Question

At low substrate concentration, the initial velocity of reaction is described as \_\_\_\_\_\_\_\_\_\_. However, as substrate concentration increases, the reaction saturates and reaches a \_\_\_\_\_\_\_\_\_\_.

• A. Hyperbola and Plateau
• B. Plateau and Hyperbola
• C. Straight line and Hyperbola
• D. Straight line and straight line

Hint:

Remember the two extremes of Michaelis-Menten kinetics:

\textbf{Low [S]:} First-order kinetics (rate depends on [S]). Graph is a line.
\textbf{High [S]:} Zero-order kinetics (rate is independent of [S]). Graph is a plateau at V\(_{max}\).
\textbf{Overall Shape:} A hyperbola that connects these two extremes. \end{itemize}

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This question describes the key features of a Michaelis-Menten plot, which graphs the initial reaction velocity (V\(_0\)) against the substrate concentration ([S]) for an enzyme-catalyzed reaction.

Step 2: Detailed Explanation:
The Michaelis-Menten equation is \( V_0 = \frac{V_{max}[S]}{K_m + [S]} \).
- At low substrate concentration ([S] \(\ll\) K\(_m\)), the reaction is approximately first-order with respect to [S], and the initial part of the graph is nearly a straight line.
- As substrate concentration increases, the rate of increase in velocity slows down because the enzyme's active sites are becoming occupied. The overall shape of this curve, showing the relationship between V\(_0\) and [S], is a rectangular hyperbola.
- At high substrate concentration ([S] \(\gg\) K\(_m\)), the enzyme's active sites are completely saturated with the substrate. The reaction rate becomes independent of [S] and approaches its maximum velocity (V\(_{max}\)). On the graph, this saturation is represented by the curve leveling off, forming a plateau.

Step 3: Final Answer:
The question asks to describe the overall shape of the velocity curve and the state it reaches at saturation. The curve is a hyperbola, and it reaches a plateau. Therefore, option (A) is the best description. (Note: While the very initial part of the curve is a straight line, the entire curve is described as a hyperbola).