Just as every enzyme has an optimal temperature it also has an optimal pH at which it's most active. The activity decreases when the pH tends to get lower or higher than the optimum. This is mainly because the amino acid side chains act as weak acids and bases performing critical functions in the enzyme active site. Enzymes like pepsin have a ...
The expert explains how the rate of many enzyme catalyzed reactions varies with pH. The types of amino acids must be at the active site of an enzyme if its rate decreases at high pH is given.
Multiple Choice Quiz in Biology
Biology Quiz: Energy, Enzymes, and Catalysis
1. Which statement about enzyme catalyzed reactions is NOT true?
A. Enzymes form complexes with their substrates.
B. Enzymes lower the activation energy for chemical reactions.
C. Enzymes change the K eq for chemical reactions.
D. Many enzymes change shapes slightly when substrate binds.
E. Reactions occur at the "active site" of enzymes, where a precise 3D orientation of amino acids is an important feature of catalysis.
2. The equilibrium constant for the conversion of the disaccharide sucrose to the simple sugars glucose and fructose is 140,000. What can you conclude about the reaction: sucrose + H2O glucose + fructose?
A. It is a closed system.
B. It never reaches equilibrium.
C. It is spontaneous, starting with sucrose.
D. The equilibrium constant increases when the starting concentration of sucrose is increased.
E. At equilibrium, the concentration of sucrose is much higher than the concentrations of glucose and fructose.
3. In regards to the kinetics of an allosteric enzyme, which of the following graphs shows the results of reaction rate vs substrate concentration for an allosteric enzyme in the absence and presence of an allosteric inhibitor?
E. none of the graphs
4. To overcome an energy barrier between reactants and products in a chemical reaction, energy must be provided to get the reaction started. This energy, which is recovered as the reaction proceeds, is called:
A. activation energy
B. initiation energy
C. reaction energy
D. kinetic energy
E. potential energy
5. In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as you increase the concentration of acetaldehyde. Eventually the rate of the reaction reaches a maximum, where further increases in the concentration of acetaldehyde have no effect. Why?
A. All of the alcohol dehydrogenase molecules are bound to acetaldehyde molecules
B. At high concentrations of acetaldehyde, the activation energy of the reaction decreases
C. The enzyme is no longer specific for acetaldehyde
D. At high concentrations of acetaldehyde, the change in free energy of the reaction decreases
6: Equilibrium constant for ionization of acetic acid.
The equilibrium constant for the ionization of acetic acid,
is 0.00002. What can you conclude about this reaction?
A. It is a closed system.
B. At equilibrium, the concentration of CH3COOH is much higher than the concentrations of CH3COO- + H+.
C. It never reaches equilibrium.
D. It is spontaneous, starting with CH3COOH.
E. The equilibrium constant increases when the starting concentration of CH3COOH is increased.
7. In describing the reaction rate for a chemical reaction, which of the following statements about reaction rate is NOT true?
A. Reaction rate is the speed at which the reaction proceeds toward equilibrium.
B. Reaction rate is governed by the energy barrier between reactions and products
C. Enzymes can accelerate the rate of a reaction.
D. Reaction rates are not sensitive to temperature.
E. None of these.
8. When considering the features of an exergonic reaction, exergonic reactions:
A. Release energy
B. Are spontaneous reactions
C. Have an equilibrium constant greater than 1
D. Can be coupled to energonic reactions.
E. All statements are true.
9. In the Kinetics of an enzyme reaction with a non-competitive inhibitor, which of the following graphs shows the results of reaction rate vs substrate concentration for an non-allosteric enzyme in the absence and presence of a non-competitive inhibitor (non-competitive inhibitors bind to an enzyme at a site different than the active site)?
E. None of the graphs
10. In describing enzyme feature, enzymes:
A. are composed primarily of polypeptides, which are polymers of amino acids.
B. can bind prosthetic groups such as metal ions that participate in enzyme reactions
C. have defined structures.
D. bind their substrates at active sites.
E. all statements are true
11. In understanding activation energy, activation energy is
A. energy that must be added to get a reaction started, which is recovered as the reaction proceeds.
B. difference in energy between reactants and products.
C. Energy that is lost as heat.
D. Free energy
E. Equal to the entropy times the absolute temperature.
12. In thinking about energy that requires reactions in biological systems, energy-requiring reactions can occur in biological systems because enzymes allow their coupling to other reactions with:
A. an increase in entropy
B. a low activation energy
C. no inhibitors
D. products of lower free energy than the reactants
13. In reference to the equilibrium constant for hydrolysis of glucose-6-phosphate
The equilibrium constant for the reaction, glucose 6-phosphate + water glucose + phosphate, is 260. What can you conclude about this reaction:
A. It is a closed system
B. It never reached equilibrium.
C. Starting with glucose 6-phosphate, it is not spontaneous.
D. At equilibrium, the concentration of glucose is much higher than the concentrations of glucose 6-phosphate.
E. At equilibrium, the concentration of glucose is much higher than the concentrations
14. When interpreting an "S-shaped" enzyme kinetics curve
The graph shows the results of reaction rate vs substrate concentration for a(n):
A. enzyme plus a competitive inhibitor
B. enzyme plus a non-competitive inhibitor
C. allosteric enzyme C
D. enzyme plus an un-competitive inhibitor
E. two enzymes competing for the same substrate
15: Interpreting the plateau of an enzyme kinetics curve:
In the graph reaction rate vs substrate concentration, the reason that the curve reaches a plateau, and does not increase any further at high substrate concentration is that:
A. the active site is saturated with substrate
B. there is a competitive inhibitor present
C. there is a non-competitive inhibitor present
D. the allosteric enzyme is locked in an inactive conformation
E. all substrate has been converted to product
16. When speaking about energy requiring and energy yielding reactions which answer makes the following statement correct:
The result of a(n) __________ reaction is that energy is released. Energy must be added for a(n) __________ reaction to proceed.
A. enzyme catalyzed, non-spontaneous
B. exergonic, endergonic
C. endergonic, spontaneous
D. catalytic, non-catalytic
E. oxidative, hydrolysis