Home / AP Biology 3.2 Environmental Impacts on Enzyme Function- Exam Style questions – FRQs

AP Biology 3.2 Environmental Impacts on Enzyme Function- Exam Style questions - FRQs- New Syllabus

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Question

Figure \(1\) shows the reactions of the metabolic pathway used to synthesize amino acid \(B\) from amino acid \(A\) in cells.

Figure \(1\). Synthesis of amino acid \(B\) from amino acid \(A\)
(A) Describe a characteristic of an enzyme’s active site that allows it to catalyze a specific chemical reaction.
(B) Based on Figure \(1\), explain how the binding of amino acid \(A\) to enzyme \(1\) is regulated by amino acid \(B\).
(C) Using the information in Figure \(1\), identify the product of the reaction catalyzed by enzyme \(2\): intermediate \(X\), intermediate \(Y\), or amino acid \(B\).
(D) Based on Figure \(1\), explain how a change in pH could affect enzyme \(3\) in such a way that amino acid \(B\) cannot be produced.

Most-appropriate topic codes (AP Biology \(2025\)):

• Topic \(3.1\) — Enzymes: Shape and charge of the active site determine substrate binding and catalytic specificity — part (A)
• Topic \(3.3\) — Cellular Energy: Metabolic pathways proceed in sequential steps, where the product of one reaction becomes the reactant for the next — parts (B), (C)
• Topic \(3.2\) — Environmental Impacts on Enzyme Function: Changes in pH can alter enzyme structure, active-site shape, and substrate binding — part (D)
• Science Practice \(2\) — Visual Representations: Interpreting a pathway diagram to explain regulation and identify products — parts (B), (C), (D)
▶️ Answer/Explanation

(A)
The active site is able to bind to a specific substrate or amino acid.
The shape and charge of the active site of an enzyme are compatible with a specific substrate or amino acid.
The active site positions the substrate or amino acid in a way that makes the reaction more likely.
The active site can induce fit and stress bonds so that a reaction is more likely to occur.
Summary: an enzyme works on a specific substrate because its active site has the correct shape and chemical properties.

(B)
Amino acid \(B\) inhibits the binding of amino acid \(A\) to enzyme \(1\).
Amino acid \(B\) binds to an allosteric site of enzyme \(1\) and prevents amino acid \(A\) from binding to enzyme \(1\).
The binding of amino acid \(B\) causes the enzyme to change shape and prevents amino acid \(A\) from binding to enzyme \(1\).
Summary: this is feedback inhibition, in which the final product shuts down an earlier step in the pathway.

(C)
The product of the reaction catalyzed by enzyme \(2\) is intermediate \(Y\).
Because enzyme \(2\) acts after intermediate \(X\) is formed and before enzyme \(3\) acts, the next product in the pathway is intermediate \(Y\).

(D)
A change in pH could change the structure, active site, or overall shape of enzyme \(3\) so that intermediate \(Y\) or the substrate cannot bind.
A change in pH could denature enzyme \(3\) so that intermediate \(Y\) or the substrate cannot bind.
As a result, enzyme \(3\) would no longer catalyze the final step, so amino acid \(B\) would not be produced.
Summary: pH affects enzyme structure, and if the enzyme loses the right shape, the pathway stops.

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