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BC 351 Exam 4 Study GuideLecture 121. What is homeostasis? What is the steady state? What is metabolic flux? How do these relate to one another? How do they relate to the control aspects of pathways? What enzymes will be regulated? How can this lead to regulation of an entire pathway? Homeostasis is a cellular process in which a steady state is maintained, allowing the celling to respond to external stimuli. The steady state is one of non-equilibrium in which cellular components (i.e. metabolites, etc.) remain at more or less constant concentrations. Metabolic flux is the rate at which metabolites enter and pass through a pathway. These three things relate to each other in that the cell maintains homeostasis and the steady state so that it can adjust metabolic flux and metabolic pathways as necessary in response to stimuli. The enzymes that are regulated are theones that catalyze irreversible reactions, which in turn controls the reversible ones that follow them.2. What is an allosteric enzyme? How do these enzymes kinetics compare to the kinetics of the enzymescovered in lecture 7? What is the K0.5? How can their activity decrease and increase? An allosteric enzyme is one that undergoes a conformational change, resulting in an increase or decrease in activity. These enzymes exhibit a sigmoidal kinetics curve, rather than a parabolic one, which is an indicator of cooperative binding behavior and therefore means they can be regulated. The curve can be changed by adjusting K0.5 or vmax. K0.5 is a measure of the specificity of the enzyme for its substrate; in other words, it’s the Km value for allosteric enzymes; more specifically, it indicates the [S] required to reach ½ vmax. The activity of allosteric enzymes can be either negativelyor positively modulated, resulting in either decreases or increases, respectively. Negative modulators decrease either the vmax for the reaction, by adjusting kcat, or the specificity of the enzyme for its substrate, by adjusting K0.5. Positive modulators will do the opposite.3. What is a covalent modification? Which is the most common? Does it activate or inhibit enzymes? Besides covalent and allosteric regulation by what other means can enzymes be regulated? A covalent modification is the covalent binding of some additional group to an enzyme to affect its activity. The most common form of this is phosphorylation, or the addition of a phosphate group, which is carried out by kinases within the cell. It can either activate or inhibit enzymes, though it usually inhibits them. One example, however, of activation due to covalent modification is the expression or muting of genes in DNA expression. Other means by which enzymes can be regulated include protein turnover (the degradation of existing enzyme or the production of more); protein sequestration (the removal/gathering of an enzyme in a compartment other than where it usually operates, thus separating it from its substrate); and regulatory protein binding (the attachment of some kind of modulator to either increase or decrease activity). 4. What is the energy charge? What is it a measure of? What should be happening to metabolic flux of catabolic/anabolic pathways as energy charge increases/decreases? How might the cell accomplish this increase/decrease in flux in response to energy charge? In other words what is the molecular process in which metabolic output can be integrated based upon energy charge? Energy charge is a measure of the energy status, or ratio of ATP to ADP and AMP, within the cell. As energy charge increases, catabolic processes should decrease and anabolic pathways should increase; vice versa, as energy charge decreases, catabolic processes should be up-regulated while anabolic pathways should decrease in activity. The cell can achieve these changes because adenylyl compounds (ATP, ADP, AMP, etc.) are key modulators for most allosteric pathways, which meansthat their respective concentrations can tell pathways which way to go in response to changing conditions of the cell, which is permitted by the maintenance of the steady state. In other words, themolecular process by which this occurs is allosteric regulation.5. How do PFK-1 and FBPase-1 illustrate the principles of metabolic control specifically in regards to energy charge? High concentrations of ADP and AMP tell the cell to increase the activity of PFK-1, a catabolic enzyme, while AMP indicates that there should be a decrease in FBPase-1 activity. On the other hand, high levels of ATP will tell the cell to decrease PFK-1.6. What is glucagon/insulin a sign of? How do these hormones affect the PFK-1/FBPase-1 bypass reaction? What is the overall result, in terms of glycolysis flux and GNG flux in the liver cell in response to these hormones? Glucagon is released by the pancreas in response to low blood glucose to tell the liver to release glucose, while insulin is secreted in response to high blood glucose to tell the liver to absorb it. The secretion of glucagon tells the liver cell, via binding to the membrane protein (NOT transporter) called a glucagon receptor to induce a conformational change, to release glucose. The glucagon receptor gives adenylate cyclase the “green light” to convert ATP to cAMP, which then activates the pathway in which protein kinase A (PKA) uses a phosphate group from ATP to phosphorylate the bi-functional enzyme PFK-2-FBPase-2 (two domains, NOT subunits – they have the same primary structure), which then activates the FBPase-2 domain. The active FBPase-2 then breaks F26BP down in F6P to remove the activator of glycolysis/the inhibitor of GNG, thus increasing GNG flux and decreasing glycolytic flux. With insulin signaling, the opposite occurs: the membrane protein insulin receptor, causing a conformational change, induces a series of complex enzyme-catalyzed reactions that activate the enzyme protein phosphatase (PP) to remove the phosphate group from PFK-2-FBPase-2, deactivating the FBPase-2 domain and activating the PFK-2 domain, resulting in the conversion of F6P to F26BP. The presence of F26BP results in activation of glycolysis and the inhibition of GNG. [Overall: insulin  inc. glycolysis, dec. GNG; glucagon  inc. GNG, dec. glycolysis]Lecture 131. What is cellular respiration? What are its 3 phases? At what metabolite do all catabolic paths feed into? Cellular respiration is the process by which cells consume O2 and produce CO2 and H2O. The three phases are: 1) the


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CSU BC 351 - Exam 4 Study Guide

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