Carbohydrates and Carbohydrate metabolism (Chemistry of Carbohydrate )

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Carbohydrates and Carbohydrate metabolism
(Chemistry of Carbohydrate )

• Objective
• Understand classification and structure of
  carbohydrates
• Understand multistep sequences (pathways) for
  carbohydrates metabolism.
• Study the metabolic disorders in carbohydrates
  metabolism.

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Carbohydrates and Carbohydrate metabolism
(Chemistry of Carbohydrate )

• Carbohydrate They are polyhydroxy aldhydes or
  ketones or any substances derived from them.
  
  OR
• Compounds that contains at least 3 carbon atoms,
  a number of OH group, in addition to aldhyde or
  ketone
• Formula for simple is (CH2O)n .

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Carbohydrates

• Importance and distribution of CHO in animal and
  plant tissue
• Plants
• (a) Cellulose which form the frame work of the
  plant and has supporting action.
• (b) Starch Which is the stored form of CHO.

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Carbohydrates

• Classification of CHO
• (1) Monosaccharide They are the simplest units
  of CHO, cannot hydrolyzed to the simpler form.
• They can be classified according to either number
  of carbon atoms, or whether they contain aldhydes
  or ketons.

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Carbohydrates (Monosaccharide)

• (1) according to number of carbons
• TriosesEx.Glyceraldehydes (aldotriose) Ex.
  Dihydroxyacetone ( ketotrioses)
• Tetrosis Ex. Erythrose (aldotetrosis) Ex.
  Erythulose (ketotetrosis)
• PentosesEx. Ribose (aldopentosis) Ex.
  Ribulose (ketoopentosis)
• Hexoses glucose , fructose , galactose, mannose

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Carbohydrates (Monosaccharide), Stereoisomerism

• Asymetric carbon atom A carbon atom that
  attached to four different atoms or groups of
  atoms.
• Any substance containing asymetric carbon atom,
  it has two different optically active isomers.
• Isomers Compounds that have the same chemical
  formula but have different structure. Ex.
  Glucose, fructose, mannose, galactose.

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Monosaccharide, Stereoisomerism

• Epimers Compounds that have the same chemical
  formula but differ in configuration around one
  carbon atom. Ex. ( D. glucose, D galactose C-4
  not galactose and mannose)
• Enantiomers A special type of isomers is found
  in the pairs of structure that are mirror images
  of each other.( L. glucose, D. glucose)
• D.glyceraldhyde in which OH group attached to
  asymmetric C atom is towards the right.
• L.glyceraldhyde in which OH group attached to
  asymmetric C atom is towards the left.

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Chemistry of Carbohydrate
Stereochemical relations in carbohydrates were
explored by Emil Fischer, who also devised a way
to represent these molecules. ? Fischer projection
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Important Monosaccharides
D-Glucose
D-Galactose
D-Mannose
D-Fructose
If only one of several stereocentres in a
molecule is diferent, such isomers are epimers.
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Cyclization of monosaccharide

• The simple chain formula fails to explain the
  many reaction so,
• Less than 1 of each of monosaccharides are found
  in a ring form, in which the aldhyde or keton
  group has reacted with an alcohol group in the
  same sugar.
• Formation of the ring results in the creation of
  anomeric carbon atomat C-1 of an aldose and on
  C-2 of a ketose
• These structure are designated the a ß
  configuration of the sugar.
• If the remaining OH is on the right ? a- sugar
• If the remaining OH is on the left ? ß - sugar

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Cyclization of monosaccharide

• Mutarotation The cyclic a ß anomers of sugar
  are in the equilibrium with each other, and can
  be spontaneously inter-converted in a process
  called mutarotation.
• Representation of sugar conformation (1)Fisher
  projection. (2)Haworth
  projection

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Cyclization of monosaccharide
b
a
Fischerprojection
D-glucose open chain
D-glucose ring form
a-D-glucose Haworth projection
a-D-glucose Chair conformation
anomeric C
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Chemistry of Carbohydrate

• Reducing sugar If the O2 of anomeric C- atom is
  not attached to any other compound, that sugar is
  a reducing sugar
• A reducing sugar can react with the chemical
  reagent (Ex. Bendict solution fehling solution)
  and reduce the reactive compound, with the
  anomeric C- atom is oxidized.

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Important Monosaccharides
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Disaccharide polysaccharide

• Disaccharides These are formed by condensation
  of 2 molecules of monosaccharide by a glycosidic
  linkage.
• oligosaccharides contain from3 to about 12 of
  monosaccharide units.
• polysaccharides contain more than 12 of
  monosaccharide units.

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Disaccharides

Lactose
Gal-b-1-4-Glu
Maltose
Glu-a-1-4-Glu
Sucrose
Glu-a-1-b-1-Fru
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polysaccharide

• Starch It is the most important polysacharide.
  It is a polyglucose, a-1-4 linked. Ther are two
  main components
  amylose linear, ca. 500 20 000
  linked glucose units
  amylopectin branched
  through a-1-6 bonds every 25 AGU
• glycogen body polysachharide similar to
  amylopectin, higher branched
• Cellulose is composed of b-1-4 linked glucose
  units. This bond cannot be cleaved by our
  digestive enzymes. Important part of cell walls
  and dietary fibre.

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Polysaccharides Starch, glycogen
a-1-6 branch pointin glycogen
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Polysaccharides - Cellulose
Stability of cellulose is increased through
formation of crystalline regions with extensive
hydrogen bonding
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Complex carbohydrates

• CHO can also attached by glycosidic bonds to
  non-CHO structure (a glycone) (Ex. Purine and
  pyrimidine as in nucleic acids, aromatic ring as
  those found in steroid bilirubin, proteins as
  glycoproteins glycosaminoglycans, and lipids as
  in glycolipids) to form glycosides.
• O- and N- glycosides If the group on the non-CHO
  is an OH group, the structure is an O-
  glycosides, whereas If the group on the non-CHO
  is an NH2 group, the structure is an N-
  glycosides.

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The Aldoses C3 C6
CHO
E T
RAXL
All Altruists Gladly Make
Gum In Gallon
Tanks
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The Ketoses C3 C6
Related Aldose ending ulose
Related Aldose ending ulose
P F S T
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Glucose structure in solution
Pentoses and hexoses can adopt two ring
structures 5-membered (Furanoses, after furan),
and 6-membered (Pyranoses, after pyran). Glucose
is in equilibrium between two pyranose forms. At
equilibrium, there is ca.65 b-D-Glucopyranose,
ca. 35 a-D-Glucopyranose, and lt1 of the
open-chain form.
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Fructose structure in solution
Fructose adopts a furanose structure, preferring
the a-anomer.
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Other roles and modifications of carbohydrates
In addition to their role as fuel molecules,
carbohydrates are important molecules as -
building blocks of nucleic acids - antigens
(blood groups, cellular interaction through
glycosylated surface proteins) - glycosylation
of proteins ? quality control system for protein
folding - glycosylation also determines
functional properties of proteins - metabolic
intermediates and specialised molecules