BCH 261 Lecture Notes - Lecture 13: Thrombin, Selectin, Animism
7 Jun 2018
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Ryerson University – Winter 2018
BCH 261-011&071 Biochemistry -April 11th, 2018
BCH 261-011&071 Biochemistry -April 11th, 2018
Lecture: Glycobiology and Carbohydrates
Terminology for carbohydrate stereochemistry configuration isomers
Enantiomers
● Stereoisomers that are mirror images of each other that are non-superposable
Diastereomers
● Diastereomers are stereoisomers that are not related as object and mirror image and
are not enantiomers
Anomers
● A geometric variation found in at certain atoms in carbohydrate molecules
Epimer
● A stereoisomer that differs in configuration at any single stereogenic center
● Galactose is a c4 epimer of glucose
Disaccharide, oligosaccharides, polysaccharides
How are glycosidic bonds formed?
1,4 glycosidic bond bonds are formed due to condensation reactions between a hydroxyl
residue on carbon-1 and the anomeric carbon-4 on two monosaccharides
Page 2 of 10
Ryerson University – Winter 2018
BCH 261-011&071 Biochemistry -April 11th, 2018
What kind of chemical reaction is glycosylation?
Glycosidic bond
● Two monosaccharide can be joined via a glyosidic bond between an anomeric carbon
and any free hydroxyl group
Energy needed to drive glycosylation reactions
● Energetic unfavorable formation of glycosidic bond is driven by hydrolysis of 2
phosphate linkages in ATP
● Energy from ATP is captured in the sugar nucleotide donor
Examples of disaccharides
Reducing disaccharides: Maltose, Lactose
Non-reducing disaccharides: Sucrose, Trehalose
Page 3 of 10
Ryerson University – Winter 2018
BCH 261-011&071 Biochemistry -April 11th, 2018
Polysaccharides
Homopolysaccharides
● Only one monomer
● Storage of monomer: glycogen, starch
● Structural elements: cellulose, chitin
Heteropolysaccharides
● Two or more types of monomer
Polysaccharides do not have a defined molecular weight unlike proteins because they are not
template driven and have a wide range of different lengths
Glycogen
● Energy storage polysaccharide
● Branched homopolymer of glucose
● Glucose monomer for alpha 1-4 linked chains
● Alpha 1-6 branches
● Many non-reducing ends and one reducing end
● Functions as main storage polymer in animals
● Why? When insoluble it has no effect on osmolarity of the cell
Starch
● Mixture of 2 homopolymers of glucose
● Amylose is an unbranched polymer of alpha 1-4 linked residues connected to D-glucose
● Amylopectin is alpha 1-4 chains with alpha 1-6 branches
○ Molecular weight of amylopectin is ~200 million
○ Branches like glycogen but branch points with linkers occur every 24-30 residues
● Main storage homo-polysaccharide in plants
Document Summary
Stereoisomers that are mirror images of each other that are non-superposable. Diastereomers are stereoisomers that are not related as object and mirror image and are not enantiomers. A geometric variation found in at certain atoms in carbohydrate molecules. A stereoisomer that differs in configuration at any single stereogenic center. Galactose is a c4 epimer of glucose. 1,4 glycosidic bond bonds are formed due to condensation reactions between a hydroxyl residue on carbon-1 and the anomeric carbon-4 on two monosaccharides. Two monosaccharide can be joined via a glyosidic bond between an anomeric carbon and any free hydroxyl group. Energetic unfavorable formation of glycosidic bond is driven by hydrolysis of 2 phosphate linkages in atp. Energy from atp is captured in the sugar nucleotide donor. Polysaccharides do not have a defined molecular weight unlike proteins because they are not template driven and have a wide range of different lengths. Glucose monomer for alpha 1-4 linked chains.
