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Isfahan University of Technology. Advance Biochemistry. Part 1: Carbohydrates Prepared by: Dr A. Riasi ( Isfahan University of Technology ) Reference: Lehninger Biochemistry. Introduction. Importance of carbohydrates: Photosynthesis Dietary staple: sugar and starch

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slide2

Isfahan University of Technology

Advance Biochemistry

Part 1:

Carbohydrates

Prepared by:

Dr A. Riasi ( Isfahan University of Technology)

Reference:

Lehninger Biochemistry

slide3

Introduction

  • Importance of carbohydrates:
    • Photosynthesis
    • Dietary staple: sugar and starch
    • Oxidation: energy-yielding pathway
    • Structural and protective elements
    • Lubricate skeletal joints
    • Recognition and adhesion between cells
slide4

Introduction (Continue)

  • Many, but not all, carbohydrates have the empirical formula (CH2O)n.
  • There are three major size classes of carbohydrates:
    • Monosaccharides
    • Oligosaccharides
    • Polysaccharides
slide6

Monosaccharides and Disacacharides

  • Monosaccharide characteristics:
    • Consist of a single polyhydroxy aldehyde or ketone unit.
    • Many of the carbon atoms to which hydroxyl groups are attached are chiral centers.
slide7

Monosaccharides and Disacacharides

  • Monosaccharides are colorless, crystalline solids.
  • In the open-chain form, one of the carbon atoms is double-bonded to an oxygen atom.
slide8

Monosaccharides and Disacacharides

  • Monosaccharides are aldose or ketose
slide9

Monosaccharides and Disacacharides

  • Monosaccharides with three, four, five, six, and seven carbon atoms in their backbones:
    • Triose
    • Tetroses
    • Pentoses
    • Hexoses
    • Heptoses
slide10

Monosaccharides and Disacacharides

  • The hexoses are the most common monosaccharides in nature.
slide12

Monosaccharides and Disacacharides

  • All the monosaccharides except dihydroxyacetone contain one or more asymmetric carbon atoms.
slide13

Monosaccharides and Disacacharides

  • The simplest aldose, glyceraldehyde, contains one chiral center and therefore has two different optical isomers, or enantiomers.
slide15

Monosaccharides and Disacacharides

  • In general, a molecule with n chiral centers can have 2nstereoisomers.
  • Glyceraldehyde has 21 = 2; the aldohexoses, with four chiral centers, have 24 = 16 stereoisomers.
slide23

Monosaccharides and Disacacharides

  • Some sugars occur naturally in their L form:
    • L-arabinose
    • L isomers of some sugar derivatives that are common components of glycoconjugates.
slide24

Monosaccharides and Disacacharides

  • The formation of ring structures form:
    • Hemiacetals
    • hemiketals
slide29

Monosaccharides and Disacacharides

  • The αand βanomers of D-glucose interconvert in aqueous solution by a process called mutarotation.
slide31

Monosaccharides and Disacacharides

  • Ketohexoses also occur in αand β anomeric forms.
  • D-Fructose readily forms the furanose ring the more common anomer of this sugar in combined forms or in derivatives is β-D-fructofuranose.
slide34

Monosaccharides and Disacacharides

  • Two conformationsof a molecule are interconvertible without the breakage of covalent bonds
  • Two configurationscan be interconverted only by breaking a covalent bond for example, in the case of αand βconfigurations, the bond involving the ring oxygen atom.
slide35

Hexose derivatives in organisms

  • There are a number of sugar derivatives in which a hydroxyl group in the parent compound is replaced with another substituent or the carbon atom is oxidized to a carboxyl group.
slide36

Hexose derivatives in organisms

  • Different derivatives of hexoses:
    • Containing an amine group (-NH2)
    • Containing a N-acetyl group (-NH-CO-CH3)
    • Containing an acid lactic and an amine group or a N-actyl group
    • Containing a methyl group (-CH3)
    • Containing a carboxyl group (-COO-)
slide37

Hexose derivatives in organisms

  • Replacing the hydroxyl group with an amino group.
slide38

Hexose derivatives in organisms

  • Bacterial cell walls contain a derivative of glucosamine.

OH

OH

slide39

Hexose derivatives in organisms

  • The substitution of a hydrogen hydroxyl group at C-6 of L-galactose or L-mannose produces L-fucose or L-rhamnose, respectively.
slide40

Hexose derivatives in organisms

  • Oxidation of the carbonyl (aldehyde) carbon of glucose, galactose, or mannose forms the corresponding aldonic acids:
    • Gluconic acid
    • Galactonic acid
    • Manonic acid
slide41

Hexose derivatives in organisms

  • Monosaccharides can be oxidized by mild oxidizing agents such as ferric (Fe 3+) or cupric (Cu2+) ion.
slide42

Hexose derivatives in organisms

  • Oxidation of the carbon at the other end of the carbon chain (C-6) of glucose, galactose, or mannose forms the corresponding uronic acid:
    • Glucuronic
    • Galacturonic
    • Mannuronic acid
slide43

Hexose derivatives in organisms

  • The acidic glucose derivatives are:
slide44

Hexose derivatives in organisms

  • In addition to previous mentioned acidic hexose derivatives, there is a nine-carbon acidic sugar:
slide45

Hexose derivatives in organisms

  • In bacterial systems an enzyme uses a mannose derivative as a substrate, inserting three carbons from pyruvate into the resulting sialic acid structure.
slide46

Hexose derivatives in organisms

  • In the synthesis and metabolism of carbohydrates, the intermediates are very often not the sugars themselves but their phosphorylated derivatives.
slide47

Disaccharides contain a glycosidic bond

  • Disaccharides consist of two monosaccharides joined covalently by an O-glycosidic bond.
slide49

Hexose derivatives in organisms

  • Nonreducing disaccharides are named as glycosides; in this case, the positions joined are the anomeric carbons.
slide51

Hexose derivatives in organisms

  • Trehalose, Glc(1 1)Glc is a disaccharide of D-glucose that, like sucrose, is a nonreducing sugar.
  • It is a major constituent of the circulating fluid (hemolymph) of insects, serving as an energy storage compound.
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