Chem 20: Ch. 13 Carbohydrates Study Guide

Haworth Structures of Fructose P. 15

FRUCTOSE -is a ketohexose -forms a five-atom ring structure with carbon 2 at the right corner of the ring. -forms when the -OH group on carbon 5 reacts w/ carbon 2 in the carbonyl group.

Stereoisomers

Stereoisomers have identical molecular formulas -and are not structural isomers -with atoms bonded in the same sequence but differ in the way they are arranged in space. When the mirror images of organic molecules cannot be completely matched, they are -NONSUPERIMPOSABLE -CHIRAL (pronunciation 'kai-rel)

13.5 Chemical Properties of Monosaccharides. P. 16

Sugar alcohols such as D-sorbitol, D-xylitol from D-xylose, and D-mannitol from D-mannose are used as sweeteners in many sugar free products such as diet drinks and sugarless gum as well as products for people with diabetes.

Sweetness of Sweeteners P. 22

Sugars and artificial sweeteners -differ in sweetness -are compared to sucrose (table sugar), which is assigned a value of 100.

Types of Carbohydrates p. 2

The types of carbohydrates are -MONOSACCHARIDES, the simplest carbohydrates -DISACCHARIDES, which consist of two monosaccharides. -POLYSACCHARIDES, which contain many monosaccharides.

Carbohydrates and Flatulence

-Beans ("the magical fruit") contain the trisaccharide RAFFINOSE. -Humans lack the enzyme necessary to hydrolyze this carbohydrate. -Intestinal bacteria consumes the raffinose in a manner similar to lactose, producing the familiar biological activity politely referred to as flatulence. -What exactly is Beano?

Glycosidic Linkages

-Each sugar unit in a polysaccharide is joined by a glycosidic linkage. -Which functional group best describes the glycosidic linkage? -The rings can bond with each other from the same face of the rings (bottom to bottom) or from opposite faces. -An ALPHA LINKAGE occurs when the bonding comes from the same face of the molecule. -The two bonds appear to be coming from beneath the rings. -A BETA LINKAGE involves bonding on the opposite faces -One bond appears to be becoming from beneath a ring, the other from above the ring.

Lactose Intolerance

-In normal adults, the disaccharide lactose is broken up into glucose and galactose by the enzyme LACTASE during digestion -Individuals who lack an adequate concentration of this enzyme are said to be LACTOSE INTOLERANT. -Instead of being broken up naturally by the body, bacteria in the digestive tract break up the lactose, producing gases in this process, which in turn causes discomfort.

Starch

-Starch occurs in two common forms -AMYLOSE consists of long, coiling helixes -AMYLOPECTIN also consists of helixes, with other helixes branching off from each other. -When starch is consumed, it is converted to GLYCOGEN, which has a branched structure similar to amylopectin.

Polysaccharides (continued) P. 26

-The individual saccharide units can often bond together in different patterns, producing polysaccharides with different properties. -The familiar complex carbohydrate STARCH contains glucose molecules joined together by an ⍺-linkage (alpha linkage) -Changing the orientation of one bond in the individual units gives the polysaccharide known as CELLULOSE, which is held together by ß-linkages (beta linkages) -Starch forms a twisted structure called a HELIX; cellulose instead forms long chains.

Carbohydrates in the Diet P. 29

-The primary role of carbohydrates in the diet is to provide an immediate energy source -The brain demands a significant amount of energy, using glucose as its fuel. -Any excess carbohydrates are generally converted by the body into fat. -Low-fat and non-fat foods can still cause you to gain weight as a result!

Making and Breaking the Bonds of Polysaccharides.

-When two individual sugar molecules come together to form a disaccharide, water is given off as a side product. -Recall that we call this type of reaction a CONDENSATION REACTION. -Similarly, water can be added to a disaccharide or polysaccharide to break the molecule into smaller sugar units. -We call this a HYDROLYSIS REACTION.

Disaccharides P. 20

A DISACCHARIDE -consists of two monosaccharides linked together -is formed when two monosaccharides combine in a dehydration reaction MONOSACCHARIDE DISACCHARIDE ___________________________________ ______________________________ glucose + glucose ------------> maltose + H2O glucose + galactose-----------> lactose + H2O glucose + fructose-------------> sucrose + H2O The most common disaccharides are maltose, lactose, and sucrose.

Drawing Fischer Projections

A FISCHER PROJECTION -is a two-dimensional representation of a 3-D molecule -places the most highly oxidized carbon group at the top -uses vertical lines in place of dashes for bonds that go back -uses horizontal lines in place of wedges for bonds that come forward.

Fischer Projections

A FISCHER PROJECTION used to represent carbohydrates -places the most oxidized group at the top -shows chiral carbons as the intersection of vertical and horizontal lines. -shows the -H and -OH groups on the horizontal intersecting line. -places the -CH2OH group at the bottom of the Fischer projection, which is not chiral.

Study Check: Identify each as aldo or keto and as tetrose, pentose, or hexose. P. 3

A. ALDOHEXOSE B. KETOPENTOSE

Learning Check: Identify the polysaccharides and types of glycosidic bonds in each of the following: P. 28 A. Picture of tree B. Picture of Potatoes

A. Cellulose ß-1,4-glycosidic bonds B. Amylose ⍺-1,4-glycosidic bonds Amylopectin ⍺-1,4- and ⍺-1,6-glycosidic bonds

Study Check: Identify the following Fischer projections of aldose as L or D isomers: P. 7

A. D-Isomer. -OH is on the right B. L-Isomer; -OH is on the left.

Study Check: Indicate whether each pair is a mirror image that cannot be superimposed (enantiomers). P. 6

A. YES B. NO

Amylopectin

AMYLOPECTIN -makes up as much as 80% of starch -is a branched-chain polysaccharide -contains glucose molecules connected by ⍺-1,4-and ⍺-1,6-glycosidic bonds Starches hydrolyze easily in water and acid to give smaller saccharides, called DEXTRINS, which then hydrolyze to maltose and finally glucose.

Polysaccharide: Amylopectin P. 27

AMYLOPECTIN, found in plants, -is a polymer of ⍺-D-glucose molecules. -is a branched-chain polysaccharide -has ⍺-1,4-glycosidic bonds between the glucose units -has ⍺-1,6 bonds to branches.

Amylose

AMYLOSE -makes up about 20% of starch -consists of 250 to 4000 ⍺-D-glucose molecules connected by ⍺-1,4-glycosidic bonds in a continuous chain. -is called a straight-chain polymer even though the polymers of amylose are actually coiled in helical fashion.

Polysaccharide: Amylose P. 27

AMYLOSE is -makes up about 20% of starch -consists of 250 to 4000 ⍺-D-glucose molecules connected by ⍺-1,4-glycosidic bonds in a continuous chain -is called a straight-chain polymer even though the polymers of amylose are actually coiled in helical fashion.

Artificial Sweeteners: Aspartame P. 23

ASPARTAME is -marketed as NutraSweet or Equal -a noncarbohydrate sweetener made form aspartic acid and a methyl ester of the amino acid phenylalanine.

13.1 Carbohydrates P. 1

CARBOHYDRATES are -a major source of energy from our diet -made from the elements carbon, hydrogen, and oxygen -also called saccharides, which means "sugars". Carbohydrates, such as glucose, -are produced by photosynthesis in plants. -are synthesized in plants from CO2, H2O, and energy from the sun. -are oxidized in living cells to produce CO2, H2O, and energy

Cellulose

CELLULOSE, the major structural unit of wood, -is a polysaccharide of glucose units in unbranched chains with ß-1,4-glycosidic bonds -cannot form hydrogen bonds with water; thus, it is insoluble in water -gives a rigid structure to the cell walls in wood and fiber -is more resistant to hydrolysis than are the starches -cannot be digested by humans b/c humans cannot break down ß-1,4-glycosidic bonds.

Cellulose P. 28

CELLULOSE< the major structural unit of wood, is the most abundant organic chemical on Earth. -is a polysaccharide of glucose units in unbranched chains -has ß-1,4-glycosidic bonds -cannot be digested by humans b/c humans cannot break down ß-1,4-glycosidic bonds -None the less, it is useful as digestive tract. Other polysaccharides can be found throughout nature which provide support to cells, acting as "small-scale skeletons"

Chirality

CHIRAL MOLECULES have -the same number of atoms but are arranged differently in space -a nonsuperimposable mirror image. Hands are like chiral molecules-they are mirror images and cannot be superimposed. When the mirror images of molecules are identical and superimposable, the molecules are ACHIRAL.

Chitin P. 26

CHITIN is the polysaccharide which makes up the hard exoskeletons of insects and some crustaceans -the monosaccharide units that make up chitin are called N-acetylglucosamine; note that this saccharide contains nitrogen.

D and L Notations P. 6

D or L isomers are assigned according to the position of the -OH group on the chiral carbon farthest from the carbonyl carbon. -The letter L is assigned to the structure with the -OH on the left. -The letter D is assigned to the structure with the -OH on the right.

Galactose P. 12

D-GALACTOSE -is an aldohexose, C6H12O6 -is not found free in nature -is obtained from the disaccharide lactose -has a similar structure to glucose except for the -OH on carbon 4. In a condition called galactosemia, an enzyme needed to convert galactose to glucose is missing.

Glucose and Fructose P. 11

D-GLUCOSE is -found in fruits, corn syrup, and honey -an aldohexose with the formula C6H12O6 -known as dextrose and blood sugar in the body -a building block in sucrose, lactose, maltose, and in polysaccharides such as cellulose and glycogen. D-FRUCTOSE, obtained from sucrose is -a ketohexose with the formula C6H12O6 -the sweetest of the carbohydrates, twice as sweet as sucrose. The sweet taste of honey comes from the monosaccharides D-glucose and D-fructose.

Monosaccharides P. 11

D-Galactose has the same structure as D-Glucose, except that the -OH group on C-4 is switched (right on D-Glucose and left on D-Galactose).

Monosaccharides (continued) P. 12

D-Glucose and D-Fructose are the same on carbons 3, 4, 5, and 6. The only differences occur at C-1 and C-2.

Oxidation: Fructose to Glucose P. 17

FRUCTOSE, a ketohexose, -contains a ketone group, which usually can't be oxidized -can be oxidized in a basic Benedict's solution when a rearrangement occurs between the ketone group on carbon 2 and the hydroxyl group on carbon 1. -is then converted to glucose, which produces an aldehyde group with an adjacent hydroxyl that can be oxidized. Fructose, a ketohexose, rearranges to form glucose and is then oxidized in Benedict's.

Glycogen

GLYCOGEN is -a polymer of glucose that is stored in the liver and muscle of animals -hydrolyzed in our cells at a rate that maintains the blood level of glucose and provides energy between meals. -similar to amylopectin, but it is more highly branched. The glucose units in glycogen are joined by ⍺-1,4-glycosidic bonds, with branches attached by ⍺-1,6-glycosidic bonds that occur every 10-15 glucose units.

Glycogen

GLYCOGEN, or ANIMAL STARCH, -is the polysaccharide that stores ⍺-D-glucose in muscle -is similar to amylopectin, but is more highly branched -the glucose units are joined by ⍺-1,4-glycosidic bonds, and branches occurring about every 10-15 glucose units are attached by ⍺-1,6-glycosidic bonds.

13.3 Fischer Projections of Monosaccharides p. 8

Glucose, galactose, and fructose are the most important monosaccharides.

D and L Notations

In a Fischer projection, the -OH group on the -chiral carbon FARTHEST FROM THE CARBONYL GROUP determines an L or D isomer. -left is assigned the letter L -right is assigned the letter D

Lactose, Milk Sugar P. 21

LACTOSE -is a disaccharide found in milk and milk products -makes up 6-8% of human milk and about 4- 5% of cow's milk.

Lactose P. 21

LACTOSE is a disaccharide of ß-D-galactose and ⍺-or ß-D-glucose. The bond in lactose is a ß-1,4-glycosidic bond because the -OH group on carbon 1 of ß-D-galactose forms a glycosidic bond with the -OH group on carbon 4 of a D-glucose molecule.

13.6 Disaccharides P. 19

Lactose is a disaccharide found in milk and milk products. It contains the monosaccharides galactose and glucose.

13.2 Chiral Molecules P. 3

Left and right hands are chiral because they have mirror images that cannot be superimposed on each other.

Maltose

MALTOSE is -a disaccharide also known as MALT SUGAR -composed of two D-glucose molecules -obtained from the hydrolysis of starch -used in cereals, candies, and brewing -found in both the ⍺ and ß forms.

Monosaccharides P. 2

MONOSACCHARIDES -consist of three to eight carbon chains with one carbon in a carbonyl group -containing an aldehyde group are classified as an ALDOSES -containing a ketone group are classified as a KETOSES -have hydroxyl groups on all carbons except the carbonyl carbon.

Formation of Maltose P. 21

Maltose is linked by an alpha-1,4-glycosidic bond formed from the ⍺-OH on carbon 1 of the first glucose and -OH on carbon 4 of the second glucose.

Chiral Carbon Atoms P. 5

Molecules are chiral when they have -at least one or more CHIRAL CARBON atoms -a carbon atom, bonded to four different groups -nonsuperimposable mirror images -The MIRROR IMAGE of a chiral compound cannot be superimposed. -When stereoisomers cannot be superimposed, they are called ENANTIOMERS.

Structural Isomers P. 3

Molecules are structural isomers when they have the same molecular formula but different bonding arrangements.

Types of Monosaccharides P. 2

Monosaccharides are also classified by the number of carbon atoms present. TRIOSE (three C atoms) TETROSE (4 C atoms) PENTOSE (5 C atoms) HEXOSE (6 C atoms) An ALDOPENTOSE is a five carbon saccharide with an aldehyde group. A KETOHEXOSE is a six carbon saccharide with a ketone group.

Oxidation of Monosaccharides P. 17

Monosaccharides in solution -have small amounts of the open-chain form present -have an aldehyde group with an adjacent hydroxyl group that can be oxidized to carboxylic acid by an oxidizing agent such as Benedict's. Sugar acids -are produced from the oxidation of the aldehyde form as Cu2+ is reduced to Cu+ -are named by replacing the OSE ending of the monosaccharide with ONIC ACID. A carbohydrate that reduces another substance (such as the open chain form of D-glucose) is called a REDUCING SUGAR.

Polysaccharides P. 26

POLYSACCHARIDES -are formed when monosaccharides are joined together and contain hundreds to thousands of individual units -They perform numerous roles in living structures -Most Polysaccharides are polymers of D-glucose include amylose and amylopectin, starches made of ⍺-D-glucose. -Include glycogen (animal starch in muscle), which is made of ⍺-D-glucose -include cellulose (plants and wood), which is made of ß-D-glucose.

Study Check: In the following Fischer projection of mannose, identify the monosaccharides as a D or an L isomer. P. 9

SOLUTION:

Study Check: In the following Fischer projection, A. identify the number of chiral centers. B. identify the monosaccharide as a D or an L isomer. P. 10

SOLUTION:

Study Check: Write the product for the reduction of D-mannose. P. 18

SOLUTION:

Study Check: Write the cyclic forms of D-galactose P. 15

SOLUTION: STEP 1: Turn Fischer projection clockwise by 90º STEP 2: Fold clockwise to make a hexagon and bond O on carbon 5 to carbonyl group. -Place carbon 6 group above ring. -Write the -OH group on carbon 2 below the ring and the -OH groups on carbon 3 and carbon 4 above the ring. STEP 3: Draw the new -OH group on carbon 1 below the ring to give the alpha isomer or above the ring to give the ß isomer:

Study Check: Identify the monosaccharides in each of the following: P. 23 A. lactose B. Maltose C. sucrose

SOLUTION: A. lactose (1) ⍺-D-glucose (3) ß-D-galactose B. Maltose (1) ⍺-D-glucose C. sucrose (1) ⍺-D-glucose (2) ß-D-fructose

Study Check: Melibiose is a disaccharide that is 30 times sweeter than sucrose. P. 25 A. What are the monosaccharide units in melibiose? B. What type of glycosidic bond links the monosaccharides? C. Identify the structure as ⍺- or ß-melibiose

SOLUTION: A. ⍺-D-galactose and ⍺-D-glucose B. ⍺-1,6-glycosidic bond C. ⍺-melibiose

Guide for Drawing Hayworth Structures

STEP 1: Turn the Fischer projection clockwise by 90º. STEP 2: Fold the horizontal carbon chain into a hexagon and bond the O on carbon 5 to the carbonyl group. STEP 3: Draw the new -OH group on carbon 1 below the ring to give the alpha isomer or above the ring to give the ß isomer.

Cyclic Structure for Glucose P. 14-15

STEP 1: turn Fischer projection clockwise by 90º STEP 2: Fold clockwise to make hexagon and bond the O on carbon 5 to carbon 1. -Place the carbon 6 group in the -CH2OH group above carbon 5 -Draw a bond between the oxygen of the -OH group on carbon 5 to the carbonyl carbon. STEP 3: Draw the new -OH group on carbon 1 below the ring to give the alpha isomer or above the ring to give the ß isomer.

Artificial Sweeteners: Sucralose P. 23

SUCRALOSE is -marketed as Splenda -made from sucrose by replacing some of the hydroxyl groups with chlorine atoms.

Sucrose, Table Sugar P. 22

SUCROSE, or TABLE SUGAR, -is obtained from sugar cane and sugar beets -consists of ⍺-D-glucose and ß-D-fructose -has an ⍺,ß-1,2-glycosidic bond between carbon 1 of glucose and carbon 2 of fructose. -cannot form an open chain and cannot be oxidized -cannot react with Benedict's reagent and is not a reducing sugar.

13.7 Polysaccharides P. 26

The polysaccharide cellulose is composed of glucose units connected by ß-1,4-glycosidic bonds.

Reduction of Monosaccharides P. 18

The reduction of the carbonyl group in monosaccharides -produces sugar alcohols, which are also called ALDITOLS -converts D-glucose to the sugar alcohol D-sorbitol.

Reducing Sugars P. 18

The sugar alcohols -are named by replacing the ose ending of the monosaccharide with itol. -include D-sorbitol, D-xylitol from D-xylose, and D-mannitol from D-mannose -are used as sweeteners in many sugar-free products such as diet drinks and sugarless gum.

Monosaccharides P. 12

To draw D-Ribose, think of D-Glucose but leave out C-3 and the attached -OH and -H groups.

Mutarotation alpha- and ß-D-Glucose P. 15

When placed in solution, -cyclic structures open and close -alpha-D-glucose converts to ß-D-glucose and vice versa -at any time, only a small amount of open chain forms.

Achiral Carbon Atoms P. 5

When the mirror image of an achiral structure is rotated, and the structures can be aligned with each other, their mirror images are said to be superimposable.

Monosaccharides P. 11

You must know the structure of these four monosaccharides. begin by learning the structure of D-Glucose: the pattern of -OH group is right, left, right, right