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45 Cards in this Set
- Front
- Back
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GLUT 2 |
- low affinity transporter in hepatocytes and pancreatic cells - captures excess glucose primarily for storage - Km = 15 mM - liver picks up excess glucose and will store it when glucose levels are high - in β- islet cells of the pancreas, GLUT 2 and glucokinase serve as the glucose sensor for insulin release |
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GLUT 4 |
- in adipose tissue and muscle - responds to glucose concentration in peripheral blood - rate of glucose transport is increased by insulin (stimulates movement of GLUT 4 transporters to the membrane) - Km = 5 mM therefore, transporter is saturated when BG levels are just a bit higher than normal |
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Adipose tissue |
- uses GLUT 4 receptors - glucose forms into dihydroxyacetone phosphate (DHAP) to convert into glycerol phosphate to store incoming fatty acids as triacylglycerols |
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Muscles |
- uses GLUT 4 receptors - stores excess glucose as glycogen |
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Glycolysis |
- cytoplasmic pathway that converts glucose into 2 pyruvate molecules - releases little energy - has 2 phosphorylations and one oxydation rxn |
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hexokinase |
- converts glucose into glucose 6-phosphate - trapped inside the cell - used in the 1st step of glycolysis - low Km - inhibited by glucose 6 - phosphate |
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Glucokinase |
- found in liver (hepatocytes): induced by insulin - found in pancreatic β- islet cells - high Km |
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Phosphofructokinase-1 |
- "PFK-1" - rate-limiting enzyme - main control point in glycolysis - where fructose 6-phosphateis phosphorylated to fructose 1,6 bisphosphate by using ATP - inhibited by ATP, citrate, and glucagon (hepatocytes) - activated by AMP and insulin (hepatocytes) |
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Phosphofructokinase -2 (PFK-2) |
-converts fructose 6- phosphate to fructose 2,6-biphosphate which activates PFK 1 - inhibited by glucagon - found mostly in the liver |
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glyceraldehyde-3-Phosphate Dehydrogenase |
- catalyzes oxidation and addition of inorganic phosphate to its substrate glyceraldehyde 3- phosphate - produces 1,3-biphosphoglycerate - reduces NAD+ to NADH |
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NADH |
- aerobic: oxidized my mitochondrial electron transport chain and provides energy for ATP synthesis by oxidative phosphorylation - anaerobic: oxidized to NAD+ - important function: energy carraige |
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3- Phosphoglycerate Kinase |
- transfers high energy phosphate from 1,3 bisphosphoglycerate to ADP to form ATP and 3- phosphoglycerate |
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substrate level phosphorylation |
- ADP phosphorylated to ATP using high energy intermediates - not dependent on oxygen - only means of ATP generation in aerobic tissue |
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Pyruvate Kinase |
- used in aerobic glycolysis - catalyzes substrate level phosphorylation of ADP by using phosphoenolpyruvate (PEP) - activated by fructose 1,6-biphosphate from PFK-1 rxn - uses feed-forward activation |
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feed forward activation |
- product of an earlier glycolysis rxn stimulates a later rxn in glycolysis |
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fermantation |
- occurs in the absence of oxygen - key enzyme: lactate dehydrogenase |
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lactate dehydrogenase |
- oxydizes NADH to NAD+ - to replenish the oxidized coenzyme for glyceraldehyde-3-phosphate dehydrogenase - reduces pyruvate to lactate |
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yeast cells in anaerobic conditions |
- ferment by the conversion of pryruvate to ethanol and carbon dioxide - replensihes NAD+ |
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hydydroxyacetone phosphate (DHAP) |
- used in hepatic and adipose tissue for triacyglycerol synthesis - formed from fruct 1,6 BP - can be isomerized to glycerol 3-phosphate to be converted into glycerol (back bone) |
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1,3 - biphosphaoglycerate (1,3 BPG) phosphoenolpyruvate (PEP) |
- high energy intermediates used to generate ATP by substrace0level phosphorylation - ONLY ATP gained in anaerobic respiration |
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irreversible steps of glycolysis |
- glucokinase/ hexokinase - PFK -1 - Pyruvate kinase (How Glycolysis Pushes Forward the Process: Kinases) |
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biphosphoglycerate mutase |
- in red blood cells - produces 2,3-biphosphoglycerate (2,3-BPG) - 2,3 - BPG binds allosterically to the β-chains of hemoglobin A and decreases its affinity for oxygen |
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lactose |
- hydolyzed to galactose and glucose by lactase |
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galactose |
- reaches liver through hepatic portal vein - formed from lactose - in tissues, galactose is phosphorylated by galactokinase --> galactose 1-phosphate --> (galactose -1-phosphate uridyltransferase and empimerase) --> glucose 1-phosphate |
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epimerases |
- enzymes that catalyze the converson of one sugar epimer to another - diastomers that differ at 1 chiral carbon |
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Fructose |
- formed from sucrose and absorbed in the hepatic portal vein - Phosphorylated into fructose-1-phosphate by the liver using fructokinase to trap it into the cell - fructose 1- phosphate --> (aldolase B) --> glyceraldehyde and DHAP - smaller amounts are metabolized in renal proximal tubules |
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Pyruvate Dehydrogenase |
- aerobic glycolysis: enters mitochondria --> acetyl CoA --> enters citric acid cycle of ATP or fatty acids |
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pyruvate dehydrogenase complex (PDH) |
-irreversible -cannot be used to concert acetyl CoA to pyruvate or glucose - in liver: activated by insulin - in nervous system: not responsive to hormones - complex of enzymes carrying out multiple reactions in succession - inhibited by acetyl CoA - build up of Acetyl CoA --> gluconeogenesis |
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Glycogen |
- storage form of glucose - synthesis and degradation = liver and skeletal muscle - in cytoplasm as granules - in liver: source of glucose thats mobilized btwn meals to prevent low blood sugar - in muslce: stored as an nergy reserve for muscle contraction |
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starch |
- long alpha-linked chains of glucose in which plants store glucose |
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glycogenesis |
- synthesis of glycogen granules - begins with glycogenin - glucose addition to a granule: glucose 6-phosphate --> glucose 1-phosphate --> (uridine diphosphate)--> UDP- glucose and pyrophosphate (PPi) --> glycogen |
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glycogen synthase |
- rate limiting enzyme of glycogen synthesus and forms α- 1,4 glycosidic bond - stimulated by glucose 6-phosphate and insulin - inhibited by epinephrine and glucagon - helps UDP - glucose to form glycogen |
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Branching enzyme (Glycosyl α-1, 4:α-1, 6 Transferase) |
- responsible for introducing α-1,6 linked branches into the granule as it grows |
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glycogenolysis |
- process of breaking down glycogen by glycogen phosphorylase --> glucose 1-phosphate --> glucose 6-phosphate - breaks bonds using inorganic phosphate instead of water |
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glycogen phosphorylase |
- breaks α-1,4 glycosidic bonds, releasing glucose 1-phosphate from the periphery of the granule - activated by glucagon in the liver - activated by AMP and epinephrine in the skeletal muscle |
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Debranching enzyme Glycosyl α-1,4:α1-,4 Transferanse α-1,6 Glucosidase |
- 2-enzyme complex that decontsructs the branches in glycogen that have been exposed by glycogen phosphorylase - breaks α-1,4 bond next to the branch point and moves smallglucose chain to the exposed end - forms new α-1,4 bond - hydolyzyes α-1,6 bond releasing the single residue a the branch point as free glucose (only free glucose) |
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isoforms |
- different version of the same protein |
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gluconeogenesis |
- how liver maintains BGL during fasting - promoted by glucagon and epi (higher BS) - inhibited by insulin (lower blood sugar) - Substrates: Glycerol 3-phosphate, Lactate, and glucogenic amino acids |
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glucogenic amino acids |
- can be converted into intermediates that feed into gluconeogenesis |
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ketogenic amino acids |
- converted into ketone bodies to be used as ana alternative fuel |
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important enzymes of gluconeigenesis |
-Pyruvate Carboxylase: activated by acetyl CoA from fatty acids - in mitorchondria - product = oxaloacetate (OAA) --> malate to leave mitochondria --> OAA in cytoplasm --> glucose production Phosphoenolpyruvate Carboxykinase (PEPCK): converts OAA --> PEP (requires GTP) - in cytoplasm - induced by glucagon and cortisol Fructose-1,6-Biphosphate: rate limiting step - in cytoplasm - reverses action of PFK-1by removing a phosphate from F-1,6-BP --> F-6-BP - activated by ATP - inhibited by AMP and F-2,6- BP Glucose-6-Phosphatase: found in the lumen of the ER in liver cells - used to collect glucokinase/hexokinase to convert glucose to glucose 6-phosphate **Phosphatases oppose kinases**
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Pentose Phosphate Pathway (PPP) |
- "hexose monophosphate shunt (HMP) - in cytoplasm - produces NADPH -source of ribose 5-phosphate for nucleotide synthesis |
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glucose 6 phosphate dehydrogenase (G6PD) |
- induced by insulin - inhibited by NAPH - activated by NAP+ - involved in the production of NAPH |
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NADPH |
- electron donor - reducing agent - protects cells from free radical oxidative damage caused by peroxides - involvement in biosynthesis of lipids and cholesterol - production of bactericidal bleach in lysosomes of WBC - maintenance of a supply of reduced glutathione |
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glutathoine |
- reducing agent that can help reverse radical formation before damage is done to the cell |
