Glycogen, Gluconeogenesis, and the Hexose Monophosphate Shunt Flashcards
Glycogen core protein
Glycogenin
Activated form of glucose that is ready for addition to the glycogen chain
UDP-glucose (G6P to G1P to UDP-glucose)
Rate limiting enzyme of glycogen synthesis
Glycogen synthase (alpha-1,4)
Activator of Glycogen synthase
Insulin
Inhibitors of Glycogen synthase
Glucagon (only in the liver), Epinephrine
Another name for the Branching Enzyme
Glycosyl alpha-1,4:alpha-1,6 Transferase
Rate limiting enzyme in Glycogenolysis
Glycogen phosphorylase (G-6-P to free Glucose)
Activators of Glycogen phosphorylase
Liver: Epinephrine, Glucagon; Skeletal Muscle: Epinephrine, AMP, Ca (high AMP and Ca signals an active muscle contraction and tells the muscle that it needs energy)
Inhibitors of Glycogen phosphorylase
Liver: Insulin; Skeletal Muscle: Insulin, ATP (presence of ATP tells the muscle to stop breaking down glycogen because there’s energy already)
Enzyme capable of hydrolyzing alpha-1,6-glycosidic bonds
Debranching enzyme (glucosyl alpha-1,4:alpha-1,4 transferase and alpha-1,6 glucosidase)
Severe hypoglycemia, lactic acidosis, hepatomegaly, hyperlipidemia, hyperuricemia, short stature doll-like facies, protruding abdomen, emaciated extremities
Von Gierke (Type I) disease; Substitution of galactose or fructose, or administration of glucagon or epinephrine won’t help.
Deficient enzyme in Von Gierke Disease
Glucose-6-phosphatase (sequesters free glucose from G-6-P)
Deficiency in Branching enzyme. Also called Amylopectinosis.
Andersen Disease, Type IV (Infantile hypotonia, cirrhosis, death by 2 years)
Deficient enzyme in McArdle Disease (Muscle cramps, weakness on exercise, myoglobinuria)
Muscle glycogen phosphorylase/Myophosphorylase (breaks alpha-1,4 glycosidic bonds to free up the G-1-Ps); Drinking sucrose-containing drink will help (provision of dietary glucose)
Type III Glycogen storage disease
Cori Disease (Mild hypoglycemia, liver enlargement due to Debranching Enzyme deficiency). Hypoglycemia is mild only because they can still get glucose from straight chains.
Deficiency in Hepatic Glycogen phosphorylase
Hers Disease, Type VI (Mild fasting hypoglycemia, hepatomegaly, cirrhosis). Hypoglycemia is mild because liver is capable of gluconeogenesis plus they can still get glucose from the muscle, but the liver is crowded by unutilized glycogen.
Massive cardiomegaly, muscle weakness, death by 2 years, deficiency in Lysosomal alpha-1,4-glucosidase (aka acid maltase)
Pompe Disease; Glycogen-like inclusion bodies (prominent lysosomes with clusters of electron-dense granules).
Substrates for gluconeogenesis
G3P (from TAGs in adipose), lactate, amino acids (gluconeogenic) from muscle protein
Ketogenic amino acids
Leucine and lysine
Amino acids that are both ketogenic and glucogenic
Phe Ile Trp Tyr Thr (PutangIna may tatlong Tite = PI! TTT!)
Major gluconeogenic amino acid in the body
Alanine (converted to pyruvate by ALTs, also the enzyme tested to assess hepatocyte damage)
Mitochondrial enzyme that converts Pyruvate to OAA
Pyruvate carboxylase (carboxylase enzymes require Biotin)
Deficiency in this vitamin, usually caused by ingestion of raw egg whites (avidin) and long-term home TPN
Biotin Deficiency (alopecia, scaly dermatitis, waxy pallor, and mild acidosis)
After shuttling OAA from the mitochondria to cytoplasm via the Malate shuttle, OAA is converted to PEP by
PEP Carboxykinase (PEPCK)
Hormones that induce PEPCK
Glucagon, Cortisol
Rate limiting enzyme in Gluconeogenesis, which is the arch nemesis of PFK (the rate-limiting enzyme in Glycolysis)
Fructose-1,6-bisphosphatase. It is activated by ATP, and inhibited by AMP and F-2,6-BP (Recall that F-2,6-BP is increased by Insulin and decreased by Glucagon)
Location of Glucose-6-phophatase
Lumen of the endoplasmic reticulum of LIVER
Gluconeogenesis is dependent on this metabolic pathway (because this pathway provides ATP consumed in gluconeogenesis)
Beta-oxidation of fatty acids
The two major mitochondrial enzymes that use pyruvate (one is catabolic, one is anabolic)
Pyruvate dehydrogenase and pyruvate carboylase (biotin). BOTH are regulated by the amount of Acetyl CoA
Cori cycle is
Lactate from RBC/exercising muscle is converted in the liver to Glucose, and this Glucose is returned back to RBC/muscle for consumption
Alanine cycle is
Alanine released from muscle is used for gluconeogenesis (pyruvate) and urea synthesis (amino group)
High NADH environment caused by Alcoholism favors formation of
Lactate (from pyruvate), Malate (from OAA), and G3P (from DHAP)
Metabolism of alcohol to acetate yields how many NADH
2 (one from alcohol DH and another from acetaldehyde DH)
Pathogenesis of alcoholic fatty liver
High NADH > very slow beta-oxidation despite hypoglycemia > FFAs continually released from adipose for supposed gluconeogenesis in liver > due to slow beta-ox, accumulation of FFAs in the liver instead > Presence of High G3P (High NADH favors conversion of DHAP to G3P) binds to the accumulated FFAs = triglycerides inappropriately formed in liver
Two major functions of Hexose Monophosphate Shunt/Pentose Phosphate Pathway
NADPH production (for oxidative burst), and Ribose-5-P production (for nucleotide synthesis)
Rate-limiting enzyme in PPP/HMS
G-6-P Dehydrogenase (G6P to 6-Phosphogluconate), induced by Insulin
The only Thiamine enzyme in RBCs, responsible for interconversion of the pentoses in PPP
Transketolase
Substrate responsible for maintaining a supply of reduced Glutathione; reduces oxidized glutathione via Glutathione Reductase
NADPH
Heinz bodies result from
Hemoglobin denaturation (due to peroxide accumulation in G6PD)
G6PD patients are not susceptible against what parasite/disease (believed to be an evolutionary adaptation in endemic countries)
Plasmodium / Malaria
Genetic deficiency in NADPH oxidase in the PMNs. Negative nitroblue tetrazolium test.
Chronic granulomatous disease (CGD), susceptibility to catalase-positive organisms, S. aureus, Kleb, E.coli, Candida, Aspergillus
Glycogenolysis happens in the
Cytoplasm
Most common genetic cause of hemolytic anemia
G6PD Deficiency
