Why Carbohydrates ?

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Structure of sugars
Tehran University of Medical Sciences
Parvin Pasalar Arsia Jamali
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Why Carbohydrates ?
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Sugars

• Objectives After studying this session you have
  to
• Define what a carbohydrate molecule is
• Recognise and classify carbohydrate molecules
• Explain why carbohydrates are important
• Explain different types of isomerism in
  monosaccharides
• Name other molecules that interact with
  carbohydrates and explain how and why these
  interactions occur
• Know different names, roles, definitions,
  structurs and classifications of sugars, MS,
  OS(DS) PS

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Sugars/ Importance

• 1. Photosynthesis energy stored in carbohydrates
• 2. The most abundant organic molecules in nature
• 3. Metabolic precursors of all other
  biomolecules
• 4. Central in the metabolism of plants and
  animals
• 5. Important structural component of plants
  (cellulose, pectate), animals (hyaloronic acid,
  chitin) and bacterial cells (murein)

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Sugars/ Importance
Sugars/ Importance

• 6. Fuel In animals, they represent a major
  part of the caloric intake.
• 7. Energy Storage ( glycogen, starch, inulin).
• 8. Cell-cell recognition
• 9. Adhesion (hyaluronic acid)
• 10. They are important in immune responses
  either as antigenic determinants or antibody
  structure
• 11. Protein ageing ( non-enzymatic glycation)
• 12. Age determinant in some protein and cells
  (Asialo glycoprotein)

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Sugars/ Different names and definition

• 1- Carbohydrates Cn(H2O)n Substances with
  equal ratio of carbon atom and water.
• Exceptions
• Sugars that have not the formula
  (deoxyribose Fucose)
• Substances that are not sugars but have
  the formula formaldehyde (C H2O) lactic acid
  C3(H2O)3

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Sugars/ Different names and definition

• 2- Glucides ( glycos Gk. sweet) OR
• Saccharides ( sakcharon Gk. sugar)
• Exceptions
• Sugars that are not sweet (cellulose
  starch)
• Sweet substances that are not sugars
  (glycerol, monilin, aspartam and saccharine)
• 3- Ose ( suffix from Fr. sugar)
• 4- Definition Polyhydroxy compound with an
  aldehyde or a ketone group or those compounds
  that by hydrolysis produce such compounds.

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Sugars

• Different classifications
• 1- With respect to the number of building blocks
  they are classified into three groups
• a-Monosaccharide (mono one) or
  simple sugar have just one unit.
• b-Oligosaccharide (oligo few) that
  are composed of 2-10 Monosaccharide units
• c-Polysaccharides (poly many) are
  much larger sugars , containing hundreds of
  monosaccharide units
• 2- With respect being pure sugar or having other
  components are classified into
• a- Glycoprotein Proteoglycane
• b- glycolipid and
  lipopolysccharide.

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Monosaccharides

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Sugars/General idea

• The simplest sugar is Glyceraldehyde.
• All other simple sugars are derived from
  Glyceraldehyde.
• The structure of Glyceraldehyde is the basis of
  sugar classification into two different D or L
  classes.

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Sugars/General idea

• They have asymmetric (chiral) carbon.
• The only sugar that has not any
• assymetric carbon is dihydroxyacetone.
• Glucose ( dextrose) is the reference sugar in
  medical sciences and is the most abundant sugar
  that is present and used as the fuel in all
  living organisms.

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MS/ Different definitions

• They are called simple sugar, because by
  hydrolysis they can not make any other simpler
  sugars.
• They are called Polyhydroxyaldehyde or
  Polyhydroxyketone.
• In other words
• They are Polyhydroxy compound with an aldehyde or
  a ketone group.

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Monosaccharides

• Different Classifications and nomenclatures
• 1- On the basis of the numbers of carbon atoms
  Triose, tetrose, pentose, hexose and heptose.
• 2- On the basis of the functional group Aldose
  and ketose. In most cases the name of a ketose is
  make by addition of ul between the name of
  sugar and ose. Example Ribose and ribulose,
  heptose and heptulose.
• 3-On the basis of both above properties
  Aldotriose, ketotriose.

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Monosaccharides

• Different properties and roles
• 1- They are composed of 3-7 (3-8) carbon atoms
• 2-All are soluble, reducing and easily can make
  crystal.
• 3- D- family sugars are the most abundant sugars
  in the living organism.
• 4-Because of the functional groups (aldo, keto
  and hydroxyl groups they are reactive compounds

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MS/ Different properties and roles

• 6- By becoming cyclic, 5-7 carbon sugars are
  called internal hemiacetal or hemiketal. In other
  words they are produced by joining of the
  functional group with a hydroxyl group of same
  molecule.
• 7- By combination they make oligo and
  polysaccharides.
• 8-There are different isomerisms for the MS

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MS/ Asymmetric (chiral) carbon
Chiral means like hands. It is referred to a
carbon atom with 4 different groups linked to it.
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Two different 1- methyl glucoside of Glc !
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Sugars/ General structure/ Cyclization
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Sugars/ Cyclic (Ring) structure

• A Haworth projection

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Monosaccharides

• Different isomerisms
• Functional
• Ring
• Optic

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MS/ isomerisms/1- Functional

• Aldose is referred to those simple sugars that
  have an aldehyde group as their functional group.
• Ketose is referred to those simple sugars that
  have an ketone group as their functional group.

Aldose to ketose conversion by enediol
intermediate
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MS/ isomerisms/Functional
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MS/ isomerisms/ 2- Ring

• By the linking of functional group to a
  hydroxyl group, 4-7 carbon sugars make a furan or
  pyran like rings. In this way, the carbon of
  functional group is called anomeric carbon.
• Pyranose is a six member ring
• sugar that may be in chair
• or boat conformation.
• Furanose is a five member ring
• sugar that its conformation
• is like a letter envelope.
• Note that Linear and cyclic sugars are
  isomers.

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MS/ Isomerisms
Conformational
Ring
Furanose/ Pyranose
Chair/ Boat
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MS/ isomerisms/3- Optic or Steroisomerism

• It is because of the presence of asymmetric
  carbon atom and is classified into four types
• D L
• Enantiomerism
• Epimerism
• Anomerism

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MS/ isomerisms/Streoisomerism(Optic)
a- Enantiomerism b- Epimerism c- Anomerism
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MS/ isomerisms/3- Optic/ 1- D L

• D L do not refer to the rotation of
  polarized light, but are stand for the family of
  the sugar. For showing the rotation of polarized
  light () or (- )sign are used.
• D- family sugars are abundant, natural
  sugars that are derived from D- glyceraldehyde so
  the OH group of the last asymmetric atom is at
  right.
• L- family sugars are rear sugars and just
  found in the oligosaccharides present as
  antigenic moieties. They can not be metabolized
  and make energy. The OH group of the last
  asymmetric atom is at left.

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MS/ isomerisms/3- Optic/ 2- Enantiomerism (
mirror image)

• Definition
• All OH groups have opposite orientation
• A pair of enantiomers have same name, but are
  shown with D or L letters .
• They rotate polarized light equally into two
  opposite directions, if one is D(-) the other one
  will be L().
• Example D() Glc L(-) Glc or D()Fru
  L(-) Fru

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MS/ isomerisms/3- Optic/ 3- Epimerism

• Definition The difference between the OH
  orientation of just one asymmetric carbon atom
  other than the last one (the one that determines
  the family of a sugar).
• Example
• Mannose ( epimer 2 Glc)
• Allose ( epimer 3 Glc)
• Galactose ( epimer 4 Glc)

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MS/ isomerisms/3- Optic/ 4- Anomerism

• Definition
• OH orientation of anomeric carbon is the
  basis of this classification.
• ß anomer Same orientation with the side
  chain
• ( the last carbon atom)
• a anomer opposit orientation with the
  side chain
• Example a or ß anomer of D()Glc.

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MS/ isomerisms/ optic / Mutarotaion

• Mutarotaion a or ß anomer can convert to each
  other via an open chain intermediate. In doing so
  the degree of polarized light rotation changes.
• At equilibrium 1/3 will be a and 2/3 will be ß
  anomer.

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MS/ Chiral carbon optic isomer number

• For each chiral center there are two optic
  isomers.
• They are not superimposable.
• The number of chiral carbon in
• Linear aldoses n N-2 so linear Glc has
  24 optic isomers
• Cyclic aldoses nN-1 so cyclic Glc has
  25 optic isomers
• Linear ketoses n N-3 so linear Fru has
  23 optic isomers
• Cyclic ketoses n N-2 so cyclic Fru has
  24 optic isomers

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Isomers
Steroisomers Same atom
connectivity different arrangement in pace
Functional Isomers different atom
connectivity
Aldose
Ketose
Conformational
Configurational
Boat
Chair
Envelop
Ring
OPTIC
Furan
Pyran
Diasteromers are not mirror image (epimers)
Anomers
Enantiomers are mirror
image
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MS/Different reactions

• Oxidation
• Reduction
• Ester formation
• Amination
• Glycoside formation

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MS/ Reactions/Oxidation

• 1 Aldonic acid Oxidation of aldehyde
• Group.Example Gluconic acid.

2 Uronic acid Oxidation of primary alcohol
group. Example glucoronic acid.
3 Aldaric acid Oxidation of aldehyde and
primary alcohol group Example Glucaric acid (
saccharic acid), Mannaric acid ( arabic
gum) Galactaric acid (mucic acid)
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MS/ Reactions/Oxidation

• 4 Furfural formation
• Oxidation and dehydration of M.S by very strong
  acids
• Example Furfural from pentoses and
  hydroxymethyl furfural from hexoses

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MS/ Reactions/ Reduction

• 1-Polyalcohols
• Reduction by gaining hydrogen
• Example Sorbitol from glucose,
• fructose and mannose
• 2- Deoxysugars
• Reduction by losing oxygen deoxysugar
  formation
• Example
• Deoxyribose form ribose,
• Fucose from L-galactose

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Examples of Polyalcohols
Examples of Deoxysugars
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MS/ Reactions/ Amination

• Amino sugars Glucosamine, mannosamine
• N- acetyl amino sugars N- acetyl
  glucosamine, N- acetyl mannosamine
• Sialic acids NAM PA

Glc A Man A Gal A NAG
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MS/ Reactions/ Ester formation

• Phosphate esters have an important role in
  metabolism.
• Example G6P, G1, 6 bis P, R5P.
• Sulfate esters of sugars are found in the
  glycosaminoglycanes (GAG).
• Example Gal 6 sulfate, Gal 4 sulfate.

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MS/ Reactions/ Glycoside formation

• O- glycoside compounds acetal or ketal are
  formed by combination of an alcohol ( a sugar or
  hydroxylic amino acids) with anomeric carbon of a
  sugar.
• Example oligo or polysaccharides.
• N- glycoside compounds they are formed by
  combination of nitrogen containing bases or
  amidic amino acids with anomeric carbon of a
  sugar.
• Example nucleosides.

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MS/ Reactions/ Glycoside formation
N- glycoside
O- glycoside
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Monosaccharide Derivatives

• Reducing sugars sugars with free anomeric
  carbons - they will reduce oxidizing agents, such
  as peroxide, ferricyanide and some metals (Cu and
  Ag)
• These redox reactions convert the sugar to a
  sugar acid
• Glucose is a reducing sugar - so these reactions
  are the basis for diagnostic tests for blood
  sugar

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Oligosaccharide
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Oligosaccharides

• Definition
• They are composed of 2-10 sugars.
• Disaccharides are most important
  oligosaccharides that are found in free form.
• Example Maltose, sucrose.
• Oligosaccharides with more than 2 residues
  usually are found as bound to the other
  compounds.
• Example glycoproteins or glycolipids.

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DS/ Reactions/ Glycoside formation
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DS formed by linkage of simple MS
a (D) glucopyranosyl 1, 2 fructofuranoside
ß (D) galactopyranosyl 1 4 glucopyranose
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DS/ Classification and nomenclature

• 1- Reducing disaccharides are formed by
  combination of anomeric carbon of one sugar with
  a hydroxyl group of another one. Because of one
  free anomeric carbon they are reducing. An yle
  suffix is added to the name of non-reducing
  residue.
• Example Maltose, lactose.
• 2-Non-reducing disaccharides are formed by
  combination of anomeric carbons of two sugars.
  Because there is no free anomeric carbon they are
  non-reducing. An yle suffix is added to the name
  of one and an ide suffix is added to the other
  one.
• Example Sucrose, Trehalose.