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25 Cards in this Set
- Front
- Back
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What is steady state? |
Nonequilibrium state of the cell in which components of the system are maintained at fairly constant concentrations. Allows for the entry of materials that is balanced by the expulsion of waste preventing a net change in mass or gross composition of the system
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What is metabolic flux? |
Rate by which a metabolic pathway is utilized under cellular conditions.
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How do steady state and metabolic flux relate to one another? |
Metabolic flux will change as system changes to keep it at steady state. |
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What enzymes will be regulated? |
Those that catalyze irreversible reactions. |
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How does regulation of an irreversible enzyme lead to regulation of the entire pathway? |
Irreversible steps are the “rate-limiting” steps of the metabolic path whereas the reversible steps are rapid and respond solely to changes in the levels of their substrates and products.
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How do steady state and metabolic flux relate to control aspects of pathways? |
The rate at which materials are used and waste is generated will match the changing needs of the system.
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What is an allosteric enzyme? |
Enzymes that alternate between separate forms in response to modulator binding. The conformational change results in a form that is more or less active than the previous.
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How do allosteric enzyme kinetics compare to enzymes with hyperbolic curves? |
Allosteric enzyme kinetics display sigmoidal curves and cannot be described the Michealis-Mentin Equation. Both display saturation behavior. |
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What is the K0.5? |
The amount of substrate required to reach 1/2 Vmax for allosteric/sigmoidal enzymes. |
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How can allosteric enzyme activity increase and decrease? |
Regulatory enzymes are equipped with multiple regulatory sites that interact with heterotropic modulators to inhibit or activate behavior.
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What is a covalent modification? |
Results in a conformational change of an enzyme and modulated activity; most, if not all, covalent modifications are reversible due to sets of enzymes that attach and remove the modification.
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Which is the most common? |
The most common type of covalent modification is the phosphorylation of an enzyme that is catalyzed by kinases. |
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Does phosphorlylation inhibit or activate enzymes? |
Dependent upon the enzyme. |
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Besides covalent and allosteric regulation, what other ways can an enzyme be regulated? |
Feedback inhibition and feedforward activation |
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What is the energy charge equation? |
[ATP] + 1/2[ADP] ___________________ [ATP] + [ADP] + [AMP] |
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What is feedback inhibition? |
Regulatory mechanism employed within the cell whereby the product of the pathway acts as a negative modulator of key enzymes at the beginning of the pathway.
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What is feedforward activation? |
Regulatory mechanism employed within the cell whereby metabolites produced early in a pathway act as positive modulators of key enzymes at the end of the pathway or another metabolic pathway.
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What should be happening to catabolic/anabolic paths as energy charge increases/decreases? |
As energy charge increases anabolic paths are employed to resupply ADP and AMP. As energy charge decreases catabolic paths are employed to resupply ATP. |
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What is energy charge a measure of? |
Measure from 0-1 of the cellular energy status in which the ratio of adenylate molecules with phosphodiester bonds to the total adenylate pool is calculated. AMP(0), ADP(1), and ATP(2).
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How might the cell accomplish this increase/decrease in flux in response to energy change? |
Allosteric regulation of key enzymes that catalyze irreversible steps in both anabolic and catabolic paths. Using ATP, ADP, and AMP as allosteric effectors. ATP inhibits catabolic path involved enzymes. ADP and AMP inhibit anabolic involved enzymes.
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How do PFK-1/FBPase-1 illustrate the principles of metabolic control specifically in regards to energy change? |
PFK-1 catalyzes the “committed step” of glycolysis. This enzyme is allosteric and has a more effective R form and less effective T form. ATP stabilizes the T form having a inhibitory effect. AMP and ADP have opposite effects and act to activate PFK-1. FBPase-1 catalyzes the committed step of gluconeogenesis and is inhibited by AMP.
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How does PFK-1 illustrate the principles of metabolic control? |
Citrate intermediate from TCA cycle stabilizes the T form having an inhibitory effect. High citrate levels are a result of lipid biogenesis. By halting this step of glycolysis, glucose can be used in the pentose phosphate path which produces NADPH. This is a necessary reducing agent for lipid biogenesis. PFK-1 can therefore also regulate lipid biogenesis. |
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What is insulin/glucagon a sign of? |
Glucagon is a sign of low blood sugar while insulin is a sign of high blood sugar. |
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How do these hormones affect the PFK-1/FBPase-1 bypass reaction? |
Glucagon signaling sets of a signaling cascade that results in the phosphorylation of a bifunctional enzyme PFK-2/FBPase-2. This enzyme has two active sites, when glucagon binds it leads to a conformation change which leads to activation of FBPase-2 and the breakdown of F26BP. In this way the cell removes an allosteric inhibitor of FBPase-1 and allosteric activator of PFK-1 and thus gluconeogenesis flux will increase while glycolytic flux decreases. |
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What is the overall results in terms of glycolysis flux and and gluconeogenesis flux in the liver in response to these hormones? |
There will be a flux in gluconeogenesis in the liver when there is glucagon present and a flux in glycolysis when insulin is present. |
