Chapter 23
Carbohydrates and Nucleic Acids

23-01

Labeled

Title
Structures of Glucose and Fructose
Caption
Figure 23-1 Glucose and fructose are monosaccharides. Glucose is an aldose (a sugar with an andehyde group), and fructose is a ketonse (a sugar with a ketone group).
Notes
Carbohydrate structures are commonly drawn usinf the Fischer projections.
Keywords
glucose, fructose, carbohydrates, Fischer projection
23-01-02UN

Labeled

Title
Classicfication of Monosaccharides
Caption
Sugars with aldehyde groups are called aldoses, and those with ketone groups are called ketoses. The number of carbon atoms in the sugar generally ranges from three to seven, designated by the term triose (three carbons), tetrose (four carbons), pentose (five carbons), hexose (six carbons), and heptose (seven carbons).
Notes
Most ketones have the ketone on C2, the second carbon of the chain.
Keywords
aldoses, ketoses, aldohexose, ketohexose, aldotetrose, ketotetrose, triose, tetrose, pentose, hexose, heptose
23-01-03UN

Labeled

Title
D and L Series of Sugars
Caption
The (+) enantiomer of glyceraldehyde has its OH group on the right of the Fischer projection. Therefore sugars of the D series have the OH groups on the bottom asymmetric carbon on the right of the Fischer projection; sugars of the L series have the OH of the bottom asymmetric carbon on the left.
Notes
D and L are enantiomers (mirror images).
Keywords
asymmetric carbon
23-02

Labeled

Title
Degradation of an Aldose
Caption
Figure 23-2 Degradation of an aldose removes the aldehyde carbon atom to give a smaller sugar.
Notes
Sugars of the D series give (+)-glyceraldehyde in degradation to the triose.
Keywords
degradation, aldose, glyceraldehyde, triose
23-03

Labeled

Title
The D Family of Aldoses
Caption
Figure 23-3 The D family of aldoses. All these sugars occur naturally except for threose, lyxose, allose, and gulose.
Notes
The family tree of D aldoses can be created by starting with D-(+)-glyceraldehyde and adding carbons one by one.
Keywords
threose, lyxose, allose, gulose, aldoses
23-03-01UN

Labeled

Title
Erytho and Threo Diastereomers
Caption
A diastereomer is called erythro if its Fischer projection shows similar groups on the same side of the molecule. It is called threo if similar groups are on opposite sides of the Fischer projection.
Notes
Hydroxylation of trans-crotonic acid produces two threo enantiomers, while hydroxylation of cis-crotonic acid produces two erythro enantiomers. Th erythro and threo forms are diastereomers.
Keywords
erythro, threo, crotonic acid, hydroxylation
23-04

Labeled

Title
Dissymetric Molecules
Caption
Figure 23-4 The term erythro and threo are used with disymmetric molecules whose ends are different.
Notes
The terms meso and (+), (-), or (d),(l) are preferred with symmetric molecules.
Keywords
erythro, threo, meso, disymmetric
23-04-01UN

Labeled

Title
Epimers
Caption
Sugars that differ only by the stereochemistry at a single carbon are called epimers, and the carbon atom they generally differ if generally stated.
Notes
If the number of a carbon is not specified, it is assumed to be C2.
Keywords
epimers
23-04-02UN

Labeled

Title
Mechanism of Cyclic Hemiacetal Formation
Caption
If the aldehyde group and the hydroxyl group are part of the same molecule, a cyclic hemiacetal results.
Notes
Cyclic hemiacetals are particularly stable if they result in five- or six-membered rings.
Keywords
hemiacetals
23-05

Labeled

Title
Glucose Conformations
Caption
Figure 23-5 Glucose exists almost entirely as its cyclic hemiacetal form.
Notes
The Haworth projection is widely used to draw the hemiacetals, although it may give the impression of the ring being flat. The chair conformation is more accurate.
Keywords
glucose, Haworth projection, chair conformation
23-06

Labeled

Title
Fructose
Caption
Figure 23-6 Fructose form a five-membered cyclic hemiacetal. Five-membered rings are usually represented as flat Haworth structures.
Notes
Since five-membered rings are not puckered as much as six-membered rings, they are usually depicted as flat Haworth projections.
Keywords
fructose, Haworth projection
23-07

Labeled

Title
Anomers of Glucose
Caption
Figure 23-7 The anomers of glucose. the hydroxyl group on the anomeric (hemiacetal) carbon is down (axial) in the a anomer and up (equatorial) in the b anomer. The b anomer of glucose has all its subtituents in equatorial positions.
Notes
The hemiacetal carbon is called the anomeric carbon, easily identified as the only carbon atom bonded to two oxygens.
Keywords
anomer, hemiacetal, anomeric carbon, equatorial position, axial position
23-08

Labeled

Title
Anomers of Fructose
Caption
Figure 23-8 The a anomer of fructose has the anomeric -OH group down, trans to the terminal -CH2OH group. The b anomer has the anomeric -OH group up, cis to the terminal -CH2OH.
Notes
Keywords
fructose, anomer, anomeric carbon
23-09

Labeled

Title
Mutarotation
Caption
Figure 23-9 An aqueous solution of D-glucose contains an equilibrium mixture of a-D-glucopyranose, b-D-glycopyranose, and the intermediate open-chain form, Cystallization below 98oC gives the a anomer, and cystallization above 98oC gives the b anomer.
Notes
Mutarotation occurs because the two anomers interconvert in solution.
Keywords
mutarotation, interconversion, glucopyranose
23-10

Labeled

Title
Base-Catalyzed Epimerization of Glucose
Caption
Figure 23-10 Under basic conditions, stereochemistry is lost at the carbon atom next to the carbonyl group.
Notes
The enolate intermediate is not chiral so reprotonation can produce either stereomer. Because a mixture of epimers results, this stereochemical change is called epimerization.
Keywords
epimer, epimerization, stereochemistry
23-11

Labeled

Title
Base-Catalyzed Enediol Rearrangement
Caption
Figure 23-11 Under basic condictions, the carbonyl group can isomerize to other carbon atoms. Aldoses equilibrate with ketoses via enediol intermediates.
Notes
Under strongly basic conditions, the combination of enediol rearragements and epimerization leads to a complex mixture of sugars.
Keywords
enediol rearragement, epimerization
23-11-03UN

Labeled

Title
Oxiation of Aldoses Using Bromine Water
Caption
Bromine water oxidizes the aldehyde group of an aldose to a carboxylic acid. Bromine water is used for this oxidation because it does not oxidize the alcohol groups of the sugar and it does not oxidize ketoses.
Notes
The reaction can be used as a qualitative method to identify aldoses.
Keywords
bromine, aldose, ketose
23-11-04UN

Labeled

Title
Nitric Acid Oxidation
Caption
Nitric acid is a stronger oxidizing agent than bromine water, oxidizing both the aldehyde group and the terminal -CH2OH group of an aldose to a carboxylic acid.
Notes
Treatment of aldose with nitric acid produces aldaric acid. Glucose is oxidized to glucaric acid.
Keywords
nitric acid, aldose, aldaric acid, glucaric acid
23-11-06UN

Labeled

Title
Tollens Test
Caption
In its open form, an aldose has an aldehyde group, which reacts with Tollens reagent to give an aldonic acid and a silver mirror. Sugars that reduce Tollens reagent to give a silver miror are called reducing sugars.
Notes
Tollens test is used as a qualitative test for the identification of aldehydes.
Keywords
Tollens test, silver mirror, reducing sugars
23-12

Labeled

Title
Nonreducing Sugars
Caption
Figure 23-12 Sugars that are full acetals are stable to Tollens reagent and are nonreducing. Such sugars are called glycosides.
Notes
Nonreducing sugars (glycosides) are acetals, and they do not mutarotate.
Keywords
nonreducing sugar, mutarotate
23-13

Labeled

Title
Aglycones
Caption
Figure 23-13 The group bonded the anomeric carbon o a glycoside is called an aglycone.
Notes
Some aglycones are bonded through an oxygen atom (a true acetal), and others are bonded through other atoms such as nitrogen.
Keywords
aglycones
23-14

Labeled

Title
Ether Formation
Caption
Figure 23-14 Treatment of an aldose or a ketose with methyl iodide and silver oxide gives the totally methylated ether.
Notes
If the conditions are carefully controlled, the stereochemistry at the anomeric carbon is usually preserved.
Keywords
aldose, methyl iodide, silver oxide, anomeric carbon
23-15

Labeled

Title
Ester Formation
Caption
Figure 23-15 Acetic anhydride and pyridine convert all the hydroxyl groups on a sugar to acetate esters. The stereochemistry at the anomeric carbon is usually preserved.
Notes
Sugar esters are readily crystallized and purified, and they dissolve in common organic solvents.
Keywords
acetate ester
23-15-02UN

Labeled

Title
Osazone Formation
Caption
Two molecules of phenylhydrazine condense with each molecule of the sugar to give an osazone, in which both C1 and C2 have been converted to phenylhydrazones.
Notes
Most osazones are easily crystallized, with sharp melting points. Melting points of osazone derivatives provide valuable clues for the identification and comparison of sugars.
Keywords
osazones, phenylhydrazine, phenylhydrazone
23-15-03UN

Labeled

Title
Ruff Degradation
Caption
The Ruff degradation is a two-step process that begins with bromine water oxidation of the aldose to its aldonic acid. Treatment of the aldonic acid with hydrogen peroxide and ferric sulfate oxidizes the carboxyl group to CO2 and gives an aldose with one less carbon atom.
Notes
The Ruff degradation is used mainly for structure determination and synthesis of new sugars.
Keywords
Ruff degradation, oxidation, hydrogen peroxide, ferric sulfate, aldose
23-15-04UN

Labeled

Title
Kiliani-Fischer Synthesis
Caption
The Kiliani-Fischer synthesis lengthens an aldose carbon chain by adding one carbon atom to the aldehyde end of the aldose.
Notes
This synthesis is useful both for determining the structure of existing sugars and for synthesizing new sugars.
Keywords
Kiliani-Fischer synthesis
23-15-26UN

Labeled

Title
Periodic Acid Cleavage of Carbohydrates
Caption
Because ether and acetal groups are not affected, periodic acid cleavage of a glycoside can help to determine the size of the ring.
Notes
Cleavage of methyl b-D-glucopyranoside produces 4 different products, implying an original six-membered ring.
Keywords
periodic acid, cleavage, diol
23-16

Labeled

Title
Disaccharides
Caption
Figure 23-16 A sugar reacts with an alcohol to give an acetal called glycoside. When the alcohol is part of another sugar, the product is a disaccharide.
Notes
A disaccharide is a sugar composed of two monosaccharide units.
Keywords
glycoside, disaccharide
23-16-01UN

Labeled

Title
b-Glucosidic Linkage
Caption
In cellobiose, the anomeric carbon of one glucose unit is linked through an equatorial (b) carbon-oxygen bond to C4 of another glucose unit.
Notes
The monosaccharides are joined together by the equatorial position of C1 and the equatorial position of C4'.
Keywords
b-1,4-glucosidic linkage, cellobiose
23-16-02UN

Labeled

Title
a Glucosidic Linkage
Caption
Like cellobiose, maltose contains a 1,4' glucosidic linkage between the two glucose units. The difference in maltose is that the stereochemistry of the glucosidic linkages is a rather than b.
Notes
The monosaccharides are joined together by the axial position of C1 and the equatorial position of C4'.
Keywords
glucosidic linkage, maltose
23-16-05UN

Labeled

Title
Linkage of Two Anomeric Carbons: Sucrose
Caption
Some sugars are joined by a direct glycosidic linkage between their anomeric carbon atoms: a 1,1' linkage.
Notes
Sucrose is composed of one glucose unit and one fructose unit by an oxygen atom linking their anomeric carbon atoms.
Keywords
sucrose, glucose, fructose, anomeric carbon
23-17

Labeled

Title
Cellulose
Caption
Figure 23-17 Cellulose is a b-1,4' polymer of D-glucose, systematically named poly(1,4'-O-b-D-glucopyranoside).
Notes
Cellulose is the most abundant organic material. Cellulose is synthesized by plants as a structural material to support the weight of the plant.
Keywords
cellulose
23-18

Labeled

Title
Amylose
Caption
Figure 23-18 Amylose is an a-1,4' polymer of glucose, systematically named poly(1,4'-O-a-D-glucopyranoside).
Notes
Amylose differs from cellulose only in the stereochemistry of the glycosidic linkage.
Keywords
amylose, cellulose
23-19

Labeled

Title
Amylose Helix
Caption
Figure 23-19 The amylose helix forms a blue charge-transfer complex with molecular iodine.
Notes
This is the basis of the starch-iodide test for oxidizers.
Keywords
amylose, starch-iodide complex
23-20

Labeled

Title
Amylopectin
Caption
Figure 23-20 Amylopectin is a branched a-1,6' polymer of glucose. At the branch points, there is a single a-1,6' linkage that provides the attachment point for another chain.
Notes
Glycogen has a similar structure, except that its branching is more extensive.
Keywords
amylopecting, a-1,6' linkage, glycogen
23-21

Labeled

Title
RNA Polymer
Caption
Figure 23-21 A short segment of the RNA polymer. Nucleic acids are assembled on a backbone made up of ribofuranoside units linked by phosphate esters.
Notes
DNA and RNA each contain four monomers, called nucleotides that differ in the structure of the bases bonded to the ribose units.
Keywords
RNA, nucleosides, ribofuranoside
23-22

Labeled

Title
Cytidine, Uridine, Adenosine, and Guanosine
Caption
Figure 23-22 The four common ribonucleosides are cytidine, uridine, adenosine, and guanosine.
Notes
Ribonucleosides are components of RNA based on glycosides of the furanose form of D-ribose.
Keywords
cytidine, uridine, adenosine, guanosine, ribonucleosides
23-23

Labeled

Title
Common Ribonucleotides
Caption
Figure 23-23 Four common ribonucleotides. These are ribonucleosides esterified by phosphoric acid at their 5'-position, the -CH2OH at the end of the ribose chain.
Notes
Ribonucleosides are joined together by phosphate esters linkages.
Keywords
ribonucleotides, ribonucleosides, phosphorilation
23-24

Labeled

Title
Phosphate Linkages
Caption
Figure 23-24 Two nucleotides are joined by a phosphate linkage between the 5'-phosphate group of one and the 3'-hydroxyl group of the other.
Notes
A molecule of RNA always has two ends (unless it is in the form of a large ring); one end has a free 3' group, and the other end has a free 5' group.
Keywords
phosphate linkage
23-24-03UN1-4

Labeled

Title
Common Deoxyribonucleosides
Caption
Four common deoxyribonucleosides that make up DNA.
Notes
The structure of the DNA polymer is similar to that of RNA, except there are no hydroxyl groups on the 2' carbon atoms of the ribose rings.
Keywords
deoxyribonucleosides
23-25

Labeled

Title
Base Pairing in DNA and RNA
Caption
Figure 23-25 Base pairing in DNA and RNA. Each purine forms a stable hydrogen-bonded pair with a specific pyrimidine base.
Notes
Guanine hydrogen bonds to cytosine in three place; adenine hydrogen bonds to thymine in two places.
Keywords
purine, pyrimidine, guanine, cytosine, adenine, thymine
23-26-01UN

Labeled

Title
Strands of DNA
Caption
Figure 23-26 DNA usually consists of two complimentary strands, with all the base pairs hydrogen-bonded together.
Notes
The two strands are anti-parallel, running in opposite directions. One strand is arranged 3' to 5', while the other runs in the opposite direction, 5' to 3' from left to right.
Keywords
complimentary strands
23-27

Labeled

Title
Double Helix
Caption
Figure 23-27 Double helix of DNA. Two complimentary strands are joined by hydrogen bonds between the base pairs.
Notes
This double strand coils into a helical arrangement.
Keywords
double helix
23-28

Labeled

Title
Replication
Caption
Figure 23-28 Replication of the double strand of DNA. A new strand is assembled on each of the original strands, with the DNA polymerase enzyme forming the phosphate ester bonds of the backbone.
Notes
A similar process transcribes DNA into a complimentary molecule of messenger RNA for use by ribosomes as template for protein synthesis.
Keywords
replication, DNA polymerase enzyme, ribosomes

© 1995-2002 by Prentice-Hall, Inc.
A Pearson Company
Distance Learning at Prentice Hall
Legal Notice