510 likes | 751 Views
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
E N D
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 • Oxidation: energy-yielding pathway • Structural and protective elements • Lubricate skeletal joints • Recognition and adhesion between cells
Introduction (Continue) • Many, but not all, carbohydrates have the empirical formula (CH2O)n. • There are three major size classes of carbohydrates: • Monosaccharides • Oligosaccharides • Polysaccharides
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.
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.
Monosaccharides and Disacacharides • Monosaccharides are aldose or ketose
Monosaccharides and Disacacharides • Monosaccharides with three, four, five, six, and seven carbon atoms in their backbones: • Triose • Tetroses • Pentoses • Hexoses • Heptoses
Monosaccharides and Disacacharides • The hexoses are the most common monosaccharides in nature.
Monosaccharides and Disacacharides • All the monosaccharides except dihydroxyacetone contain one or more asymmetric carbon atoms.
Monosaccharides and Disacacharides • The simplest aldose, glyceraldehyde, contains one chiral center and therefore has two different optical isomers, or enantiomers.
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.
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.
Monosaccharides and Disacacharides • The formation of ring structures form: • Hemiacetals • hemiketals
Monosaccharides and Disacacharides • The αand βanomers of D-glucose interconvert in aqueous solution by a process called mutarotation.
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.
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.
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.
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-)
Hexose derivatives in organisms • Replacing the hydroxyl group with an amino group.
Hexose derivatives in organisms • Bacterial cell walls contain a derivative of glucosamine. OH OH
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.
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
Hexose derivatives in organisms • Monosaccharides can be oxidized by mild oxidizing agents such as ferric (Fe 3+) or cupric (Cu2+) ion.
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
Hexose derivatives in organisms • The acidic glucose derivatives are:
Hexose derivatives in organisms • In addition to previous mentioned acidic hexose derivatives, there is a nine-carbon acidic sugar:
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.
Hexose derivatives in organisms • In the synthesis and metabolism of carbohydrates, the intermediates are very often not the sugars themselves but their phosphorylated derivatives.
Disaccharides contain a glycosidic bond • Disaccharides consist of two monosaccharides joined covalently by an O-glycosidic bond.
Hexose derivatives in organisms • Nonreducing disaccharides are named as glycosides; in this case, the positions joined are the anomeric carbons.