Carbohydrates Carbohydrate: a ________________ or ______________, or a substance that gives these compounds on hydrolysis Monosaccharide: a carbohydrate.

Carbohydrates

• Carbohydrate: a ________________ or ______________ , or a substance that gives these compounds on hydrolysis

• Monosaccharide: a carbohydrate that cannot be _____________ to a simpler carbohydrate– they have the general formula CnH2nOn, where n varies

from 3 to 8– aldose: a monosaccharide containing an aldehyde

group– ketose: a monosaccharide containing a ketone group

Fig 19.UN, p.472

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Monosaccharides• There are only two trioses

– often aldo- and keto- are omitted and these compounds are referred to simply as trioses; although this designation does not tell the nature of the carbonyl group, it at least tells the number of carbons

Dihydroxyacetone (a ketotriose)

Glyceraldehyde (an aldotriose)

CHO

CHOH

CH2OH

CH2OH

C=O

CH2OH

Monosaccharides• Glyceraldehyde contains a stereocenter and

exists as a pair of enantiomers

(S)-Glyceraldehyde(R)-Glyceraldehyde

CHO

C

CHO

CH OH

CH2OH CH2OH

HHO

Fig. 19.1, p.467

Fischer Projections• Fischer projection: a two dimensional

representation for showing the configuration of tetrahedral __________________ – ____________ lines represent bonds projecting

forward – vertical lines represent bonds projecting to the

______

(R)-Glyceraldehyde

CHO

CH OH

CH2OH

(R)-Glyceraldehyde

convert to a Fischer projection

H OH

CHO

CH2OH

D,L Monosaccharides

• In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde

(L)-Glyceraldehyde(D)-Glyceraldehyde

CHO

C

CHO

CH OH

CH2OH CH2OH

HHO

[]25 = +13.5°D

[]25 = -13.5°D

D,L Monosaccharides

• According to the conventions proposed by Fischer– D-monosaccharide: a monosaccharide that,

when written as a Fischer projection, has the -OH on its ___________ carbon on the right

– L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the ______

• Following are the two most common D-aldotetroses and D-aldopentoses

D,L Monosaccharides

D-ErythroseD-Threose D-Ribose 2-Deoxy-D- ribose

CH2OH

CHO

OH

CH2OH

CHO

OH

CH2OH

CHO

OHOH

OH

HH

H

HHO

H

CH2OH

CHO

HOH

OH

HH

H

OHH

H

D,L Monosaccharides• and the three common D-aldohexoses.

Note that one of these is an amino sugar

D-GlucosamineD-Glucose D-Galactose

CH2OH

CHO

OH

OHH

OH

H

HHO

H

CH2OH

OH

OH

HOH

H

CH2OH

CHO

OH

HH

OH

H

HOHO

H

CHO

NH2H

H

Table 19.1, p.468

Table 19.2, p.469

Cyclic Structure

• Monosaccharides have hydroxyl and carbonyl groups in the same molecule and exist almost entirely as five- and six-membered cyclic ______________ – __________ carbon: the new stereocenter

resulting from cyclic hemiacetal formation– _______ : carbohydrates that differ in

configuation at their anomeric carbons

Fig 19.UN, p.471

Fig 19.2, p.472

Haworth Projections

• Haworth projections– five- and six-membered hemiacetals are represented as

planar ________ or ________ , as the case may be, viewed through the edge

– most commonly written with the ________ carbon on the right and the hemiacetal oxygen to the back right

– the designation means that -OH on the anomeric carbon is cis to the terminal -CH2OH; ___ means that it is trans

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Mutarotation

• Mutarotation: the change in specific rotation that occurs when an or form of a carbohydrate is converted to an equilibrium mixture of the two

•Mutarotation: the change in specific rotation that occurs when an a or b form of a carbohydrate is converted to an equilibrium mixture of the two

D-Glucose

CH2OH

CHO

OHOHHOH

HH

HOH

-D-Glucopyranose (-D-Glucose)

C

H OH

HHO

HOH

H

CH2OHOH

OH()

H OH

HHO

HH

OH

H

CH2OHO

O

H

H

H OH

HHO

HOH()

OH

H

CH2OHO

-D-Glucopyranose (-D-Glucose)

+

anomeric carbon

5

5 5

5

44

4

(-D-Galactose)(-D-Galactose) -D-Galactopyranose

-D-Galactopyranose

D-Galactose

()

()

CH

OH

HO

HO

CH2OH

OOH

OHOH

HO

HO

OCH2OH

OCH2OH

HO

HO

OHOH

[]25 = +52.8°D

[]25 = +150.7°D

Reduction to Alditols• The carbonyl group of a monosaccharide

can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2/M

Ni+

D-Glucitol (D-Sorbitol)

D-GlucoseCH2OH

CH2OH

OH

OHH

OH

CH2OH

CHO

OH

OHH

OH

H

HHO

H

H

HHO

H

H2

Oxidation to Aldonic Acids

Precipitates as a silver mirror

+

O O

RCH Ag(NH3)2+ RCO

- NH4

+Ag

Tollens' solution

NH3, H2O+

citrate or tartrate buffer

Precipitates as a brick-red solid

++

O ORCH Cu

2+RCO

-Cu2O

• Oxidation of the -CHO group of an aldose to a -CO2H group can also be carried out using Tollens’, Benedict’s, or Fehling’s solutions

Oxidation to Aldonic Acids

• 2-Ketoses are also oxidized by these reagents because, under the conditions of the oxidation, 2-ketoses equilibrate with isomeric _________

An aldoseAn enediolA 2-ketose

CH2OH

C=O

CH2OH

C-OH

CH2OH

CHOH

CHOH

CH2OH

CHO

(CHOH)n (CHOH)n (CHOH)n

Fig 19.UNc, p.478

Glucose Assay

• The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid– this need stems from the high incidence of

diabetes in the population

Glucose Assay

• The glucose oxidase method is completely specific for D-glucose

+

+

glucose oxidase

D-Gluconic acid

Hydrogen peroxide

-D-Glucopyranose

OHOH

HOHO

CH2OHO

CH2OH

CO2H

OH

OHH

OH

H

HHO

H

H2O2

O2 + H2O

Glucose Assay

– the enzyme glucose oxidase is specific for -D-glucose

– molecular oxygen, O2, used in this reaction is reduced to hydrogen peroxide H2O2

– the concentration of H2O2 is determined experimentally, and is proportional to the concentration of glucose in the sample

– in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometricallyperoxidase +colored product +o-toluidine H2O2 H2O

Fig 19.UNa, p.480

Problem 19.40, p.491

Glycosides

• _________ bond: the bond from the anomeric carbon of the glycoside to an -OR group

• __________ are named by listing the name of the alkyl or aryl group attached to oxygen followed by the name of the carbohydrate with the ending -e replaced by -ide– methyl -D-glucopyranoside– methyl -D-ribofuranoside

Formation of Glycosides• Glycoside: a carbohydrate in which the -

OH of the anomeric carbon is replaced by -OR

Methyl -D-glucopyranoside (methyl -D-glucoside)

O

CH2OH

H

OH

OCH3()H

HOH

OHH

H

OCH2OH

HOHO

OHOCH3()

Haworth projectionChair conformation

Fig 19.UNa, p.475Fig 19.UNb, p.476

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The –OR group of the glycoside may be another monosaccharide – the resulting glycoside is then a disaccharide

Examples of important disaccharides follow:

Maltose

• From malt, the juice of sprouted barley and other cereal grains

O

OHHO

HOCH2OH

OO

OHHO

CH2OH

OH

-1,4-glycoside bond

-maltose because this -OH is beta

beta-maltose

Lactose• The principle sugar present in milk

– about 5% - 8% in human milk, 4% - 5% in cow’s milk

O

OHHO

OHCH2OH

OO

OHHO

CH2OH

OH

-1,4-glycoside bond

-lactose because this -OH is beta

D-galactose unit D-glucose

unit

lactose

Sucrose

• Table sugar, obtained from the juice of sugar cane and sugar beet

O

OHHO

HOCH2OH

O

-1,2-glycoside bond

D-glucopyranose unit

O

CH2OH

HCH2OH

OH H

H HO

1

1

2

D-fructopyranose unit

-2,1-glycoside bond

Cellulose

• Cellulose is a linear polymer of D-glucose units joined by -1,4-glycoside bonds– it has an average molecular weight of 400,000,

corresponding to approximately 2800 D-glucose units per molecule

Starch

• Starch is used for energy storage in plants– it can be separated into two fractions; amylose and

amylopectin. Each on complete hydrolysis gives only D-glucose

– amylose is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by -1,4-glycoside bonds

– amylopectin is a highly branched polymer of D-glucose. Chains consist of 24-30 units of D-glucose joined by -1,4-glycoside bonds and branches created by -1,6-glycoside bonds

Glycogen

• Glycogen is the reserve carbohydrate for animals• Like amylopectin, glycogen is a nonlinear

polymer of D-glucose units joined by -1,4- and -1,6-glycoside bonds bonds

• The total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle

Fig 19.UN, p.487

Heparin is made of sulfonated polysaccharide chains

Fig 19.UN, p.487

Problem 19.67, p.493

Blood Group Substances

• Membranes of animal plasma cells have large numbers of relatively small carbohydrates bound to them

• These membrane-bound carbohydrates are part of the mechanism by which cell types recognize each other; they act as antigenic determinants

• Among the first discovered of these antigenic determinants are the blood group substances