Overview Structure glycogen polymer of glucose straight chain with α-1,4-bond branches with α-1,6-bond glycogen granule core glycogenin Function energy reserves that can provide glucose during a fast or ↑ energy demand supplies exhausted in < 24 hrs stored mainly in the liver and muscle muscle does not have glucose-6-phosphatase so it cannot release free glucose stores for its own consumption liver does have glucose-6-phosphatase so it can release free glucose can use supplies to maintain blood glucose levels Glycogenesis Glycogen synthesis Pathway glucose-6-phosphate converted to glucose-1-phosphate UDP group added to form UDP-glucose UDP-glucose added to polymer in an α-1,4 linkage catalyzed by glycogen synthase rate limiting step of glycogen synthesis polymer rearranged to create α-1,6 linked branches catalyzed by branching enzyme deficiency = Anderson disease Regulation glycogen synthase in liver activated by insulin inhibited by glucagon, epinephrine in muscle activated by insulin inhibited by epinephrine Glycogenolysis Glycogen catabolism Pathway glucose-glucose bond broken by addition of a phosphate catalyzed by glycogen phosphorylase rate limiting step of glycogenolysis hepatic deficiency = Hers disease (type VI) muscle deficiency = McArdle disease (type V) glucose-1-phosphate freed converted to glucose-6-phosphate debranching enzymes removes α-1,6 linked branches deficiency = Cori's disease (type III) liver converts glucose-6-phosphate to glucose catalyzed by glucose-6-phosphatase deficiency = von Gierke disease (type I) muscle puts glucose-6-phosphate into glycolysis Regulation glycogen phosphorylase in liver activated by epinephrine, glucagon via cAMP/protein kinase A inhibited by insulin remember: exact opposite of glycogen synthase hepatic glycogen regulatory processes both turn on forward direction and turn off reverse in skeletal muscle activated by epinephrine, AMP, Ca2+ inhibited by insulin, ATP remember: since muscular glycogen can only supply itself, it is regulated by its own energy supply (AMP/ATP ratio); while liver must supply energy to many other tissues, it functions independently of AMP/ATP ratio in hepatocytes Glycogen Storage Diseases (Glycogenolyses) Overview all disorders have abnormal glycogen metabolism leads to an accumulation of glycogen within cells organ dysfunction remember: disorders numbered in order of pathway from end (glucose release) to beginning (breakdown of glycogen polymer) Glucose release Type I: von Gierke lacks glucose-6-phosphatase presentation liver cannot release stored glucose hepatomegaly severe hypoglycemia body must rely on fat/protein catabolism for energy hyperlipidemia hyperuricemia lactic acidosis normal glycogen structure tests stimulation test with glucagon, fructose, galactose does not ↑ serum glucose Lysosomal pathway Type II: Pompe "trashes the Pump (heart)" lacks lysosomal α1,4-glucosidase degrades glycogen-resembling material in endosomes presentation buildup of glycogen in cardiac muscle electron dense granules inside lysosomes cardiomegaly hypertrophic cardiomyopathy Branching/debranching Type III: Cori lacks debranching enzyme remember: Cori = can't Catabolize branches 6-pack core - alpha 1,6 glucosidase defective presentation liver cannot break down glycogen past a branch point hepatomegaly hypoglycemia abnormal glycogen structure short outer glycogen chains Type IV: Anderson lacks branching enzyme remember: Anderson = can't Add branches presentation liver cannot form branched glycogen granules hypotonia cirrhosis Phosphorylase Type V: McArdles lacks muscle phosphorylase remember: McArdles = Muscle can't breakdown glycogen to glucose-1-phosphate accumulation of glycogen in muscle tissue presentation muscle weakness/cramps upon exertion myoglobinuria normal glycogen structure Type VI: Hers lacks hepatic phosphorylase remember: Hers = Hepatic presentation hepatomegaly fasting hypoglycemia can be mild due to gluconeogenic compensation
QUESTIONS 1 of 9 1 2 3 4 5 6 7 8 9 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.BC.15.74) You are presented with an infant boy who has repeatedly experienced hypoglycemia and seizures. On your exam, you note decreased muscle tone, growth retardation, and hepatomegaly. The patient has normal serum lactate. You review results of a liver biopsy, shown in Figure A. Further biochemical testing reveals abundant glycogen with abnormally short outer chains. Which of the following enzymes is most likely deficient in this patient? QID: 106621 FIGURES: A Type & Select Correct Answer 1 Muscle glycogen phosphorylase 6% (28/451) 2 Alpha-1,6-glucosidase 52% (234/451) 3 Glucose-6-phosphatase 12% (53/451) 4 Acid maltase 1% (6/451) 5 Branching enzyme 27% (121/451) M 1 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (M1.BC.15.74) A 12-year-old male presents to the pediatrician after two days of tea-colored urine which appeared to coincide with the first day of junior high football. He explains that he refused to go back to practice because he was humiliated by the other players due to his quick and excessive fatigue after a set of drills accompanined by pain in his muscles. A blood test revealed elevated creatine kinase and myoglobulin levels. A muscle biopsy was performed revealing large glycogen deposits and an enzyme histochemistry showed a lack of myophosphorylase activity. Which of the following reactions is not occuring in this individuals? QID: 106612 Type & Select Correct Answer 1 Converting glucose-6-phosphate to glucose 5% (13/284) 2 Breaking down glycogen to glucose-1-phosphate 76% (216/284) 3 Cleaving alpha-1,6 glycosidic bonds from glycogen 13% (36/284) 4 Creating alpha-1,6 glycosidic bonds in glycogen 3% (8/284) 5 Converting galactose to galactose-1-phosphate 0% (1/284) M 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK
All Videos (3) Login to View Community Videos Login to View Community Videos Pompe Disease Nathan Liu Biochemistry - Glycogen D 7/23/2018 203 views 5.0 (1) Login to View Community Videos Login to View Community Videos Glycogenolysis Keshav Mudgal Biochemistry - Glycogen D 12/15/2015 94 views 5.0 (2) Login to View Community Videos Login to View Community Videos Glycogenesis Keshav Mudgal Biochemistry - Glycogen D 12/15/2015 64 views 4.0 (1) Biochemistry | Glycogen Biochemistry - Glycogen Listen Now 13:29 min 8/14/2021 101 plays 4.0 (2)