Structure

1
Structure Function of Carbohydrates

• Lectures 1-3 MBC226-222-241-224
• Dr Ayyub Patel
• ?To lecture 2 ?To lecture 3

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2
Overview Objectives

• Define Mono, Di and Polysaccharides
• Recall Structure and Function of Glucose
• Recognize CHO Isomers
• Describe Structure and Function of the Important
  Monosaccharide Derivatives
• Describe Structure and Function of Starch,
  Glycogen, Cellulose and Chitin
• Recall the general contents of Mucopolysaccharides
  , proteoglycan and glycoprotein and their
  importance

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3
Carbohydrates (CHO)
Molecules whose formula can be expressed in terms
of C and H2O Glucose is C6(H2O)6 Sucrose
is C6(H2O)11 More complex CHO such as Starch
and Cellulose are polymers of Glucose with
general formula Cn(H2O)n-1 CHO are either
Polyhydroxylaldehydes or
Polyhydroxylketones
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4
Mono Di and Polysaccharides
CHO are classified according to the number of
units obtained upon hydrolysis of one
molecule Monosaccharides are CHO that cannot be
hydrolyzed to obtain smaller molecules of
CHO Glucose is well known monosaccharide The
difference between mono, di and polysaccharides
can be understood from the following diagram
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5
Monosaccharides

• Subdivided according to the Number of C atoms
• Triose, teroses, pentoses, hexoses etc..
• http//www.scientificpsychic.com/fitness/carbohydr
  ates.html

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Harper 25th Ed. Table 15.1 Classification of
imp. sugars
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Some Monosaccharides
Note Numerous Chiral Carbons
Want to see that again?
Hence Carbo (C) Hydrate (H2O)
Note Basic Formula (CH2O)n
Want to see that again?
7
Glucose

• Most important because it is a major fuel
• It can be converted to other CHO with highly
  specific functions
• Such as Glycogen for Storage
• Ribose and deoxyribose for Nucleic Acid formation
  
• Galactose for formation of lactose in milk
• Also shares in formation of glycolipids,
  proteoglycans and glycoproteins

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Glucose

• Straigh chain formula accounts for some of its
  properties but the cyclic structure (Pyran or
  Furan see Fig 15.3) is more favoured on
  thermodynamic grounds
• In solution it is 99 in pyranose form

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9
Glucose

• Dextro () and levo (-) rotatory isomers. Ie
  solutions of molecules having 4 different groups
  around C will rotate polarised light to right,
  dextrorotatory () or left, levorotatory (-)
• In solution glucose is mainly dextrorotatory
  hence it is called DEXTROSE. But Fructose is levo
  (-)

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10
Glucose

• Alpha and Beta anomers
• When the OH groups of active C is at right side
  (down) it forms Alpha-anomer but when the OH is
  on left side it forms Beta-anomer Fig 15.5 or
  see below

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11
Glucose

• Variations in cofiguration of the OH and H on
  carbons 2, 3 and 4 give rise to epimers
• Eg. Galactose and mannose Fig 15.6

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• Aldose Ketose Isomers
• Both Glucose and Fructose are C6H12O6 but
  different structures, Aldosugar (Glucose) and
  Ketosugar (Fructose)

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Stable Monosaccharide Rings
So, what is this molecule?
Answer It is ?-D-Glucose
(including the numbering)
For the exam, draw it from memory!
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Other Monosaccharides
Other Monosaccharides of physiological importance
are Trioses Glyceraldehyde
anddihydroxyacetone important intermediates in
glycolysis and other pathways Tetroses
Erythrose intermediate in PPP Pentoses
D-ribose structural importance in NA and
coenzymes ribose phosphates intermediates in PPP
(see Table 15.2) Hexoses D-Glucose, D-Fructose,
D-Galactose, D-Mannose (see table 15.3 for
importance)
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14
Linkage of monosaccharides Maltose a
disaccharide
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?-D-Glucose
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Disaccharide Synthesis
Energy
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Glucose / Maltose / Amylose
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2 glucose molecules linked by an ?-1,4-glycosidic
bond
C6
C1
C6
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Common disaccharides
Common dietary components
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Sucrose (table sugar from cane or beet)
Hydrolyzed by sucrase
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Lactose (from milk)
Hydrolyzed by lactase in humans, by
?-galactosidase in bacteria
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Maltose (from starch hydrolysis)
Hydrolyzed by maltase
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Polysaccharides Glycogen (branch points)
Glucose store
Glycogen is highly branched
Branch every 10 glucose units (approx)
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Glycosidic bonds determine structure
Straight chains, good for structure
Bent chains, good for storage
25
Cellulose
Major structural polymer of plants, one of the
most abundant organic compounds in the biosphere
Straight chain polymer of glucose, Fibrils formed
by parallel chains, held by hydrogen bonds
Mammals lack cellulases, cannot digest wood or
vegetable fibers, bacteria hydrolyze it in the
rumen
26
Starch glycogen (homopolymers)
Open helix, accessible stores of sugar,starch in
plants, glycogen in animals
Glycogen, highly branched, (every 10 glucose
units)
Starch, two forms, Amylose - unbranched, Amylopect
in - branched (every 30 glucose units)
27
Glycosaminoglycans, Anionic polysaccharides
Made of repeating disaccharide units, containing
a derivative of an amino sugar, glucosamine or
galactosamine
At least 1 of the sugars has a negatively charged
carboxyl or sulfate group
Usually attached to proteins to form proteoglycan
(95 carb)
28
Proteoglycan functions
Lubricants for mucous membranes connective
tissue Structural components in connective
tissue Mediate adhesion of cells to
extracellular matrix Bind factors that
stimulate cell proliferation
29
Chondroitin 6-sufate
Found in cartilage
30
Keratan sulfate
Found in hair, nails, etc
31
Heparin
Anticoagulant used to prevent blood clotting
32
Dermatan sulfate
Found in skin
33
Hyaluronate
Found in connective tissue serves as lubricant