Download 302-5-carbohydrates

Carbohydrates
Important Monosaccharides
Contents
Important monosaccharides
Monosaccharide derivatives
 Uronic acid
 Amino sugars
 Deoxysugars
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Glucose
Originally called dextrose.
Primary fuel for living organisms.
Source of energy fro brain cells and cells that have few or
no mitochondria eg RBCs.
Sources- Plant starch, disaccharides like lactose, maltose,
sucrose
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Glucose - Structure
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Fructose
D- fructose originally called levulose is also called fruit
sugar.
Also found in some vegetbles and honey.
It is also used in male reproductive tract. It is synthesized
in sminal vesicle and then incorporated into semen.
Sperm use it as the source of energy.
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Fructose - Structure
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Galactose
Is needed to synthesize various biomolecules like lactose
by mammary glands, glycolipids, certain phospholipids,
glycoproteins etc.
Galactose and glucose are epimers at carbon 4.
Their interconversion is catalysed by epimerase.
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Galactose - Structure
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Monosaccharide Derivatives
Uronic acids
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Two uronic acids are important in mammals.
D-Glucuronic acid and its epimer L-iduronic acid.
In liver glucuronic acid is used for conjugation of drugs,
steroids and bilirubin.
Both D-glucuronic acid and its L-iduronic acid are
abubdant in connective tissue.
Glucoronic acid
L-iduronic acid
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Amino Sugars
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The hydroxyl group commonly on carbon 2 is replced by
an amino group.
They are constituents of complex carbohydrate
molecules found attached to cellular lipids and proteins.
Example: D-glucosamine and D-galactosamine.
In N-acetyl amino sugars the amino group itself carries an
acetyl group (CH3 —CO —) as a substituent. eg. Nacetyl-β-D-glucosamine and its derivative N-acetyl-βmuramic acid which has an added carboxylic side chain.
These two compounds are components of bacterial cell
walls.
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N-acetylneuraminic acid (common form of sialic acid) is a
condensation product of D-mannosamine and pyruvic
acid.
Sialic acids are common constituents of glycoproteins and
glycolipids.
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Deoxy Sugars
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Monosaccharides in which an –H has been replaced by an
–OH group are called as deoxy sugars.
Two important deoxy sugars are L-fucose (formed from
D-mannose by reduction reactions) and 2-deoxy-Dribose.
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Fucose is found among carbohydrate components of
glycoproteins such as ABO group determinants on the
surface of RBCs.
2-Deoxyribose is a pentose component of DNA.
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Sugar Derivatives
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Sugar Derivatives
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