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54 Cards in this Set
- Front
- Back
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Where does the liver store triacylgylcerol?
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It does not store triacylglycerol but it packages it into VLDL
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What is the limitation of storage for adipose tissue?
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It is limited mainly by the ability of the heart to pump blood through the capillaries of the expanding adipose mass
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When can we expect glucokinase to be the most active?
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Glucokinase has a high Km so it most active in the fed state.
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What is the function of glucokinase?
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It converts glucose to glucose-6-phosphate
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Insulin _____ glucokinase and glucagon _______ glucokinase
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induces
represses |
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What is the enzyme that is responsible for the conversion of glucose-6-phosphate to glycogen
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glycogen synthase
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What activates glycogen synthase?
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Elevated insulin levels; decreased glucagon levels; increased levels of glucose
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What are the key enzymes that regulate the conversion of glucose-6-phosphate to pyruvate?
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Phosophofructokinase -1
Pyruvate kinase |
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What is the activation pathway for phosphofructokinase -1 (PFK-1)?
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1. PFK-2 is dephosphorylated after a meal
2. PFK-2 produces fructose 2,6 biphosphate 3. fructose 2,6 biphosphate and AMP allosterically activated PFK-1 |
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What activates Pyruvate kinase?
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It is activated by dephosphorylation, which is stimulated by the increase of the insulin/glucagon ratio in the fed state
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What is the role of pyruvate dehydrogenase?
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It converts pyruvate to acetyl CoA
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Where can we find pyruvate dehydrogenase?
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It can only found in the mitochondria
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When is pyruvate dehydrogenase the most active?
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It is activated by insulin; with a high supply of substrates and ADP
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What is the enzyme that converts the reaction of pyruvate to oxaloacetate?
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Pyruvate carboxylase
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When is the puruvate carboxylase the most active?
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With elevated levels of acetyl CoA
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What is the transport mechanism for acetyl CoA?
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Acetyl CoA cannot cross the mitochondrial membrane so it has to condense with oxaloacetate to form citrate. Then the unneeded citrate crosses into the cytosol
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What conditions favor high citrate?
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A high ratio of NADH/NAD+ ratio in the mitchondria inhibits isocitrate dehydrogenase --> citrate accumulation in the mitchondrial matrix
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What is the fate of citrate in the cytosol?
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Citrate lyase acts on citrate to form oxaloacetate and acetyl CoA
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How is oxaloaceteate recycled in the cytoplasm?
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Oxaloacetate is recylced to pyruvate via cytsolic malate dehydrogenase and malic enyzme
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What is malic enzyme used for ?
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Malic enzyme is used to convert malate to pyruvate
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How is acetyl CoA converted to malonyl CoA?
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Acetyl CoA carboxylase catalyzes the conversion of acetyl CoA to malonyl CoA
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Why is malonyl CoA useful in the fatty acid complex?
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Malonyl CoA provides the two-carbon units for the synthesis of palmitate on the growing fatty acyl synthase complex
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How does insulin activate acetyl CoA carboxylase?
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A phosphatase activated by insulin activates the enzyme by phosphorylation.
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What regulates acetyl CoA carboxylase?
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It is activated by citrate ( causes the enzyme to polymerize), it is inhibited by long chain fatty acid acyl CoA; The quantity of the enzyme increases in the fed state.
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What is the role of carnitine:palmitoyltransferase I ?
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CPTI is the enzyme that prepares long chain fatty acyl CoA transport into mitochondria.
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In the fed state, when acetyl CoA carboxylase is active and malonyl CoA levels are ______, newly made fatty acids are converted to ______
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elevated
triacylgylcerols |
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What is the role of glucose-6-phosphate dehydrogenase?
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Glucose 6-dehydrogenase generates NADPH in the pentose phosphate pathway
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How is the fatty acid synthase complex affected by insulin?
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The gene that make this enzyme complex are made by increases in the insulin/glucagon ratio --> in the fed state the quantity of the fatty acid synthase increases
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What is the effects of insulin on malic enzyme and glucose 6- phosphate?
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Both are induced by insulin
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What is the fate of palmitate made by the synthase complex?
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The palmitate made by the synthase complex is converted to palmityl CoA and elongated and desaturated to make other fatty acyl CoA molecules --> converted to triacyglycerols
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Where is LPL found?
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In the endothelial cells of capillaries in muscle and adipose tissue
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What is the function of LPL?
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It hydrolyzes the triacylglycerols in chylomicrons and VLDL to fatty acids and glycerol
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The LPL found in muscle have a ____ Km but the LPL in the adipose ____Km
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low
high |
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When is the adipose LPL most active?
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It is most active after a meal when blood lipoprotein levels are elevated
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With low insulin levels, we can expect the hydrolysis of VLDL and chylomicrons to be ______.
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decreased
This results in hypertriglyceridemia |
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How do chylomicrons and VLDL recognized by LPL?
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Apoprotein CII, donated to chylomicrons and VLDL by HDL, activates LPL
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Why can't adipose tissue use the gylcerol released by LPL?
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They lack glycerol kinase
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Where does adipose tissue the glycerol for triacylglycerol synthesis?
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Glucose enters these cells and is oxidized and provides the glycerol 3-phosphate moitey for triacylglycerol synthesis
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Where do liver cells obtain glycerol for triacylglycerol synthesis?
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In the fed state, liver cells convert glycerol to the glycerol moiety of the triacyglycerols of VLDL
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How does glucagon inactivate glycogen synthase?
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Glucagon stimulates adenylate cyclase to make cAMP ==> activates protein kinase A.Protein kinase A phosphorylates and inactivates glycogen synthase
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What are the actions of Protein A in the liver cell?
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Protein kinase A phosphorylates phosphorylase kinase which phosphorylates and activates glycogen phosphorylase
It also phosphorylates and inactivates glycogen synthase |
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During fasting, the insulin/glucagon ratio ______.
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decreases
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What is the role of Glucose 6-phosphatase?
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It is a gluconeogenesis enzyme.
It converts glucose 6-phosphate to glucose |
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What is the role of Fructose 1,6 bisphosphatase?
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It is a gluconeogenesis enzyme.
It converts Fructose 1,6 biphosphatase to Fructose 6-phosphate |
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What is the role of Phosphoenolpyruvate carboxykinase?
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It is a gluconeogenesis enzyme
It converts oxaloacetate to PEP |
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What is responsible for the inactivation of pyruvate kinase?
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cAMP- mediated phosphorylation
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What is responsible for activating Fructose 1,6 biphosphatase?
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Fructose 1,6 biphosphatase is activated because the levels of its inhibitor are low
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How does glucagon stimulate increased enzyme synthesis of PEP carboxylase, Fructose 1,6 bisphosphatase, Glucose 6-phosphatase?
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Glucagon activates the cAMP- dependent protein kinase . cAMP dependent protein kinase activates and phosphorylates CREB ( cAMP response element binding protein)
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What is CREB?
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CREB ( cAMP response element binding protein) is a transcription factor . When it is activated enzymes are made
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During fasting, blood glucagon levels ____ and the level of cAMP ____ in adipose cells.
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rise
rises |
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How does insulin inhibit lipolysis in the adipocyte?
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Insulin normally inhibits lipolysis by decreasing the lipolytic activity of hormone-sensitive lipase in the adipocyte
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What is the function of hormone sensitive lipase?
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HSL cleaves fatty acids from triacylglycerols
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What activates hormone sensitive lipase?
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Activated Protein kinase A causes the phosphorylation of hormone sensitive lipase.
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Name some hormones that activate HSL.
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Epinephrine
ACTH Growth Hormone |
