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36 Cards in this Set
- Front
- Back
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What is gluconeogenesis and where does it occur?
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"formation of new sugar"
synthesis of glucose from noncarbohydrate predursors -occurs in the liver and a little in kidneys |
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What noncarbohydrate precursors can be converted into glucose?
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-lactate and pyruvate from glycolysis
-Krebs cycle intermediates -carbon skeletons of most amino acids |
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What are the 4 main fxns of gluconeogenesis?
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-provide glucose when diet intake is insufficient
-regulate acid balance - e.g. lactate disposed in Cori Cycle -Maintain amino acid balance -provide biosynthetic precursors for glycoproteins, glycolipids, and structural carbs |
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In step one of gluconeogenesis, what are the two enzymes to convert pyruvate to oxaloacetate and then to Phosphoenolpyruvate, where does it take place and how much energy is expended?
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-pyruvate carboxylase - only in mitochondria - uses 1 ATP per pyruvate molecule
-phosphenolpyruvate carboxykinase - in mitochondria or cytosol - uses 1 GTP per pyruvate molecule |
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After pyruvate is converted into oxaloacetate, what is it transported out of the mitochondria as?
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malate of aspartate
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In step 8 of gluconeogenesis, what is the enzyme responsible for hydrolyzing fructose-1,6-bisphophate to Fructose 6-phosphate and do you gain or use energy?
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Fructose-1,6-bisphosphatase
ATP is not used/gained, you regenerate a Pi. |
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In step 10 of gluconeogenesis, what enzyme is responsible for hydrolyzing Glucose-6-phosphatase to Glucose and do you gain or use energy?
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Glucose-6-phosphatase
ATP is not used/gained, you regenerate a Pi. |
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What are the enzymes used in the 7 reversible steps of gluconeogenesis?
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The same as in glycolysis
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What is the main storage form of glucose and where are the main places it is stored?
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glycogen
-Muscle - stored in cytosol and ER as granules (beta-particles) 1% muscle weight, 2x amount of liver glycogen -Liver - stored as alpha-particles (larger, rosette-shaped), 4-7% liver weight ---Liver stores enough glycogen for brain for half a day |
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How much ATP is expended in gluconeogenesis?
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6 ATP
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The glycogen containing granules also hold other molecules, what are they?
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-enzymes - catalyze glycogen synthesis and degradation
-proteins - regulate enzymatic processes |
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How is muscle glycogen utilized?
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serves as fuel reserve for the synthesis of ATP within that tissue
-exercise triggers mobilization of muscle glycogen for formation of ATP |
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How is liver glycogen utilized?
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functions as a glucose reserve for the maintenance of blood glucose concentrations
-liver glycogen levels vary greatly in response to intake of food |
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What is the structure of glycogen and what are its benefits?
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Highly branched which allows for simultaneous release of the glucose units at the end of every branch - IS QUICK!
alpha-1,4 glycosidic linkages - provide the straight chains alpha-1,6 glycosidic linkages - provide the branch points reducing end (not attacked) and non-reducing end (enzymes attack here) |
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What is glycogenolysis?
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the breakdown of glycogen to glucose or glucose-6-phosphate
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What is glycogenesis?
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Synthesis of glycogen from glucose
-McArdle's disease - can't break down muscle glycogen |
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Are glycogenolysis and glycogenesis the reverse rxns like glycolysis and glucloneogenesis?
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NO - they actually only have one enzyme in common.
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What are the 4 enzymes required for glycogenolysis?
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- glycogen debranching enzyme
-glycogen phosphorylase -phosphoglucomutase -glucose 6-phophatase (only used in liver glycogenolysis) |
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What is the 1st rxn of glycogenolysis, the enzyme, any energy required, and where does it take place?
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Glycogen phosphorylase - no energy involved
Glycogen (n-residues) + Pi <--> Glucose-1-phosphate (G1P) + glycogen (n1-residues) -occures at one of the many terminal, nonreducing ends of a glycogen molecule |
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What is the 2nd rxn of glycogenolysis, the enzyme, any energy required, and where does it take place?
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Phosphoglucomutase - no energy involved
-Glucose-1-phosphate <--> Glucose-6-phophate |
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What is the 3rd reaction and enzyme of glycogenolysis if you are in the liver?
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Glucose-6-phosphatase - hydrolysis - no energy required
Glucose-6-phospate + H2O <--> glucose + Pi Glucose is no available for use or put into blood stream |
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What is the 4th reaction and enzyme of glycogenolysis?
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Glycogen debranching enzyme - glycogen phosphorylase is specifec for alpha-1,4-glycosidic linkages so it gets stopped when it runs into alpha-1,6-glycosidic linkages.
--glycogen debranching enzyme takes a hatchet to it. -going on when needed, not necessarily in any order w/ the other enzymes |
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How does glycogen debranching enzyme work?
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-transfers a trisaccaharide unit from a limit branch of glycogen to the nonreducing end of another branch
-the remaining glycosol residue in the branch is hydrolyzed to yield glucose and debranched oxygen |
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Why does muscle tissue not convert glucose-6-phophate into glucose?
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muscle and other tissues lack the enzyme glucose-6-phosphatase
--muscle has G6P enter into glycolysis at the 2nd step |
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What is the 1st reaction and enzyme in glycogen synthesis?
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-glucokinase - liver
-hexokinase - other tissue Glucose +ATP -->glucose-6-phosphate + ADP |
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What is the 2nd rxn and enzyme in glycogen synthesis?
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phophoglucomutase - only enzyme that is in glycogenolysis also
Glucose-6-phosphate <--> glucose-1-phosphate |
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What is the 3rd rxn and enzyme in glycogen synthesis?
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UDP-Glucose Pyrophosphorylase
Glucose-1-phosphate + UTP --> UDP-glucose +PPi H2O + UTP --> 2Pi the 2nd rxn makes this total rxn nonreversible |
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What is the 4th rxn and enzyme in glycogen synthesis?
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Glycogen synthase - adds glucose to non-reducing ends of glycogen
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What is the 5th rxn and enzyme in glycogen synthesis?
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Branching enzyme - adds the alpha-1,6-glycosidic bonds to the glycogen
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What is the price of glycogen synthesis?
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1 molecule of UTP
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What conditions favor Glycogenolysis?
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High Demand for ATP (low ATP, G6P, high AMP)
-glycogen phophorylase is stimulated -glycogen synthase inhibited |
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What conditions favor Glycogen synthesis?
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Low Demand for ATP (high ATP, G6P)
-glycogen phophorylase is inhibited -glycogen synthase activated |
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Glycogen phosphorylase has an active and inactive/very little activity form (a and b). What enzymes make the switch?
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its a covalent modification by adding or removing a Pi (requires ATP to activate)
-protein kinase A activates phosphorylase kinase ---uses ATP to add a P -activated phosphorylase kinase activates glycogen phosphorylase ---uses ATP to add a P -phosphoprotein phosphatase-1 hydrolyzes both glycogen phosphorylase and phosphorylase kinase to deactivate them |
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What activates Protien Kinase A (PKA)
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cAMP - made from ATPs and breaks down to AMPs
[cAMP] determins the fraction of PKA in its active form and the rate at which it phosphorylates its substrates |
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What do Insulin and Glucagon do?
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Increased blood [glucose] --> INSULIN --> cAMP decreases --> activates Glycogen synthase --> Glycogen synthesis (storage)
Decreased blood [glucose] --> GLUCAGON --> cAMP increases --> activates glycogen phosphorylase --> Glycogenolysis (glycogen breakdown) -both made in pancreas |
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At what concentration is glucagon released?
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<5mM - during exercise, or several hrs after a meal is digested
-glucagon is critical for the liver's fxn in supplying glucose to tissue that depend primarily on glycolysis for their energy needs. -muscle cells don't respond to glucogon b/c they lack the appropriate receptor. |
