GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Enzyme Kinetics
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #1 : Help With Enzyme Kinetics
A researcher is studying the rate of an enzyme-catalyzed reaction by placing increasing amounts of substrate into a solution containing the enzyme. After a certain concentration, the rate of the reaction plateaus and does not go any higher. What has happened?
The enzyme has become denatured
The reaction rate has only momentarily plateaued; given enough time it will increase
The enzyme has become saturated
The concentration of enzyme is so small that the reaction has stopped occurring completely
The enzyme has become saturated
If the reaction rate has plateaued, this indicates that the enzyme has reached saturation. At this point, every active site on every molecule of enzyme is actively catalyzing the reaction as quickly as it can. The only way to change the reaction rate, at this point, would be to increase the concentration of the enzyme in the solution. Further increasing substrate concentration will have no effect.
We know that the enzyme has not become denatured because the reaction is still occurring. The rate of the reaction is constant during the plateau, and does not drop to zero.
Example Question #2 : Enzymes
In a Lineweaver-Burk plot, what quantity determines the y-intercept?
A Lineweaver-Burk plot is a way to graphically represent enzyme kinetics. It is convenient because several portions of the graph readily display important information, such as rate constants. The y-intercept in particular is useful because it represents the reciprocal of the maximum velocity. The x-intercept describes the negative reciprocal of the Michaelis constant. The slope is the quotient of the Michaelis constant over the maximum velocity.
Example Question #3 : Enzymes
What information is contained in a Lineweaver-Burk plot that is not present in a standard Michaelis-Menten plot?
None of these answers
None of these answers
The two plots contain the same information. A Michaelis-Menten plot shows the relationship between initial reaction rate concentration of substrate (
Example Question #2 : Enzymes
Which of the following changes will alter 
Addition of a competitive inhibitor
Addition of a non-competitive inhibitor
None of these options; 
Increasing substrate to supraphysiological concentrations
Addition of a non-competitive inhibitor
The only option that will alter the 
Addition of a competitive inhibitor will alter the 
Example Question #1 : Help With Enzyme Kinetics
A catalyst is an enzyme that promotes a reaction. In terms of free energy, what does a catalyst change about the reaction to promote the reaction proceeding?
Catalysts induce a global increase of entropy to the product state of the reaction, making it more favorable and thus occurring at a faster rate.
Catalysts increase the rate of the reaction by reducing the free energy of the transition state, which lowers the activation energy.
Catalysts increase the rate of the reaction by increasing the free energy of the transition state, which increases the activation energy.
Catalysts increase the amount of energy contributed to the reaction through heat from the reaction environment, thus increasing the rate of the reaction.
Catalysts increase the rate of reaction by decreasing the free energy of the transition state, which increases the activation energy.
Catalysts increase the rate of the reaction by reducing the free energy of the transition state, which lowers the activation energy.
During a reaction, the reactants must pass through high-energy transition states before they evolve into the products. The catalyst reduces the free energy of this transition state, thus making it 'easier' for the reactant to undergo the chemical reaction since the activation energy has been lowered.
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