Multiple Choice
The image at right shows which of the following aspects of enzymatic catalysis?
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6. Enzymes and Enzyme Kinetics
Enzymes
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Which of the following is changed by the presence of an enzyme in a reaction?
A
Standard free energy change ($\Delta G$)
B
Equilibrium constant ($K_{eq}$)
C
Activation energy ($E_a$)
D
Overall enthalpy change ($\Delta H$)
Verified step by step guidance1
Understand the role of enzymes in biochemical reactions: Enzymes are biological catalysts that speed up reactions by lowering the activation energy ($E_a$), which is the energy barrier that must be overcome for the reaction to proceed.
Clarify that enzymes do not alter the thermodynamic properties of a reaction, such as the standard free energy change ($\Delta G$), equilibrium constant ($K_{eq}$), or overall enthalpy change ($\Delta H$). These properties are intrinsic to the reaction and depend on the reactants and products, not the presence of an enzyme.
Focus on the activation energy ($E_a$): Enzymes provide an alternative reaction pathway with a lower activation energy, making it easier for reactants to be converted into products. This is the key property that enzymes change in a reaction.
Explain how lowering the activation energy affects the reaction rate: By reducing $E_a$, enzymes increase the number of reactant molecules that have sufficient energy to reach the transition state, thereby accelerating the reaction without altering the equilibrium position.
Summarize the concept: The presence of an enzyme changes the activation energy ($E_a$) of a reaction, facilitating the process, but does not affect the thermodynamic properties like $\Delta G$, $K_{eq}$, or $\Delta H$.
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