Bio102 Problems
Enzymes and Cellular Energy
1. Spontaneous chemical reactions
A. have a negative G value.
B. create additional energy.
C. never require a catalyst.
D. are usually endergonic.
E. happen quickly in a test tube.
2. Which one of the following statements in NOT an accurate description of a catalyst?
A. Catalysts increase the rate of a chemical reaction.
B. Catalysts are considered to be one of the reactants of the chemical reaction.
C. Catalysts do not shift the equilibrium of a chemical reaction.
D. Catalysts decrease the amount of activation energy needed for a chemical reaction to occur.
E. Catalysts may be proteins.
3. The equilibrium constant for a chemical reaction is determined by
A. the initial substrate concentration.
B. the G for the reaction.
C. the activation energy for the reaction.
D. the enzyme concentration.
E. the amount of heat available.
4. Endergonic reactions
A. are commonly regulated by feedback inhibition.
B. never happen in a cell.
C. can be catalyzed by an enzyme.
D. are generally spontaneous.
E. always happen at a slow rate.
5. The presence of a catalyst changes which one of the following characteristics of a chemical reaction?
A. G
B. Substrate Energy
C. Product Energy
D. Activation Energy
E. Equilibrium
6. Addition of an enzyme can change which characteristic of a chemical reaction?
A. Change in free energy
B. Equilibrium constant
C. Activation energy
D. Michaelis constant
E. Substrate energy
7. In the lab, we looked at the reaction of pyrocatechol  quinone, catalyzed by the enzyme tyrosinase.
We were able to easily follow the progress of this reaction because the quinone was brown.
7A. Is the pyrocatechol  quinone spontaneous or nonspontaneous? Or can we tell? Please explain
your answer.
7B. When we were getting ready for lab this week, we found the bottle of pyrocatechol that we used in
this class last fall (6 months ago). Even though there was no enzyme in the bottle, the solution had
turned brown. Please briefly explain why the solution turned brown.
8. The reaction 2 NH3  N2 + 3 H2 is endergonic. On the graph below, draw the energy diagram for this
reaction. Show what corresponds to the G value on the diagram.
Is this reaction chemically spontaneous or
nonspontaneous? How do you know?
This reaction can be catalyzed by the
addition of iron. Does adding the catalyst
change this energy diagram? If so, draw a
dashed line and explain how you knew
where to draw it. If not, explain why not.
Free
Energy
Instead of adding iron, this reaction can be
speeded up by adding heat. Does adding
heat change this energy diagram? If so,
draw a dotted line and explain how you
knew where to draw it. If not, explain why
not.
Progress of the Reaction
9. All catalysts
A. are enzymes.
B. increase the rate of the reaction.
C. increase the Keq of the reaction.
D. decrease the Keq of the reaction.
E. briefly violate the First Law of Thermodynamics.
10A. Triglycerides are synthesized when fatty acids are added to what three-carbon molecule?
3 Fatty Acids + _________________
Triglyceride + H2O
10B. The G for this reaction is -5 kcal/mole and the activation energy (EA) is 2 kcal/mole. Circle each
term below that correctly describes this reaction.
Condensation
Endergonic
Isogonic
Exergonic
Nonspontaneous
Hydrolysis
Spontaneous
10C. Draw the energy diagram for this reaction in the
chart on the left. Be sure to label your axes.
10D. Now, suppose we add the enzyme Acyltransferase
which catalyzes this reaction. Use a dashed line to show
how the enzyme changes the energy diagram. Also record
the new G and EA (with units!).
G
= ______________
EA = ______________
10E. When this reaction reaches equilibrium without the enzyme, which statement is true? Circle one.
No fatty acids
are present
Few fatty acids
are present
Equal amounts of
fatty acids and
triglycerides are
present
Few triglycerides
are present
No
triglycerides
are present
Can’t tell for
certain
10F. When this reaction reaches equilibrium with the enzyme, which statement is true? Circle one.
No fatty acids
are present
Few fatty acids
are present
Equal amounts of
fatty acids and
triglycerides are
present
Few triglycerides
are present
No
triglycerides
are present
Can’t tell for
certain
10G. The enzyme Acyltransferase would be expected to be in which organelle?
____________________________
10H. The Keq value for this reaction is…
Greater
than one
Equal
to one
Less
than one
Can’t tell
11. Sucrase catalyzes the breakdown of sucrose into glucose and fructose effeciently at a neutral pH.
Substantially raising the pH of the reaction changes some of the aspects of that reaction and leaves
others unchanged.
Will raising the pH affect the G of the reaction? Please explain.
Will raising the pH affect the primary structure of the enzyme? Please explain.
Will raising the pH affect the tertiary structure of the enzyme? Please explain.