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MCAT Bio. Chem Ch. 9
| Question | Answer |
|---|---|
| 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
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