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29 Cards in this Set
- Front
- Back
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GLUT 2 |
found in the liver (for glucose storage) and pancreatic β-islet cells (as part of the glucose sensor which causes release of insulin) not responsive to insulin it has a high Km (15 mM) so it can't be saturated under normal physiological conditions |
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GLUT 4 |
found in adipose tissue and muscle and is stimulated by insulin its has low Km (5mM) so it is saturated when glucose levels are only slightly above 5 mM |
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glycolysis |
occurs in the cytoplasm of all cells, and does not require oxygen. It yields 2 ATP per molecule of glucose |
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important glycolytic enzymes include |
glucokinase hexokinase phosphofructokinase-1 (PFK-1) phosphofructokinase-2 (PFK-2) glyceraldehyde-3-phosphate dehydrogenase 3-phosphoglycerate kinase pyruvate kinase |
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glucokinase |
phosphorylates glucose to form glucose 6-phosphate, "trapping" glucose in liver and pancreas cells it is present in the pancreatic β-islet cells as part of the glucose sensor (along with GLUT 2) in liver cells, it is induced by insulin it is irreversible |
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hexokinase |
phosphorylates glucose to form glucose 6-phosphate in peripheral tissues, "trapping" glucose in the cell it is inhibited by glucose 6-phosphate it is irreversible |
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phosphofructokinase-1 (PFK-1) |
phosphorylates fructose 6-phosphate to fructose 1,6-biphosphate using ATP in the rate-limiting step of glycolysis activated by AMP,fructose 2,6-bisphosphate (F2,6-BP) and insulin it is inhibited by ATP, citrate and glucagon it is reversible |
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phosphofructokinase-2 (PFK-2) |
produces the F2,6-BP that activates PFK-1 it is activated by insulin and inhibited by glucagon |
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glyceraldehyde-3-phosphate dehydrogenase |
produces NADH (which can feed into the electron transport chain) while phosphorylating glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate it is reversible |
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3-phosphoglycerate kinase |
performs substrate-level phosphorylation, placing an inorganic phosphate (Pi) from 1,3-bisphosphoglycerate onto ADP to form ATP and 3-phosphoglycerate it is reversible |
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pyruvate kinase |
performs substrate-level phosphorylation, placing an inorganic phosphate (Pi) from phosphoenolpyruvate (PEP) onto ADP to form ATP and pyruvate it is activated by fructose 1,6-bisphosphate it is irreversible |
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the enzymes that catalyze irreversible reactions |
glucokinase/hexokinase PFK-1 pyruvate kinase |
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mitochondrial electron transport chain |
when oxygen is present, oxidizes the NADH produced in glycolysis
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cytoplasmic lactate dehydrogenase |
if oxygen or mitochondria are absent, oxidizes the NADH produced in glycolysis examples include: red blood cells skeletal muscle (during short, intense bursts of exercise) any cell deprived of oxygen |
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galactose |
comes from lactose in milk it is trapped (due to phosphorylation) in the cell by galactokinase it is converted to glucose 1-phosphate via galactose-1-phosphate uridyltransferase and an epimerase (this link galactose metabolism to glycolysis because the product can feed directly into glycolysis) |
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fructose |
comes from honey, fruit and sucrose (common table sugar) it is trapped in the cell (due to phosphorylation) by fructokinase (with a small contribution from hexokinase) and then cleaved by aldolase B to form glyceraldehyde (which can be phosphorylated to form glyceraldehyde 3-phosphate) and dihydroxyacetone (DHAP), which are glycolytic intermediates thus linking the pathways |
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pyruvate dehydrogenase (PDH) complex |
refers to a complex of enzymes that converts pyruvate to acetyl-CoA it is stimulated by insulin and inhibited by acetyl-CoA reactants: pyruvate NAD+ CoA products: acetyl-CoA NADH CO2 |
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glycogenesis |
glycose synthesis the production of glycogen using two main enzymes: glycogen synthase and branching enzyme |
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glycogen synthase |
creates α-1,4 glycosidic links between glucose molecules it is activated by insulin in liver and muscle |
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branching enzyme |
moves a block of oligoglucose from one chain and adds it to the growing glycogen as a new branch using an α-1,6 glycosidic link |
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glycogenolysis |
the breakdown of glycogen using two main enzymes: glycogen phosphorylase and debranching enzyme |
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glycogen phosphorylase |
removes single glucose 1-phosphate molecules by breaking α-1,4 glycosidic links in the liver, it is activated by glucagon to prevent low blood sugar in exercising skeletal muscle, it is activated by epinephrine and AMP to provide glucose for muscle itself |
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debranching enzyme |
moves a block of oligoglucose from one branch and connects it to the chain using an α-1,4 glycosidic link it also removes the branchpoint, which is connect via an α-1,6 glycosidic link, releasing a free glucose molecule |
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gluconeogenesis |
occurs in both the cytoplasm and mitochondria, predominantly in the liver there is a small contribution from the kidneys most is simply the reverse of glycolysis, using the same enzyme |
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pyruvate carboxylase |
converts pyruvate into oxaloacetate, which is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase (PEPCK) together, these two enzymes bypass pyruvate kinase pyruvate carboxylase is activated by acetyl-CoA from β-oxidation PEPCK is activated by glucagon and cortisol |
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fuctose-1,6-bisphosphatase |
converts fructose 1,6-bisphosphate to fructose 6-phosphate, bypassing phosphofructokinase-1 this is the rate limiting step of gluconeogenesis it is activated by ATP directly and glucagon indirectly (via decreased levels of fructose 2,6-bisphosphate) it is inhibited by AMP directly and insulin indirecly (via increased levels of fructose 2,6-bisphosphate) |
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glucose-6-phosphatase |
converts glucose 6-phosphate to free glucose, bypassing glucokinase it is found only in the endoplasmic reticulum of the liver |
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pentose phosphate pathway (PPP) |
also known as hexose monophosphate (HMP) shunt occurs in the cytoplasm of most cells, generating NADPH and sugars for biosynthesis (derived from ribulose 5-phosphate) |
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glucose-6-phosphate dehydrogenase |
the rate-limiting enzyme of the pentose phosphate pathway activated by NADP+ and inhibited by NADPH and insulin |
