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MCAT Bio. Chem Ch. 9

QuestionAnswer
GLUT 2 Found in the liver (for glucose storage) and pancreatic B-islet cells (as part of the glucose sensor). It has a high Km.
GLUT 4 Found in adipose tissue and muscle is stimulated by insulin. It has a low Km.
Glycolysis Occurs in the cytoplasm of all cells, and does not oxygen. It yields 2 ATP per molecule of glucose.
Glucokinase Converts glucose to glucose 6-phosphate. It is present in the pancreatic B-islet cells as part of the glucose sensor and is responsive to insulin in the liver.
Hexokinase Converts glucose to glucose 6-phosphate in peripheral tissues.
Phosphofructokinase-1 (PFK-1) Phosphorylates fructose 6-phosphate to fructose 1,6-biphosphate in the rate limiting step of glycolysis. PFK-1 is activated by AMP and fructose 2,6-bisphosphate (F2,6-BP) and is inhibited by ATP and citrate.
Phosphofructokinase-2 (PFK-2) Produces the F2,6-BP that activates PFK-1. It is activated by insulin and inhibited by glucagon.
Glyceraldehyde-3-phosphate dehydrogenase Produces NADH, which can feed into the electron transport chain.
3-phosphoglycerate kinase and pyruvate kinase Perform substrate-level phosphorylation, placing an inorganic phosphate (Pi) onto ADP to form ATP.
Glucokinase/hexokinase, PFK-1, and Pyruvate Kinase Enzymes that catalyze irreversible reactions
NADH Produced In Glycolysis: Oxidized by the mitochondrial electron transport chain when oxygen is present.
Lactate Dehydrogenase (cytoplasmic) Oxidizes NADH produced in Glycolysis if oxygen or mitochondria are absent. Ex's: RBC's, skeletal muscle during short intense bursts of exercise, and cells deprived of oxygen.
Galactose Comes from lactose in milk.
Galactokinase Traps lactose a cell.
Galactose-1-phosphate uridyltransferase + an epimerase Convert galactokinase to glucose 1-phosphate
Fructose Comes from honey, fruit, and sucrose.
Fructokinase Traps fructose in the cell.
Adolase B Cleaves fructose to form glyceraldehyde and DHAP.
Pyruvate Dehydrogenase Complex of enzymes that converts pyruvate to acetyl-CoA. It is stimulated by insulin and inhibited by acetyl-CoA.
Glycogenesis (Glycogen Synthesis) Production of glycogen using two main enzymes
Glycogen Synthase Creates alpha-1,4 glycosidic links between glucose molecules. It is activated by insulin in liver and muscle.
Branching Enzyme Moves a block of oligoglucose from one chain, and adds it to the growing glycogen as a new branch using alpha-1,6 glycosidic link.
Glycogenolysis Breakdown of glycogen using two main enzymes.
Glycogen Phosphorylase Removes single glucose 1-phosphate molecules by breaking alpha-1,4 glycosidic links.
How Glycogen Phosphorylase Is Activated In The Liver it is activated by glucagon to prevent low blood sugar
How Glycogen Phosphorylase Is Activated In Exercised Skelectal Muscle It is activated by epinephrine and AMP to provide glucose for the muscle itself.
Debranching Enzyme Moves a block of oligoglucose from one branch and connects it to the chain using an alpha-1,4 glycosidic link. It also removes the branchpoint, which is connected via an alpha-1,6 glycosidic link, releasing a free glucose molecule.
Gluconeogenesis Occurs in the cytoplasm and mitochondria, mostly in the liver. There is a small contribution from the kidneys. It is simply the reverse of glycolysis, and uses the same enzymes.
First Step Of Glycolysis: Pyruvate Carboxylase Converts pyruvate into oxaloacetate, which is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxylkinase (PEPCK).
First Step Of Glycolysis: Pyruvate Carboxylase Cont (PEPCK and Pyruvate Carboxylase) Together, these two enzymes bypass pyruvate kinase. Pyruvate carboyxlase is activated by acetyl-CoA from Beta-oxidation; PEPC is activated by glucagon and cortisol.
Fructose-1,6-bisphosphatase (Rate Limiting Step Of Gluconeogenesis) Converts fructose 1,6-bisphosphate to fructose 6-phosphate, bypassing phosphofructokinase-1. It is activated by ATP directly and glucagon indirectly via decreased levels of fructose 2,6-bisphosphate.
How Fructose-1,6-bisphosphatase Is Inhibited It is inhibited by AMP directly, and insulin indirectly via increased levels of fructose 2,6-bisphosphate
Glucose-6-phosphatase Converts glucose 6-phosphate to free glucose, bypassing glucokinase. IT is found only in the endoplasmic reticulum of the liver.
Pentose Phosphate Pathway (PPP) Also Know As The Hexose Monophosphate (HMP) Shunt Occurs in the cytoplasm of most cells, generating NADPH and sugars for biosynthesis (derived from ribulose 5-phosphate)
Glucose-6-phosphate dehydrogenase Rate limiting enzyme of the PPP, which is activated by NADP+ and inhibited by NADPH and insulin.
Created by: SamB91