1. Which of the following statements about the transition state of an enzyme-cat
ID: 144724 • Letter: 1
Question
1. Which of the following statements about the transition state of an enzyme-catalyzed reaction is false? (1pt)
A. It is a transient intermediate formed during the conversion of substrate to product.
B. It has a lower free energy than either substrate or product.
C. It is the least stable species along the enzyme reaction pathway.
D. It is stabilized upon enzyme binding to it.
E. Its rate of formation determines the velocity of the reaction.
3. Birds in the area have been dying at an unusually high rate, and it appears to be due to their ingestion of an invasive species of berries. You isolate a chemical compound from the berries that inhibits ATP synthase, the enzyme responsible for making ATP in the electron transport chain. To further characterize this new inhibitor, you collect the following data:
[inhibitor], in mM Vo, in mM/min -inhibitor Vo, in mM/min +inhibitor 0.2 5.0 2.0 0.4 7.5 3.0 0.8 10.0 4.0 1.0 10.7 4.3 2.0 12.5 5.0 4.0 13.6 5.5
Which of the following statements is correct? (3pts)
A. The KM increased in the presence of the inhibitor.
B. The Vmax increased in the presence of the inhibitor.
C. This is a noncompetitive inhibitor.
D. This inhibitor likely binds within the active site of the enzyme.
4. Enzyme X has an ionizable side chain in its active site and is therefore regulated by pH. Given the velocity versus pH diagram for Enzyme X below, which statement is correct? (2pts)
A. This enzyme works best when the side chain is positively charged.
B. This enzyme works best when the side chain is negatively charged.
C. The addition of H+ ions will activate Enzyme X.
D. The ionizable side chain appears to have a pKa of 10.
E. The ionizable side chain is likely critical for forming an ionic bond with the side chain of a glutamate or aspartate residue.
Explanation / Answer
Answer to Q1:
Transient state is an intermediate stage between the substrate and product. It has an higher free energy than either the substrate or product, thus its the most unstable species. It stabilises only after enzyme binds to it. If transient state is achieved early at lower energy, then velocity of reaction also increases.
Thus, the incorrect statement should be
B. It has a lower free energy than either substrate or product.
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