University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2022
Views:

310

Pages:

9
Author:

opendsniftiptfb

Section 8.5: Glycogen Metabolism §Glycogenesis §Synthesis of glycogen, the storage form of glucose, occurs after a meal ü Both synthesis & degradation controlled primarily by interplay between insulin and glucagon §Requires a set of three reactions (1 and 2 are preparatory and 3 is for chain elongation): 1. Synthesis of glucose-1-phosphate (G1P) from glucose6-phosphate by phosphoglucomutase 2. Synthesis of UDP-glucose from G1P by UDP-glucose phosphorylase Section 8.5: Glycogen Metabolism §Glycogenesis Continued 3. Synthesis of Glycogen from UDP-glucose requires two enzymes: § Glycogen synthase to grow the chain Figure 8.18 Glycogen Synthesis Section 8.5: Glycogen Metabolism Glycogenesis Continued § Branching enzyme amyloa(1,4à1,6)-glucosyl transferase creates a(1,6) linkages for branches Branching enzyme a(1,6) Glycosidic Linkage is formed Figure 8.18 Glycogen Synthesis Section 8.5: Glycogen Metabolism 1. Removal of glucose from nonreducing ends (glycogen phosphorylase) within four glucose of a branch point Figure 8.19 Glycogen Degradation Section 8.5: Glycogen Metabolism 2. Hydrolysis of the a(1,6) glycosidic bonds at branch points by amyloa(1,6)-glucosidase (debranching enzyme) Amylo-a(1,6)glucosidase Amylo-a(1,6)-glucosidase Figure 8.20 Glycogen Degradation via Debranching Enzyme Section 8.5: Glycogen Metabolism Regulation - Carefully regulated to maintain consistent energy levels §Controlled via insulin, glucagon, epinephrine, allosteric, effectors Glucagon – released from pancreas when blood glucose levels drop Figure 8.22 Major Factors Affecting Glycogen Metabolism ü Binds to receptor site on hepatocytes cell membrane ü Initiates signal transduction process ü Elevates cAMP, leads to glycogen phosphorylase activation ü Glucose released into bloodstream Cori’s disease - inherited defect, deficient in debranching enzyme ü Can store glycogen, cannot breakdown Section 8.5: Glycogen Metabolism §Glucagon activates glycogenolysis §Epinephrine release activates glycogenolysis; inhibits glycogenesis §Insulin inhibits glycogenolysis; activates glycogenesis Figure 8.22 Major Factors Affecting Glycogen Metabolism Biochemistry in Perspective §Saccharomyces cerevisiae and the Crabtree effect §S. cerevisiae is the only yeast that can produce ethanol and CO2 in such large quantities §S. cerevisiae ferments carbohydrates efficiently and dominates its environment due to the Crabtree effect §Unlike most fermenting organisms S. cerevisiae can also ferment sugar in the presence of O2 §As glucose and/or fructose levels rise pyruvate is diverted away from the citric acid cycle into ethanol synthesis §The Crabtree Effect §The phenomenon, in which glucose represses aerobic metabolism §Rapid production of ethanol has the effect of eliminating microbial competitors §Once glucose levels are depleted and O2 is available the yeast reabsorbs the ethanol and converts it to acetaldehyde for use as an energy source Biochemistry in Perspective Figure 8A Ethanol Metabolism in S. cerevisiae