BMB402.7 - Chapter 15: Principles of Metabolic Regulation:...

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Chapter 15: Principles of Metabolic Regulation: Glucose and Glycogen January 31 2011
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Sugar Nucleotides Substrates for polymerization of monosaccharides into disaccharides, glycogen, starch, cellulose and extracellular polysaccharides Properties of sugar nucleotides: – Their formation is metabolically irreversable – Nucleotide moiety has many groups that can undergo noncovalent interactions with enzymes – Nucleotidyl group is an excellent leaving group – Tagged hexoses with nucleotidyl groups can be set aside for one purpose only
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Glycogen Synthesis UDP-glucose is the immediate donor of glucose residues in the reaction catalyzed by glycogen synthase Glycogen synthase catalyzes formation of ( α 1 Æ 4) glycosidic bonds in glycogen Glycogen synthase cannot make the ( α 1 Æ 6) bonds found at the branch points of glycogen
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Branch Synthesis in Glycogen Glycogen is a branched polymer of glucose units. The branches arise from ( α 1 Æ 6) linkages which occur every 8 to 12 residues. Glycogen branching enzyme = glycosyl ( α 4 Æ 6) transferase or amylo ( α 1 Æ 4) to ( α 1 Æ 6) transglycosylase. Branching is important to make glycogen more soluble and to increase the number of sites accessible to non-reducing ends.
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Glycogenin Structure Tyr 194 Asp 162 The very large glycogen polymer is built around glycogenin protein core. The first glucose residue is covalently joined to the protein glycogenin via an acetal linkage to a tyrosine–OH group on the protein.
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Glycogenin Catalyzes two Distinct Reactions After the glycogenin reactions, sugar units are added to the glycogen polymer by the action of glycogen synthase. The reaction involves transfer of a glucosyl unit from UDP-glucose to the C-4 hydroxyl group at a non-reducing end of a glycogen strand.
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Coordinated Regulation of Glycogen Breakdown and Synthesis Synthesis and degradation of glycogen must be carefully controlled so that this important energy reservoir can properly serve the metabolic needs of the organism.
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BMB402.7 - Chapter 15: Principles of Metabolic Regulation:...

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