Part A Given what you know about the function of the glyoxylate cycle and the regulation of the citric acid cycle, choose control mechanisms that might regulate the glyoxylate cycle. Check all that apply. increasing the availability of glucose as the carbon source activation of isocitrate lyase by acetyl-CoA or fatty acids inhibition of isocitrate lyase by succinate substrate-level control of citrate synthase substrate-level control of succinyl-CoA synthetase activation of succinic dehydrogenase
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How is flux activity through the citric acid cycle controlled? control of isocitrate dehydrogenase control of α-ketoglutarate dehydrogenase control of citrate synthase At many points, including all of the above.
Rabeya Z.
Activation of pyruvate carboxylase by acetyl-CoA This is a signal that part of the available pyruvate can be metabolized into oxaloacetate when the energy charge is low and production of additional ATP through the citric acid cycle is required. This is a signal that pyruvate can be oxidized in the citric acid cycle instead of being shunted into gluconeogenesis. In addition, it is a signal of activated carbohydrate metabolism. This is a signal that pyruvate can be oxidized in the citric acid cycle as well as being shunted into gluconeogenesis. In addition, it is a signal of activated fat metabolism. This is a signal that pyruvate can be shunted into gluconeogenesis instead of being oxidized in the citric acid cycle. In addition, it is a signal of unbalanced fat and carbohydrate metabolism. Activation of pyruvate dehydrogenase kinase by NADH Inhibition of isocitrate dehydrogenase by NADH This tends to activate pyruvate dehydrogenase when the level of NADH is sufficient for ATP production via the respiratory chain and, hence, to make pyruvate unavailable for other purposes. This tends to activate pyruvate dehydrogenase when the level of NADH is sufficient for ATP production via the citric acid cycle and, hence, to increase the oxidation of lipids and carbohydrates. This tends to inactivate pyruvate dehydrogenase and activate pyruvate carboxylase, increasing oxaloacetate production and, hence, activating gluconeogenesis. This tends to inactivate pyruvate dehydrogenase when the level of NADH is sufficient for ATP production via the respiratory chain and, hence, to make pyruvate available for other purposes. Activation of isocitrate dehydrogenase by ADP This is a signal to reduce flux through the citric acid cycle when the metabolism of acetyl-CoA through the glyoxylate pathway is more preferred. This is a signal to reduce flux through the citric acid cycle when an additional amount of acetyl-CoA is needed for lipid biosynthesis. This is a signal to increase flux through the citric acid cycle when the metabolism of acetyl-CoA through the glyoxylate pathway is less preferred. This is a signal to reduce flux through the citric acid cycle when levels of reduced electron carriers are adequate for energy generation. Inhibition of alpha-ketoglutarate dehydrogenase by succinyl-CoA The accumulation of ADP provides a signal to activate isocitrate dehydrogenase and thereby increase alpha-ketoglutarate levels in the organism, preventing ATP consumption in the process of glutamine desamination. When the energy charge is high, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase succinate production for the electron transport chain. When the energy charge is low, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase the oxidation of nutrients for ATP production. When the energy charge is high, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase the oxidation of nutrients for protein production. Activation of pyruvate dehydrogenase phosphatase by Ca2+ This serves as a general indicator that when an energy-rich substrate (succinyl-CoA) is abundant, flux through the citric acid cycle can be reduced. This serves as a signal that there is an insufficient amount of NAD+, FAD, and flux through the electron transport should be increased. This allows for an increase in alpha-ketoglutarate accumulation and thereby increases the rate of amino acid transamination. This allows for the reversal of reversible stages of the citric acid cycle to produce additional pyruvate, which can be used in gluconeogenesis at high glucose levels in the blood. Ca2+ interacts with active sites of four proteins that participate in the contraction of vertebrate muscle, which places a huge demand on ATP production. Ca2+ is a critical signaling molecule for contraction in vertebrate muscle, which places a huge demand on ATP production. Ca2+ activates PDH through interaction with an active site of the enzyme when a huge amount of ATP molecules is needed for protein synthesis activation. Ca2+ mediates the stimulation of PDH activity during muscle contraction, which can produce a huge amount of ATP molecules.
Shaiju T.
3a. Carbon flux through the glyoxylate shunt or the TCA cycle is controlled by altering the activity of the enzyme isocitrate dehydrogenase (Icd). Please explain how this control occurs. 3b. Scientists have stated that this type of control carbon flux ultimately saves the cell energy because carbon flux control occurs at the level of the enzyme and not at the level of transcription/translation. Why do you think that this statement is true? 3c. A number of molecules ultimately effect the activity of Icd. Please list these molecules and explain hypothesize why evolution chose these molecule to effect isd activity to control flux through the TCA cycle and glyoxylate shunt.
Sri K.
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