Carbohydrates&Nucleic Acids-grb

7/29/2019 Carbohydrates&Nucleic Acids-grb

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Reactions of carbohydrates

Hemiacetal Formation

Reduction

Oxidation

Osazone Formation

Chain ShorteningChain Lengthening


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Epimerization

In base, H on C2 may be removed to formenolate ion.


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Enediol Rearrangement

In base, the position of the C=O can shift.Chemists use acidic or neutral solutions

of sugars to preserve their identity.


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Reduction of Simple Sugars

C=O of aldoses or ketoses can be reduced to

C-OH by NaBH4 or H2/Ni.

Name the sugar alcohol by adding -itoltothe root name of the sugar.

Reduction ofD-glucose produces

Reduction ofD-fructose produces


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Oxidation by Bromine

Bromine water oxidizes aldehyde, but notketone or alcohol.


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Aldose Oxidation to Aldonic Acids Oxidation of the -CHO group of an aldose to a

-CO2H group can be carried out using Tollens,Benedicts, or Fehlings solutions

Precipitates as

a silver mirror

+

O

O

RCH

Ag(NH3 ) 2+

RCO-

NH4+

Ag

Tollens' solution

NH3 , H2 O +

citrate or

tartrate buffer

Precipitatesas a red solid

++

O

Cu2 +

RCO-

Cu2 O

ORCH


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Ketose Oxidation to Aldonic Acids

2-Ketoses are also oxidized by these reagents

because, under the conditions of the oxidation,2-ketoses equilibrate with isomeric aldoses

An aldoseAn enediolA 2-ketose

CH2 OH

C=O

CH2 OH

C-OH

CH2 OH

CHOH

CHOH

CH2 OH

CHO

(CH OH) n (CH OH) n(CH OH) n


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Oxidation by Tollens Reagent Tollens reagent reacts with aldehyde, but

the base promotes enediol rearrangements,so ketoses react too.

Sugars that give a silver mirror with Tollensare called reducing sugars.

All monosaccharides are reducing sugars


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Nonreducing Sugars

Glycosides are acetals, which stable in base, sothey do not react with Tollens reagent.

Some disaccharides are also acetals.

All polysaccharides are also acetals.


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Oxidation by Nitric Acid

Nitric acid oxidizes both the aldehyde and theterminal alcohol.


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Formation of Glycosides

React the sugar with alcohol in acid.

Since the open chain sugar is in equilibrium with

its - and -hemiacetal, both anomers of the acetal

are formed.

Aglycone is the term used for the group bonded tothe anomeric carbon.


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Ether Formation Convert all -OH groups to -OR, using a

modified Williamson synthesis, afterconverting sugar to acetal, stable in base.


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Ester Formation

Acetic anhydride with pyridine catalyst converts

all the oxygens to acetate esters.


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Osazone Formation

Both C1 and C2 react with phenylhydrazine.


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Osazone


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Ruff Degradation

Aldose chain is shortened by oxidizing thealdehyde to -COOH, then decarboxylation.


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Kiliani-Fischer Synthesis

This process lengthens the aldose chain. A mixture of C2 epimers is formed.


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Determination of Ring Size

Haworth determined the pyranose

structure of glucose in 1926.

The anomeric carbon can be found by

methylation of the -OHs, then hydrolysis.

O

H

OH

H

HO

HO

H

OH

H

C

H

H2OHexcess CH3I

Ag2O O

H

OCH3

H

CH3O

CH3O

H

O

HH

C

CH3

H2OCH3H3O

+

O

H

OH

H

CH3O

CH3O

H

O

HH

C

CH3

H2OCH3


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Periodic Acid Reactions Periodic acid ( HIO4 or H5IO6 ) cleaves the C-C bond

between an alcohol and an adjacent alcohol (vicinal) orcarbonyl group.

Does not affect ethers or acetals.

Two carbonyl compounds are formed:1 alcohols oxidize to formaldehyde

2 alcohols oxidize to aldehydes

aldehydes oxidize to formic acid

ketones oxidize to carboxylic acids

carboxylic acids oxidize to CO2


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Use of Periodic Acid Cleavage

Separation and identification of the products

determine the size of the ring.


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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-Glucose

H2

CHO

CH2 OH

OHH

HHO

OHH

OHH

CH2 OH

CH2 OH

OHH

HHO

OHH

OHH


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You try it:Oxidation of which two hexoses would give the

same product?

H

CHO

OH

HHOOHH

OHH

CH2OH

CHO

CH2OH

d-(+)- glucose

+

H

X

OH

HHO

OHH

OHH

X

Same product


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Question #1

Which of the following aldaric acidsare optically active?

A B C D E


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H

CHO

OH

HHO

OHH

OHH

CH2OH

CHO

CH2OH

d-(+)- glucose

+

H

X

OH

HHOOHH

OHH

X

Same product

Question #2Draw a hexose that would give the same

aldaric acid product as D-Glucose

D

Q i #3


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H O

OHH

OHH

OHH

CH2OH

D-Ribose

Question #3There are four D-aldopentoses. Draw Fischer

projections of each of them. Then draw Fischer

projections of the aldaric acids they would yield.Label each center as a R or S configuration. Circlethe aldaric acids that are optically inactive?

H O

HHO

OHH

OHH

CH2OH

D-Arabinose

H O

OHH

HHO

OHH

CH2OH

D-Xylose

H O

HHO

HHO

OHH

CH2OH

D-Lyxose


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Question #4

Select the compounds that would produce

the same osazone.


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Common Modifications to

monosaccharides

Deoxy sugars

Amino sugars

Glycosides (acetal)


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Deoxy Sugar


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Amino Sugar

Glucosamine

HO O

H

H

HO

H

HNH2H OH

OH



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Formation of Glycosides -

Acetals

A monosaccharide hemiacetal can react with a

second molecule of an alcohol to form an

O

OH

O

OCH3

CH3OH

H+

Gl id


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Glycosides Glycoside bond: the bond from the anomeric carbon

of the glycoside to an -OR group.

Cyclic acetals are notin equilibrium with their openchain carbonyl-containing forms. Glycosides doNOT

undergo mutarotation.

List the name of the alkyl or aryl group attached tooxygen followed by the name of the carbohydrate

with the ending -e replaced by -ide methyl -D-glucopyranoside

methyl -D-ribofuranoside


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O

CH2 OH

HOH

OCH3

()H

HOH

OHH

H

O

CH2 OH

HOHO

OHOCH3 ()

Haworth projection

Chair conformation

Is this a reducing sugar glycoside?


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Disaccharides

Maltose

Lactose

Sucrose

Cellobiose


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Disaccharides

Three naturally occurring glycosidic linkages:

1-4 link: The anomeric carbon is bonded

to oxygen on C4 of second sugar. 1-6 link: The anomeric carbon is bonded

to oxygen on C6 of second sugar.

1-1 link: The anomeric carbons of the twosugars are bonded through an oxygen.

M lt


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Maltose From malt, the juice of sprouted barley and

other cereal grains. (Cellulose)

OHO

HO

OH

CH2OH

CH2OH

OHHO

O

OH

O

Is this a reducing sugar?

4-O-(-D-glucopyranosyl)-D-glucopyranose


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LactoseThe principle sugar present in milk

5% - 8% in humans, 5% in cows milk

D-glucopyranose

OCH2OH

HO

OH OH

OH

HO

O

CH2OHO

OH

D-galactopyranose


4-O-(-D-galactopyranosyl)-D-glucopyranose

Sucrose


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Sucrose Table sugar, obtained from the juice of sugar cane

and sugar beet.

OCH2OH

HOHO

OHO

CH2OH

OH

OH

CH2OH

O


1-O-(-D-galactopyranosyl)- - D-fructofurananosideOR1-O-(- D-fructofurananosyl)- -D-galactopyranoside


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N-Glycosides

The anomeric carbon of a cyclic hemiacetal

undergoes reaction with the N-H group of an

amine to form an N-glycoside

N-glycosides of the following purine and pyrimidine

bases are structural units of nucleic acids

HN

N

O

O

H

N

N

NH 2

O

H

HN

N

O

O

H

CH3

Uracil Thymine Cytosine


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N-Glycosides

N

N N

N

NH2

HAdenine

anomericcarbon

a -N-glycosidebond

H

H

H

OHOCH2

HO OH

NH2

O

N

N

H

HN

N N

N

O

H

H2N

Guanine

F i f N Gl id


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Formation of N-Glycosides

(Nucleosides)

For example, reaction between -D-ribofuranose

and cytosine produces water and cytodine, one of

the structural units of RNA:

OOH

OHOH

HOCH2

N

N

NH2

H

O

+

O

OHOH

HOCH2O

NH2

N

N

-N-glycoside bond

- H2O

-D-Ribofuranose Cytosine

Uridine

anomericcarbon

Cytodine


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Gentiobiose Two glucose

units linked1-6.

Common

carbohydratebranch point


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Polysaccharides

Polysaccharides are chains of five or moremonosaccharide:

Starcha glucose polymer that is the storage carbohydrateused by plants.

Glycogen a glucose polymer that is the storagecarbohydrate used by animals.

Cellulosea glucose polymer that is a major component ofthe cell wall in plants & algae.

Agar

natural component of certain seaweed polymer ofgalactose & sulfur containing carbohydrates.

Chitinpolymer of glucosamine (a sugar with an aminofunctional group).


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Starch

Starch is used for energy storage in plants

it can be separated into two fractions; amylose andamylopectin. Each on complete hydrolysis givesonly 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 andbranches created by -1,6-glycoside bonds


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AmylopectinO

CH2OH

HO

OH

O

O

OCH

2

HO

OH

O

O

O

OH

HO

CH2OHO

OCH2OH

HO

OHO

O

OH

HO

CH2OHO


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Glycogen

The reserve carbohydrate for animals

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


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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


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Cellulose


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Polysaccharides Digestion

Polymers of Glucose

Starch is digestable

Cellulose is notdigestable by humans


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Modification of Cellulose Cellulose Nitrate called guncotton

PyroxylinPartially nitrated

photographic film and lacquers Cellulose Acetate film explosive

Cellulose reprocessed Rayon via

carbon disulfide


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Cellulose fibre - Rayon

Cellulose OH Cellulose O-Na+NaOH

Cellulose OCS-Na+

SS C S

Sodium salt of a xanthate ester

H+

spinneretCellulose OH

Cellulose fibre


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Membrane Carbohydrates Membranes of animal plasma cells have large

numbers of relatively small carbohydrates boundto them

these membrane-bound carbohydrates are part of the

mechanism by which cell types recognize each other;they act as antigenic determinants

Early discovery of these antigenic determinants are

theblood group substances


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ABO Blood Classification

In the ABO system, individuals are

classified according to four blood types:

A, B, AB, and O at the cellular level, the biochemical basis for

this classification is a group of relatively small

membrane-bound carbohydrates

ABO Bl d Cl ifi i


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ABO Blood Classification

NAGal Gal NAGluCell membrane

of erythrocyte

-1,4-) -1,3-) -1-)

Fuc

-1,2-)NAGal = N-acetyl-D-galactosamine

Gal = D-galactose

NAGlu = N-acetyl-D-glucosamineFuc = L-fucose

missing in

type O blood

D-galactose intype B blood


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ABO and Disease

A

Syphilis, Smallpox, Bronchial Pneumonia, RhuematicHeart Disease

B

Infantile Diarrhea, Typhoid Fever, Scarlet Fever

O

Bubonic Plague, Paratyphoid, Scarlet Fever, Cholera

Some infectious disease organisms have ABO antigens on

their cell walls conferring resistance to those that can producethe antibodies and increases the susceptibility of those whose

blood type matches the antigens.

Glucose Assay


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Glucose Assay The glucose oxidase method is completely

specific for D-glucose

+

+

glucose

oxidase

D-Gluconic acid

Hydrogen

peroxide

- D-GlucopyranoseOH

OH

HOHO

CH2 OHO

H2 O2

O2 + H2 O

CO2 H

CH2 OH

OHH

HHO

OHHOHH

Chemstrip Kit


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Chemstrip Kit

Blood glucose test for diabetics

Based on reaction of o-toluidine with glucose

CHO

OHH

HO H

OHH

OHH

CH2OH

H2N

H3C

CH

OHHHO H

OHH

OHH

CH2OH

N

H3C

peroxidase +colored product+o-toluidine H2 O2 H2 O


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Biosynthesis with Glucose


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Cellulose

Polymer ofD-glucose, found in plants.

Mammals lack the -glycosidase enzyme.


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Amylose Soluble starch, polymer ofD-glucose.

Starch-iodide complex, deep blue.

A l ti


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Amylopectin

Branched, insoluble fraction of starch.


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Glycogen

Glucose polymer, similar to amylopectin, buteven more highly branched.

Energy storage in muscle tissue and liver.

The many branched ends provide a quick

means of putting glucose into the blood.


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Chitin

Polymer ofN-acetylglucosamine.

Exoskeleton of insects.


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Nucleic Acids

Polymer of ribofuranoside

rings linked by phosphate

ester groups.

Each ribose is bonded to a

base.

Ribonucleic acid (RNA)

Deoxyribonucleic acid

(DNA)


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Ribonucleosides

A -D-ribofuranoside bonded to a heterocyclicbase at the anomeric carbon.


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Ribonucleotides

Add phosphate at 5 carbon.

f


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Structure of RNA


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Structure of DNA

-D-2-deoxyribofuranose is the sugar.

Heterocyclic bases are cytosine, thymine

(instead of uracil), adenine, and guanine. Linked by phosphate ester groups to form

the primary structure.


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Base Pairings


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Double Helix of DNA

Two complementary

polynucleotide chains

are coiled into a helix.

Described by Watsonand Crick, 1953.

DNA R li i


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DNA Replication


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Additional Nucleotides

Adenosine monophosphate (AMP), a

regulatory hormone.

Nicotinamide adenine dinucleotide (NAD),a coenzyme.

Adenosine triphosphate (ATP), an energy

source.

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