Carbohydrates all have CO and OH functional groups'

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Review

• Carbohydrates all have CO and -OH functional
  groups.
• Classified based on
• Size of carbon chain
• Number of sugar units
• Location of CO
• Stereochemistry

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Monosaccharides General formula (CH2O)n. n
number of carbon.
Most monosaccharides in nature contain 3 - 7
Carbons (triose, tetrose, pentose, hexose, and
heptose).
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• Aldose - aldehyde sugar
• Carbonyl group (CO) at the first carbon
• position, which forms an aldehyde group
• (CHO).
• Ketose - ketone sugar
• Carbonyl group is at C2 position

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H CO H-
C-OH H- C-OH H- C-OH
CH2OH
CH2OH CO
HO- C-H H- C-OH H-
C-OH CH2OH
Aldose Ketose (- CHO) (- CO)
(Based on the location of CO)
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Glyceraldehyde, an aldotriose, is the smallest
monosaccharide.
H CO
H-C-OH CH2OH
Chiral center
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Any other sugars with same configuration as
D-glyceraldehyde is classified as D sugar,
otherwise L sugar.
Note, the chiral center farthest from the
carbonyl carbon determines D or L forms of a
sugar.
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Carbohydrates in cyclic structures

• Monohydrates with five C or more spend most
  time in cyclic structure.

• When the aldehyde or ketone groups interact
• with the -OH in the other end of the molecule,
• a ring is formed.
• aldehyde ? hemiacetal
• ketone ? hemiketal

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Haworth projection is often used to
describe cyclic structure of monosaccharide.
CH
OH
2
H
O
H
C1
H
H
OH
OH
OH
OH
H
? -D-glucose
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? -D - glucose
CH
OH
2
O
OH
H
? - D - glucose
H
H
OH
OH
H
H
OH
In solution, D-glucose exists in a mixture of
three forms, 33 of ? rings, 66 of ? ring and
1 of open chain.
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• This can also happen
• to ketose (fructose).

CH2OH
CH
OH
2
O
H
OH
???
OH
CH
2
H
OH
C
O
H
OH
C
H
HO
C
OH
H
C
OH
H
OH
CH
OH
2
O
CH
OH
H
OH
2
???
H
CH2OH
H
OH
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Reactions of glucose and other monosaccharides

• Oxidation-Reduction. Required for their complete
  metabolic breakdown.
• Esterification. React with acid to form esters.
• Amino derivatives.
• Glycoside formation - Linkage of monosaccharides
  to form polysaccharides.

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In a redox reaction, if one reactant is oxidized,
the other must be reduced. The molecule that
gains O or loses H (glucose) is called a
reducing agent. The molecule that gains H or
loses O is an oxidizing agent.
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In a redox reaction, an aldehyde sugar will gain
an O and becomes oxidized (-COH ? COOH). In
the mean time, it acts as a reducing agent to
make the other reactant reduced (Cu ? Cu, or
NAD ? NADH).
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In aerobic respiration pathways, the enzyme that
catalyzes redox reactions is dehydrogenase, which
uses NAD and NADH as coenzymes. NAD - an
oxidizing agent that can receive
electrons. NADH - a reducing agent that can
donate electrons. NAD 2e NADH H
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2). Esterification (phosphorylation) When -OH
group in an alcohol or carbohydrate react with
phosphoric acid, phosphate esters can be
produced.  
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In a living cell, phosphate esters are not
produced by acid, instead, by transferring
phosphoryl (P) group form ATP to a carbohydrate
molecule. and the reaction is catalyzed by
kinases.  

• Example
• D-glucose ATP glucose-6-P ADP

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3). Amino Derivatives of Sugars
The replacement of a hydroxyl group on a
carbohydrate results in an amino sugar.
O
O
OH
OH
H
H
H
H
H
H
OH
OH
H
H
OH
OH
H
OH
H
?-D-glucose ?-D-2-aminoglucose

(glucosamine)
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Two naturally occurred amino sugars are
D-2-aminoglucose (glucosamine) and
D-2-aminogalactose (galactosamine).
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• Functions of amino sugars.
• Structural components of bacterial cell walls.
• (N-acetylglusamine and N-acetylmuramic acid)
• As a component of exoskeleton of some organisms.
  (Chitin)

• Chondroitin sulfate, a derivative of
  glucosamine,
• is a component of cartilage.
• Component of glycoprotein and glycolipids.

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4). Glycoside Formation An O-glycosidic bond
can be formed between two monosaccharides, when
two -OH groups react with each other. The
product is called a glycoside.  
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Glycosidic bonds
Type is based on the position of the C-1 OH ?
glycosidic bond - linkage between a C-1 ? OH
and a C-4 OH ? glycosidic bond - linkage
between a C-1 ? OH and a C-4 OH ?
bonds ? bonds
C-4 end can be either up or down depending on the
orientation of the monosaccharide.
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• Lactose - dimer of ?-D-galactose and either ?
  or ? - D-glucose.

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?-Maltose
?-D-glucose and ?-D-glucose, ? (1 4)
linkage.
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Sucrose

• Disaccharide of ?-glucose and
  ?-fructose.

An unique linkage
??? (1 2) linkage
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CH2OH CO
HO-C-H H-C-OH
H-C-OH CH2OH
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• Polysaccharides
• Carbohydrate polymers
• - Chains of monosaccharides linked up by
• O-glycosidic bonds.
• Different polysaccharides starch, glycogen,
• cellulose, which have different length degree
• of branching sequence of the monosaccharides
• and types of glycosidic bonds.
•  

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Functions of Polysaccharides

• Energy storage - starch and glycogen
• Structural materials
• Cellulose in plant cell wall.
• Peptidoglycans in bacterial cell walls

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1. Starch (storage polysaccharide)

• Energy storage in plants
• Long repeating chain of ?-D-glucose
• (up to 4000 units)
• Insoluble

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• Starch is the mixture of amylose and amylopectin
• Amylose - major form of starch, straight chain
• of glucose linked up by ?(1? 4) glycosidic
• bonds.
• Amylopectin - branched structure with side
• chains linked by ?(1? 6) glycosidic bonds.

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Amylose

• Straight chain that forms coils ? (1 4)
  linkage.

Amylase is the enzyme that digests amylose.
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Amylopectin

• Branched structure due to crosslinks.

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2. Glycogen polymer of glucose

• Energy storage of animals (animal starch).
• Stored in liver and muscles as granules.
• Highly branched polymer, similar to amylopectin.
• but bigger, with more (1-6) bonds

? (1 6) linkage at crosslink
c
c
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The enzyme glycogen phosphorylase is the enzyme
that cleaves glucose from glycogen for energy
supply.
The activity of glycogen phosphorylase
is regulated by phosphorylation.
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Other forms of storage polysaccharides Dextran
(produced by bacteria, highly viscous), Polymer
of glucose linked by ?(1?6) linkage with
branches formed by ?(1 ?2), ? (1 ? 3), ? (1 ?
4)bonds. Inulin- polymer of D-fructose linked by
(2? 1) Bonds, found in vegetables.
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 3. Cellulose (structural polysaccharide) Structu
ral component of wood and plant
fibers. Cellulose is an unbranced polymer of
glucose linked up by ? (1?4) glycosidic bond.  
Many long cellulose chains lined up in a parallel
arrangement and associate with each other
through H-bonds. The bundles of cellulose form
strong and rigid frameworks that provides
physical support for plant cells.
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Cellulose

• Most abundant polysaccharide.
• ? (1 4) glycosidic linkages.
• Result in long fibers - for plant structure.

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Celullase, the enzyme that digest ? (1-4)
glycosidic bonds between glucoses, is produced
by some fungi, bacteria and termites. These
organisms can extract glucose for nutrition
supply.
Cattle, sheep, goats can also use cellulose
to extract glucose Humans ?
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4. Structural peptidoglycans

• Bacterial cell walls are composed of unbranched
  polymer of alternating units of
  N-acetylglucosamine and N-acetylmuramic acid.

CH
R
O
L-Ala
D-Isoglu
L-Lys
D-Ala
Peptide crosslink
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• Polymer of N-acetylgluco-
• samine and N-acetylmuramic
• acid crosslinked with
• peptide bridges

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5. Mucopolysaccharides

• These materials provide a thin, viscous,
  jelly-like coating to cells extracellular
  matrix.
• The most abundant form is
• hyaluronic acid.

O
O
H
H
H
OH
O
H
NH
O
H
C
O
HO
H
O
O
H
H
H
OH
H
H
OH
O
H
NH
O
H
C
O
HO
H
O
H
O
H
OH
H
H
H
OH
Alternating units of N-acetylglucosamine and
D-glucuronic acid.
O
H
NH
O
H
C
O
HO
H
H
OH
H
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Glycoproteins

• Proteins that carry covalently bound carbohydrate
  units.
• Biological functions serve as cell surface
  marker to be involved in
• immunological protection
• cell-cell recognition
• blood clotting
• host-pathogen interaction

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Glycoprotein structure

• Linkage between sugars and proteins
• O-glycosidic bonds using hydroxyl groups of
• serine and threonine
• N-glycosidic bonds
• using side chain amide
• nitrogen of asparagine residue

threonine
polypeptide chain
asparagine
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• Carbohydrates only account for 1-30 of the total
  weight of a glycoprotein.
• The most common monosaccharides are
• glucose
• galactose
• sialic acid
• N-acetylgalactosamine
• N-acetylglucosamine

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Carbohydrates are information rich
molecules. For example, terminal carbohydrate
residues on a glycoproteins serve as a signal
that directs liver cells to remove the protein
from the blood. Many newly synthesized
glycoproteins (immunoglo- bulins and peptide
hormones) contain carbohydrates with terminal
sialic acid, which is removed by sialylases over
hour or days. The trimmed glycoproteins are
detected by the liver cells and are removed from
blood.
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Asialoglycoprotein binds with asialoglycoprotein
receptor on liver cell surface and gets to be
internalized through endocytosis
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These polysaccharide units mark the passage of
time to indicate when the protein carrying them
should be removed from circulation. The rate
of the removal of sialic acid is controlled by
the structure of the protein. Proteins can be
designed to have lifetime ranging from hours to
weeks, depending on the needs
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Carbohydrates are also critical in the
interaction of sperm and egg. Ovulated eggs are
covered with extracellular matrix called zona
pellucida, which contains oligosaccharides,
hyaluronic acid. A glycoportien in this coat
is recognized by a membrane receptor of sperm.
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The binding triggers the release of sperm
enzyme, protease and hyaluronicdase that dissolve
the zona pellucida to allow sperm entry.