ATP is a substrate for citrate synthase.

Question

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The statement to evaluate is: 'ATP is a substrate for citrate synthase.'
Option 1: True. This claim is not accurate because citrate synthase catalyzes the first step of the citric acid cycle by combining acetyl-CoA with oxaloacetate to form citrate. ATP is not a substrate in this reaction; the substrates are acetyl-CoA and oxaloacetate, and the reaction does not consume ATP in its canonical catalytic step. Misconceptions might arise if a student confuses energy carriers with substrates, but in biochemistry, ATP is typically involved later in regulation or in reactions where phosphorylation is involved, not as a direct substrate for citrate synthase.
Option 2: False. This statement correctly reflects the role of citrate synthase. In the catalytic cycle, citrate synthase uses acetyl-CoA and oxaloacetate to form citrate, with water facilitating the hydrolysis step that helps drive the reaction forward. There is no substrate role for ATP in this particular enzymatic step, and ATP is not consumed or required as a reactant here. The enzyme’s mechanism relies on the formation of a carbon–carbon bond between acetyl group and oxaloacetate, not on ATP hydrolysis or allosteric activation by ATP binding at the catalytic site.
Additional context: In metabolic pathways, ATP can influence reaction flux through energy charge or allosteric regulation, but the core substrate requirement for citrate synthase is acetyl-CoA and oxaloacetate. Recognizing the specific substrates for each enzyme prevents the common mix-up between energy carriers and actual reactants in a given enzymatic step.
In summary, the option claiming ATP is a substrate is incorrect because enzymatic catalysis by citrate synthase uses acetyl-CoA and oxaloacetate, not ATP, as substrates, making the True option an invalid characterization of the enzyme’s substrates.

ATP is a substrate for citrate synthase.

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