2. Carbohydrate

7/26/2019 2. Carbohydrate

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BIOCHEMISTRY 1

2nd Lecture

CARBOHYDRATE

Structure and functions

Chemistry Education Department-UPI



Biochemistry

Why do we need carbohydrate?

• To give us energy



Biochemistry

I (CH2O)n or H - C - OH

I

Carbohydrates (glycans) have the following basic composition:

Cx(H2O)y

Hydrated carbon!



Biochemistry

• Many carbohydrates are soluble in water.

• The usual chemical test for the simpler

carbohydrates is heating with Benedict’s

solution.

• The formula for a carbohydrate is

(CH2O)n

• The n represents the number of times theCH2O unite is repeated.

rbohydr tes



Biochemistry

• They are of major importance to both plants and

animals. More that half of all organic carbonatoms in the world are in carbohydrate

molecules.

• They are made by chlorophyll-containing plants

in the process of photosynthesis.

6CO2 + 6H2O → C6H12O6 + 6O2

• Our bodies use carbohydrates for energy and

also as a source of carbon atoms for the

synthesis of many other compounds.



Carbon Cycles

6CO2 + 6H2O

CO2 C6H12O6+ 6O2

C6H12O6+ 6O2

6CO2 + 6H2O

C6H12O6+ 6O2



Biochemistry

• They are polyhydroxy aldehydes or ketones, or

compounds that yield polyhydroxy aldehydes or

ketones on hydrolysis.

• They Are Split Into Three Groups Known As:

Monosaccharides (Monomers) -

Oligosaccharides -

Polysaccharides (Polymers) -



Biochemistry

Classification of carbohydrates

• Monosaccharides (monoses or glycoses)simple sugars with multiple OH groups. Based on number of carbons (3, 4, 5, 6),a monosaccharide is a triose, tetrose, pentose or hexose.

• Oligosaccharides

a few monosaccharides covalently linked.

• di, tri, tetra, penta, up to 9 or 10

• Most important are the disaccharides

• Polysaccharides or glycans

polymers consisting of chains of monosaccharide or disaccharide units.

• Homopolysaccharides• Heteropolysaccharides

• Complex carbohydrates



Biochemistry

Monosaccharides

• also known as simple sugars• classified by

1. the number of carbons and

2. whether aldoses or ketoses

• most (99%) are straight chain compounds

• D-glyceraldehyde is the simplest of the aldoses (aldotriose)

• all other sugars have the ending ose (glucose, galactose,

ribose, lactose, etc…)



Biochemistry

C

C

CH2OH

OH)n(H

O

H

Aldose

C

C

CH2OH

OHH

O

H

Aldotriose

n = 1

C

CH2OH

OHH

C O

H

C OHH

Aldotetrose

n = 2

C

CH2OH

OHH

C O

H

C OHH

C OHH

Aldopentose n = 3

C O

H

C OHH

C OHH

CH OH

C

CH2OH

OHH

Aldohexose

n = 4

Aldose sugars



Biochemistry

C

C

CH2OH

OH)n(H

O

CH2OH

Ketose

CH2OH

C O

CH2OH

Ketotriose

n = 0

CH2OH

C O

C OHH

CH2OH

Ketotetrose

n = 1

C OHH

CH2OH

CH2OH

C O

C OHH

Ketopentose

n = 2C OHH

CH2OH

CH2OH

C O

C OHH

OHH

Ketohexose

n = 3

Ketose sugars



Biochemistry

Structure of a simple aldose and ketose



Biochemistry

CONCEPTS OF ISOMERS

Two or more different compounds which contain the

same number and types of atoms and the same

molecular weights.

Projection formula (spatial arrangement to represent 3-

dimensional structure):



Biochemistry

D vs L Designation

• D & L designations are based

on the configuration about the

single asymmetric C in

glyceraldehyde.

• The lower representations are

Fischer Projections.

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

L-glyceraldehydeD-glyceraldehyde

L-glyceraldehydeD-glyceraldehyde



Biochemistry

Sugar Nomenclature

For sugars with more than one

chiral center, D or L refers to the

asymmetric C farthest from the

aldehyde or keto group.

Most naturally occurring sugars

are D isomers.

O H O H

C C

H – C – OH HO – C – H

HO – C – H H – C – OH

H – C – OH HO – C – H

H – C – OH HO – C – H

CH2OH CH2OH

D-glucose L-glucose



Biochemistry



Biochemistry

C

CH2OH

OHH

C O

H

C OHH

C

CH2OH

HOH

C O

H

C HOH

these two aldotetroses are enantiomers.

They are stereoisomers that are mirrorimages of each other

C O

H

C HHO

C HHO

CH OH

C

CH2OH

OHH

C O

H

C HHO

C HHO

CHO H

C

CH2OH

OHH

these two aldohexoses are C-4 epimers.

they differ only in the position of the

hydroxyl group on one asymmetric carbo

(carbon 4)

Enantiomers and epimers

i h i



Biochemistry

Sugar Properties

• Differences in structures of sugars are responsiblefor variations in properties

• Physical

• Crystalline form; solubility; rotatory power

• Chemical

• Reactions (oxidations, reductions, condensations)

• Physiological

• Nutritive value (human, bacterial); sweetness;absorption



Bi h i



Biochemistry

Bi h i t



Biochemistry

Bi h i t



Biochemistry

Cyclic Structure of Monosaccharides

Hemiacetal Formation

anomer anomer

The specific rotation of pure -D-glucose or -D-glucose

changes over time to reach an equilibrium (mutarotation)





Biochemistry



Biochemistry

Intramolecular hemiacetal formation results in two C(1)

stereoisomers called anomers.

On the sameside as

attacking OH, is

-anomer!

On the opposite

side as

attacking OH, is

-anomer!

Biochemistry



Biochemistry

Ring Formation (Glucose)

These are all Glucose

Memorize this structure





Biochemistry



Biochemistry

Biochemistry



Biochemistry

Biochemistry



Biochemistry

Reactions of monosaccharides

• Carbonyl reactions:• Osazone formation

• Cyanohydrin reaction

• Reduction

• Oxidation• Action of base

• Action of acid

• Ring chain tautomerism

• Alcohol reactions• Glycoside formation

• Ether formation

• Ester formation





Biochemistry



Biochemistry

Disaccharide Synthesis

The reactions, the names of the sugars, and whether they

are mono- or disaccharides is what you should know (also,

“Glycosidic linkage”)







Biochemistry



y

Sugar cane

Sugar beet







Biochemistry



suspensions of amylose

in water adopt a helical

conformation

iodine (I2) can insert in

the middle of the amylosehelix to give a blue color

that is characteristic and

diagnostic for starch







Biochemistry



Linear structures of cellulose and chitin

(2 most abundant polysaccharides)

Biochemistry



Glycogen

• also known as animal starch• stored in muscle and liver

• present in cells as granules (high MW)

• contains both (1,4) links and (1,6) branches atevery 8 to 12 glucose unit

• complete hydrolysis yields glucose

• glycogen and iodine gives a red-violet color

• hydrolyzed by both and -amylases and byglycogen phosphorylase



















Biochemistry



Sugar alcohols are very useful

intermediates• Mannitol is used as an osmotic diuretic

• Glycerol is used as a humectant and can be nitrated tonitroglycerin

• Sorbitol can be dehydrated to tetrahydropyrans andtetrahydrofuran compounds (sorbitans)

• Sorbitans are converted to detergents known as spans andtweens (used in emulsification procedures)

Biochemistry



Sugar derivatives

amino sugar - an amino group substitutes for a hydroxyl. Anexample is glucosamine.

The amino group may be acetylated, as in N -acetylglucosamine.

H O

OH

H

OH

H

NH2H

OH

CH2OH

H

-D-glucosamine

H O

OH

H

OH

H

NH

OH

CH2OH

H

-D- N -acetylglucosamine

C CH3

O

H





Too much …..

Carbohydrate will be convertedinto fat and stored under theskin leading to weight gain!

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2. Carbohydrate