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Unformatted text preview: Glycogen Metabolism Jonathan Galazka 3‐9‐2009 Glycogen is a polymer of alpha(1‐‐‐>4) linked glucose, with occasional alpha(1‐‐‐‐>6) branchings. (page 64 in reader) Glycogen allows cells to store large amounts of glucose without affecting the osmotic pressure of the cell. Glycogen breakdown Glycogen is depolymerized to glucose 6‐phosphate by three enzymes: 1. Glycogen phosphorylase removes the terminal glucose from the non‐ reducing end of glycogen. It releases glucose 1‐phosphate. It stops when reaching the fourth residue from and alpha(1‐‐‐>6) branch point (page 67 of reader). 2. The Debranching enzyme transfers three glucose residues from the branch point to a nearby non‐reducing end, forming a new alpha(1‐‐‐>4) linkage. It then removes the glucose remaining at the branch point. 3. Phosphoglucomutase converts the glucose 1‐phosphate that is removed by glycogen phosphorylase into glucose 6‐phosphate, which can enter the glycolytic pathway. Glycogen synthesis Glycogen synthesis is catalyzed by Glycogen synthase, which appends glucose to the non‐reducing end of a glycogen chain using an alpha(1‐‐‐>4) linkage (page 70 in your reader). The glucose in this reaction comes from UDPglucose (page 69 in your reader). New glycogen branches are formed by the glycogen branching enzyme, which transfers the terminal 6‐7 glucose residues from a glycogen chain having at least 11 total residues, to a point more ‘interior’ on the same glycogen chain. Theses 6‐7 residues are attached with an alpha(1‐‐‐>6) glycosidic bond. (page 70 in reader) A protein called Glycogenin acts as the nucleus of a single glycogen particle. (page 70 in reader) Regulation of glycogen synthesis and breakdown The regulation of glycogen synthesis and breakdown is quite complicated. Read pages 602‐608 in your book. Look for future review sheets on bspace. Final targets of regulation: Glycogen synthase, Glycogen phosphorylase Signals: cAMP, Insulin, Glucagon, AMP, Ca++, Epinephrine, Glucose, Glucose 6‐phosphate Signalling molecules: PKA, PP1, CKII, GSK3, PKB ...
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This note was uploaded on 05/07/2009 for the course MCB 58168 taught by Professor Thorner during the Spring '09 term at University of California, Berkeley.
- Spring '09