disaccharide that can be broken up, through hydrolysis, into the • The common carbohydrate glucose, C6H12O6, is a monosaccharide. monosaccharides glucose and fructose. • Monosaccharides contain carbon, hydrogen, • Oligosaccharidesare carbohydrates and oxygen and have the general formula containing three to nine monosaccharide units. The blood-typing groups known as ABO are Cn(H2O)n, where n is a whole number 3 or higher. oligosaccharides. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.1 Classes of Carbohydrates 6.1 Classes of Carbohydrates • When 10 or more monosaccharide units are joined together, the large molecules that result are polysaccharides (poly is Greek for “many”). • The sugar units can be connected in one continuous chain or the chain can be branched. • Starch, a polysaccharide in plants, contains branched chains of glucose that can be broken down to produce energy. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 1 2/25/2015 6.1 Classes of Carbohydrates 6.1 Classes of Carbohydrates FIBER IN YOUR DIET FIBER IN YOUR DIET • Dietary fibers are carbohydrates that we cannot digest • Insoluble fibers do not mix with water, although they with our own enzymes. play a critical role in the digestive tract. • Soluble fiber mixes with water, forming a gel-like • Insoluble fiber has a laxative effect and adds bulk to the substance in the stomach and digestive tract. diet, thus preventing constipation. • This gives a sense of fullness and slows sugar and • The polysaccharide cellulose is an insoluble fiber. cholesterol absorption into the bloodstream. • Sources include whole grains, seeds, brown rice, • Some foods high in soluble fiber include oatmeal, cabbage, and vegetable skins. legumes (peas, beans, and lentils), apples, psyllium husk, and carrots. • Fruit pectins used in making jellies contain soluble fiber. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.2 Functional Groups in Monosaccharides 6.2 Functional Groups in Monosaccharides • Carbohydrates are • Alcohols are classified by the number of alkyl groups considered attached to the carbon atom bonded to the hydroxyl group. polyhydroxyaldehydes • A primary (1) alcohol has one alkyl group. or polyhydroxy ketones • A secondary (2) alcohol has two alkyl groups. because they contain • A tertiary (3) alcohol has three alkyl groups. several hydroxyl • Monosaccharides contain primary and secondary alcohols. (alcohol) groups and either an aldehyde or ketone group. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.2 Functional Groups in Monosaccharides 6.2 Functional Groups in Monosaccharides • Members of the aldehyde family always have a carbonyl group with • The ketone family of organic compounds is a hydrogen atom bonded to one side of the carbonyl and an alkyl or structurally similar to the aldehydes. aromatic group bonded to the other. • The difference is that ketones have an alkyl or • Monosaccharides can contain an aldehyde functional group at one end of the molecule (in addition to multiple hydroxyl groups). aromatic group on both sides of the carbonyl. • Ketones occur in a wide variety of biologically relevant compounds. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 2 2/25/2015 6.2 Functional Groups in Monosaccharides 6.3 Stereochemistry in Monosaccharides • A monosaccharide that contains an aldehyde functional • A carbon atom with tetrahedral geometry and four group is an aldose, and one that contains a ketone different atoms or groups attached to it is chiral. functional group is a ketose. • A compound with a single chiral carbon atom can • A monosaccharide with three carbons is a triose, one exist as two enantiomers. with four carbons is a tetrose, one with five carbons is • How many chiral carbons does a glucose molecule a pentose, and one with six carbons is a hexose. contain? – Carbon 1 is not tetrahedral, and carbon 6 does not have four different groups attached. – Carbons 2 to 5 are tetrahedral and have four different atoms or groups of atoms attached, so they are chiral carbons. • Glucose has a four chiral centers. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.3 Stereochemistry in Monosaccharides 6.3 Stereochemistry in Monosaccharides • The number of stereoisomers possible increases with the number of chiral centers present in a molecule. • The general formula for determining the number of stereoisomers is 2n, where n is the number of chiral centers present in the molecule. • Because glucose has four chiral centers, 16 stereoisomers are possible. • Only only one of these stereoisomers is our preferred energy source. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.3 Stereochemistry in Monosaccharides 6.3 Stereochemistry in Monosaccharides • In the Fischer projection, horizontal lines on a chiral center represent wedges, and vertical lines on a chiral center represent dashes. • A chiral carbon is not shown as a “C” on a Fischer projection but is implied at the intersection of the lines. • This gives the viewer a quick and easy way of identifying the number of chiral centers. • The designation of D or L is based on the Fischer projection positioning in glyceraldehyde, used as a reference molecule for this designation. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 3 2/25/2015 6.3 Stereochemistry in Monosaccharides 6.3 Stereochemistry in Monosaccharides • D-sugars have the –OH on the chiral carbon farthest from the • When we draw enantiomers in a Fischer projection, carbonyl C=O on the right side of the molecule. they are written as if there is a mirror placed between • The enantiomer is the L-sugar, which has the –OH group on the two molecules. the chiral carbon farthest from the C=O on the left side of the projection. • Attached atoms or groups on the right in one • Most of the carbohydrates found in nature and the ones we use enantiomer appear on the left side of the other. for energy are D-sugars. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.3 Stereochemistry in Monosaccharides 6.3 Stereochemistry in Monosaccharides Drawing an Enantiomer in a Fischer Projection Stereoisomers That Are Not Enantiomers • Step 1: Locate the chiral centers. • Stereoisomers that are not enantiomers are called • Step 2: Switch horizontal groups on the chiral centers. diastereomers. • Diastereomers are stereoisomers that are not exact mirror images. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.3 Stereochemistry in Monosaccharides 6.3 Stereochemistry in Monosaccharides Important Monosaccharides: Glucose Important Monosaccharides: Galactose • The most abundant monosaccharide found in nature is • Galactose is found combined with glucose in the glucose, also called dextrose, blood sugar, or grape disaccharide lactose, which is present in milk and other sugar. dairy products. • It is found in fruits, vegetables, and corn syrup. • Galactose has a single chiral center (carbon 4) arranged • Diabetics have difficulty getting glucose from the opposite that of glucose. bloodstream into their cells so that glycolysis can occur. • Diastereomers that differ in just one chiral center are This is why they must regularly monitor their blood epimers. glucose levels. • The body can convert galactose into glucose with an • Glucose is also a sugar unit in sucrose (table sugar), enzyme called an epimerase. lactose (milk sugar), amylase, amylopectin, glycogen, and cellulose. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 4 2/25/2015 6.3 Stereochemistry in Monosaccharides 6.3 Stereochemistry in Monosaccharides Important Monosaccharides: Mannose Important Monosaccharides: Fructose • Mannose is a monosaccharide • The ketose fructose is also found most notably in referred to as fruit sugar or cranberries. It is not easily levulose. It is found in fruits, absorbed by the body. vegetables, and honey. • In combination with glucose, • Mannose has been shown to be it gives us the disaccharide effective against urinary tract sucrose (table sugar). infections (UTIs). When the level • Fructose is the sweetest of mannose builds up in the monosaccharide, one and a half bladder, bacteria will attach times sweeter than table sugar. themselves to the mannose in • Even though it is not an epimer the urine and be eliminated. of glucose, fructose can be • Mannose is an epimer of broken down for energy glucose. production in the body. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.3 Stereochemistry in Monosaccharides 6.4 Reactions of Monosaccharides Important Monosaccharides: Ribose • Linear structures do not show how most • The pentoses (five-carbon sugars) monosaccharides actually are structured. ribose and 2-deoxyribose are a part
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