QUESTION I-2000

1. The effects of pH and temperature were studied for an enzyme-catalyzed reaction. The following results were obtained.

a) How do (1) temperature and (2) pH affect the activity of this enzyme? In your answer, include a discussion of the relationship between the structure and the function of this enzyme, as well as a discussion of how structure and function of enzymes are affected by temperature and pH.

b) Describe a controlled experiment that could have produced the data shown for either temperature or pH. Be sure to state the hypothesis that was tested here.

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AP® BIOLOGY
1999 SCORING GUIDELINES

Question I

Part a. (maximum 6 points)

Optimum temperature and pH concept [must include both temp and pH]

Enzyme/Substrate Fit concept (function dependent on conformation complernentarity between enzyme and substrate)

Tertiary (and sometimes quarternary) structure determines function

• Description of enzyme structure or function, e.g.

Structure

Function

Elegant description of primary to tertiary or primary to quarternary levels of structure

Increases rate of reaction

Protein folding/coiIing

Increases proximity of reactants

Co-enzymes/co-factors

Decreases activation energy of the catalyzed reaction

Zymogens

Decreases time to reach equilibrium

Allosteric effectors

Induced fit and/or orbital steering ("bond stress")


Denaturation concept [temp and/or pH] linked to decreased enzyme activity (e.g. "denaturation" in context or unfolding or change in 3D shape. not "enzyme breaks down")

How temperature affects conformation (increased temperature breaks specific bonds e.g. hydrogen, Van dcr Wuals, eljsrtllide bridges)

How pH affects conformation (change in H concentration causes a change in specific bond interactions, e.g. hydrogen: ionic, R-group interactions)

Kinetics (increased or decreased molecular movement ) linked to effect on enzyme activity due to increase or decrease in temperature up to the optimum.


Part b. (maximum 6 points)

Experimental design must be relevant to the data shown

What is measured (e.g. product formed or substrate used)

How is it measured (titration or spectrophotometry or color change or bubbles counted. etc.)

• The independent variable (temperature/pH) is manipulated to produce the results at least 3 data points are identified]

• The described experiment could produce these data
Experimental design included sufficient range, varied the temp/pH of the reaction mix not the enzyme, what was measured, and how it was measured)

• Held experimental factors constant (specified at least one)

• Specified a control group for comparison (no enzyme or boiled enzyme or no Substrate)

Verified results (e.g. repeated trials: results represent an average)

Hypothesis clearly related to experiment of choice, and clearly identified as a hypothesis can use the if/then... form.


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