Chem 150 Unit 9 - Biological Molecules II Carbohydrates
Chem 150 Unit 9 - Biological Molecules II Carbohydrates Carbohydrates play many important roles in biological systems. They represent the major form of chemical energy for both plants and animals. In plants they represent the end product of photosynthesis, and therefore connect all living systems to the suns sustaining light energy. Our discussion of carbohydrates will also introduce us to biopolymers, of which proteins and nucleic acids also belong. One of these polymers, the structural polysaccharide cellulose, ties more of the earths organic carbon than any other molecule. Introduction Polymers are large molecules that are made by stringing together, like beads on a string, smaller units called monomers. Poly- is the Greek prefix meaning many. The names of may polymers describe what they are made from Polyethylene is made by stringing together many ethylene units.
Ethylene (ethene) is the monomer Polypropylene is made by stringing together many propylene units. Propylene (propene) is the monomer. Polysaccharides are made by stringing together many monosaccharides. Monosaccharides (simple sugars) are the monomers. 22 Introduction Carbohydrates are placed in to one of three catagories, depending on the number of monosaccharide units, or residues, they contain. Monosaccharides, contain a single monosaccharide residue. Oligosaccharides, contain 2 to 10 monosaccharide residues. These include the disaccharides, which contain 2 monosaccharide residues.
Polysaccharides, which contain more than 10 monosaccharide residues. These can contain thousands of monosaccharide residues. 33 Monosaccharides Monosaccharides are polyhydroxy aldehydes or ketones. Monosaccharides contain 3 to 7 carbon atoms. 44 Monosaccharides Monosaccharides are classified according to the number of carbons and whether they contain an aldehyde or ketone.
The -ose ending is used to designate carbohydrates. 55 Question (Clickers) The monosaccharide shown below is a member of which type of monosaccharide? A) Aldotetrose B) Aldopentose C) Ketopentose D)
Aldohexose E) 66 Ketohexose CH2 OH C O HO C OH H
C OH H C OH CH2 OH Question (Clickers) The monosaccharide shown below is a member of which type of monosaccharide? A) Aldotetrose O B) C)
Ketopentose D) Aldohexose E) 77 Aldopentose Ketohexose H C H C
OH HO C OH H C OH CH2 OH Monosaccharides The physical properties of monosaccharides are heavily influenced by the large number of hydroxy groups that they contain. There ability to participate in
numerous hydrogen bonds gives them high melting points and high solubilities in water. Each hydroxyl group has two 88 hydrogen bonding acceptor sites and one hydogen bonding donor site. Each carbonyl group has two acceptor sites. O H H O H
O H H H O C H C O H H H
H O H O H Monosaccharides Monosaccharides contain chiral carbon atoms. This is what accounts for the large number of different monosacchides. For each chiral carbon, n, a monosacharide has 2n stereoisomers. These will be divided among 2n/2 pairs of enantiomers. Glucose contains 4 chiral carbons Glucose has 24 = 16 stereoisomers These stereoisomers can be grouped into 16/2 = 8 pairs of enantiomers.
O H C H C OH HO C OH H C OH
H C OH H C OH H D-glucose http://www.preparatorychemistry.com/Bishop_Jmol_carbohydrates.htm 99 Monosaccharides Fischer projections are used to distinguish the
different stereoisomers. The letters D and L are used to distinguish between the members of a pair of enantiomers. The D or L designation is based on the chiral carbon furthest from the carbonyl carbon. 11 00 Fischer projection: Question (Clickers) How many stereoisomers does the the monosaccharide shown below have? A) 5
B) 32 C) 16 D) 8 E) 11 11 3 CH2 OH C
O HO C OH H C OH H C OH CH2 OH
Question (Clickers) Is the monosaccharide shown below a D- or and L- isomer? A) D-isomer B) L-isomer CH2 OH C O HO C OH
H C OH HO C H CH2 OH 11 22 Monosaccharides Diasteriomers are stereoisomers that are not enantiomers. Diasteriomers have have different names Enatiomers have the same name and are distinguished by a D or L.
enantiomers diastereomers 11 33 Monosaccharides Important monosaccharides. pentose and hexoses are the most abundant Pentoses D-ribose and D-2-deoxyribose are found in DNA, RNA and nucleotides such as FADH2 and NADH 11 44 Monosaccharides Important monosaccharides. pentose and hexoses are the most abundant Hexoses D-glucose (dextrose or blood surgar) major metabolite and strorage form of
chemical energy. D-galactose - combines with glucose to produce lactose (milk sugar) D-fructose (fruit sugar) - major metabolite and sweetest tasting natural sugar. fructose is a ketose 11 55 Monosaccharides Monosaccharide derivatives Deoxy sugars. One or more -OHs are replaced with -Hs 11 66 Monosaccharides Monosaccharide derivatives Amino sugars. One or more -OHs are replaced with -NH2s
Often these are acetylated to form amides. Arthritis relief?? 11 77 Monosaccharides Monosaccharide derivatives Alcohol sugars. The ketone or aldehyde is reduced to an alcohol are reduced to 11 88 Monosaccharides Monosaccharide derivatives Carboxylic acid sugars. The ketone, aldehyde, or primary alcohol is oxidized to a carboxylic acid. 11
99 Question The monosaccharide D-xylose is shown below. Draw the derivative describe: A) B) C) 22 00 D-2-deoxyxylose xylitol D-xylonic acids (carbon 1 is oxidized to a carboxylic acid) O H C
H C OH HO C H H C OH CH2 D-xylose
OH Reactions in Cookies!! http://www.food-info.net/uk/colour/maillard.htm http://patft.uspto.gov/netacgi/nph-Parser ?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u= %2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50 &s1=5091200.PN.&OS=PN/5091200&RS=PN/5091200 But beware acrylamide in fries!! 22 11 Reactions of Monosaccharides Reduction of the carbonyl In the lab this can be done with H2 and a platinum catalyst. In the cell, NADH + H+ is used. 22
22 Reduction of Aldehydes and Ketones (Unit 8) The same reaction can also be used to reduce aldehydes and ketones to alcohols: 22 33 Reduction of Aldehydes and Ketones (Unit 8) In biochemistry, NADH + H+ is used instead of H2 The reduction of a ketone containing steroid by the enzyme Hydroxsteroid dehydrogenase. 22 44 Reactions of Monosaccharides Oxidation of sugars Oxidation with Cu+ The Benedicts test Sugars that are capable of producing a positve Benedicts test are called reducing sugars.
22 55 Oxidation of Aldehydes (Unit 8) Aldehydes can also be oxidized with the copper(II) ion (Cu2+) This reaction oxidizes aldehydes, but not alcohols. The Cu2+ ion forms a clear blue solution The Cu+ that is produced in the reaction forms an orange/red precipitate. 22 66 Oxidation of Aldehydes (Unit 8) Aldehydes can also be oxidized with the copper(II) ion (Cu2+) The reaction is called the Benedicts reaction, and has been used for years
in a clinical setting to test O H for the presence of C glucoseH inC the urine. OH HO C H H C OH H
C OH CH2 OH glucose Cu2+ 22 77 Cu2+ + Cu+ Cu+ Reactions of Monosaccharides Oxidation of sugars Even though ketones should not give a positive Benedicts test, ketoses do. This is because under the basic conditions of the test, the ketoses can isomerize to form aldoses, which the react.
22 88 Reactions of Monosaccharides Reactions with alcohols to form hemiacetals and hemiketals Since monosaccharides contain both hydroxyl groups along with either aldehyde or ketone groups, they can react to form hemiacetals and hemiketals. 22 99 Reactions of Alcohols with Aldehydes and Ketones (Unit 7) The first reaction, which is similar to the reduction of aldehydes and ketones, involves adding an alcohol across the carbonyl to form a hemiacetal (from aldehydes) or a hemiketal (from ketones). O H3C
CH2 C Propanal (Aldehyde) H + O CH2 CH3 Ethanol (Alcohol) O H + O CH2 CH3
33 00 CH2 C O CH2 CH3 (Hemiacetal) O H CH3 C O CH3
CH3 Propanone (Ketone) H H H CH3 C H3C O Ethanol (Alcohol) (Hemiketal) CH2 CH3
Reactions of Alcohols with Aldehydes and Ketones (Unit 7) Hemiacetal and hemiketal formation is catalyzed by acids. 33 11 Reactions of Alcohols with Aldehydes and Ketones (Unit 7) As we will see with the carbohydrates, the carbonyl group and the alchohol that react can come from the same molecule. This will produce a ring molecule. 33 22 Cyclic Form of Monosaccharides Monosaccharides form rings by reacting one of the hydroxyls with the carbonyl to form a hemiacetal or hemiketal:
http://www.preparatorychemistry.com/Bishop_Jmol_carbohydrates.htm 33 33 Cyclic Form of Monosaccharides Usually these are drawn using a Haworth project: The OHs that were on the right in the Fisher projection are placed in the down position on the Haworth projection The OHs that were on the left in the Fisher projection are placed in the up position on the Haworth projection The CH2OH on the number 5 carbon points up for D sugars and down for L sugars. 33 44 Cyclic Form of Monosaccharides The hemiacetal or hemiketal carbon that forms in the ring is called the anomeric carbon.
The anomeric carbon is also chiral, which increases the number of chiral carbons by 1 and increases the doubles the number of stereoisomers. The two forms of the anomeric carbon are designated as or . The -anomer has the -OH pointing up in the ring form. The -anomer has the -OH pointing down in the ring form. 33 55 Cyclic Form of Monosaccharides The ring formation is a dynamic equilibrium reaction. The open form can switch back and forth between the two ring forms. 33 66 Cyclic Form of Monosaccharides When naming the ring forms of monosaccharides, the endings -pyranose and -furanose to designate the sixmember and five-member rings, respectively.
33 77 Cyclic Form of Monosaccharides In general, the -OH on the chiral carbon furthest from the the carbonyl is the one that reacts to from the pyranose or furanose ring. This means that Aldohexoses will form pyranose rings: D-glucose (aldohexose) Aldopentoses and ketohexoses will form furanose rings: D-ribose (aldopentose) D-fructose (ketohexose) 33
88 Question (Clicker) Shown to the below is the Fischer projection forCH sorbose 2 OH C O H C OH HO C H
H C OH CH2 OH Is the structure shown A) D-sorbose B) L-sorbose Draw and name the and ring forms for sorbose 33 99 CH2OH OH
O CH3OH H H OH H OH -D-sorbofuranose CH2OH OH O OH H
H H OH CH2OH -D-sorbofuranose Question (Clicker) Shown to the below is the Fischer projection forO galactose H H C HO C H
H C OH H C OH HO C H CH2 OH Is the structure shown
A) D-galactose B) L-galactose H O CH2OH OH H OH OH OH 44 00 H
-L-galactopyranose H H O OH CH2OH OH H H OH OH Draw and name the and ring forms for sorbose H
H -L-galactopyranose Oligosaccharides Monosaccharides are connected to one another to form oligosaccharides and polysaccharides by reacting the anomeric (hemiacetal or hemiketal) hydroxyl group on one sugar in its ring form, with a hydroxyl group from another sugar. We saw in Unit 8 how this leads to the formation of acetals and ketals. The bond that forms between the two monosaccharides is called a glycosidic bond. 44 11 Reactions of Alcohols with Aldehydes and Ketones (Unit 7) A hemiacetal or hemiketal can react with a second alcohol to form an acetal or ketal.
This is a substitution reaction and produces an water molecule: O H3C CH2 C H + O H H + O H O CH2 CH3 CH2 CH3
44 22 CH2 CH3 CH2 C O Ethanol (Alcohol) CH2 CH3 + H O H H
O H H (Acetal) O CH3 C CH2 CH3 O CH3 CH3 (Hemiketal) O H3C Ethanol
(Alcohol) (Hemiacetal) CH3 C CH2 CH3 CH2 CH3 H O O (Ketal) CH2 CH3 + Oligosaccharides The disaccharide D-maltose forms when the anomeric
carbon on a D-glucopyranose molecule in the form reacts with the hydroxyl group on the forth carbon of a second Dglucopyranose molecule: The bond that forms is called an (14) glycosidic bond Maltose is produced from the breakdown of the polysaccharides starch and glycogen 44 33 Oligosaccharides Maltose is still able to reduce Cu+ in a Benedicts test, though it is only 1/2 as reactive. Like monosaccharides, maltose is considered a reducing sugar. This is because the one monosaccharide is still
able to open to expose an aldehyde. nonreducing end 44 44 reducing end Oligosaccharides The disaccharide D-cellobiose forms when the anomeric carbon on a D-glucopyranose molecule in the form reacts with the hydroxyl group on the forth carbon of a second Dglucopyranose molecule: The bond that forms is called an (14) glycosidic bond Cellobiose is produced from the breakdown of the polysaccharids cellulose. 44 55
Unlike the (14) glycosidic bond in maltose, most organisms are unable to cleave the (14) glycosidic bond Oligosaccharides The disaccharide D-lactose forms when the anomeric carbon on a D-galactopyranose molecule in the form reacts with the hydroxyl group on the forth carbon of a Dglucopyranose molecule: The bond that forms is called an (14) glycosidic bond Lactose is milk sugar. By the age of 5, some people become unable to break the (14) glycosidic bond in lactose, resulting in lactose intolerance.
44 66 Oligosaccharides The disaccharide D-sucrose forms when the anomeric carbon on a D-glucopyranose molecule in the form reacts with the hydroxyl group of the anomeric carbon of Dfructofuranose in the form: The bond that forms is called an ,(12) glycosidic bond Sucrose is table sugar. Because both anomeric carbons are involved in forming the glycosidic bond, sucrose is not a reducing sugar. 44 77 Oligosaccharides
There are also oligosaccharides with 3 or more monosaccharides The blood group antigens are oligosaccharides that are attached to lipids and proteins found on cell surfaces. A: N-Acetyl-D-galactosamine (as shown) B: D-galactose O: none 44 88 Polysaccharides Polysaccharides are polymers of 10 or more monosaccharide units Homopolysaccharides contain a single type of monosaccharide unit. Heteropolysaccharides contain more than one typee of monosaccharide unit. 44
99 Polysaccharides The polysaccharide cellulose is a structural polymer produced by plants: It is a linear, unbranched polyer, with D-glucopyranose units connected by (14) glycosidic bonds 55 00 Polysaccharides The polysaccharide cellulose is a structural polymer produced by plants: Cellulose forms a very insoluble, fibrous network Most organism are unable to digest cellulose because they lac the enzymes needed to break the (14) glycosidic bonds 55 11
Polysaccharides The polysaccharide starch is a polymer produced by plants for glucose storage: It is a linear, or branched polymer, with D-glucopyranose units connected by (14) glycosidic bonds amylose amylopectin 55 22 Polysaccharides The polysaccharide starch is a polymer produced by plants for glucose storage: Unlike cellulose, starch has a very open and soluble structure. Animals also produce a storage form of glucose called glycogen, which has a structure similar to amylopectin. 55 33
Polysaccharides Heteropolymers Hyaluronic acid Found in lubricating fluid that surrounds joints and in the vitreous humor of the eye. 55 44 Polysaccharides Heteropolymers Chondroitin Sulfate Present in connective tissue 55 55 The End
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