Fill-in-the Blank Questions
Chapter 6 Basic Concepts of Enzyme Action
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used. a) apoenzymes b) hydrolyases c) active site d) transition state e) spontaneous f) induced fit g) energy h) prosthetic group i) lock and key j) substrate(s) k) oxidoreductases l) equilibria
184
____________ The site on the enzyme where the reaction occurs.185
____________ The substance that the enzyme binds and converts to product.186
Enzymes that do not have the required cofactor bound are called ____________.187
A tightly bound cofactor might be called a(n) ____________.188
Enzymes will decrease the energy of activation but do not change the ____________ of a chemical reaction.189
A reaction that is exergonic will be ____________.190
An endergonic reaction requires an input of ____________ to proceed.191
Enzymes that transfer electrons are called ___________.192
Enzymes that cleave molecules by addition of water are called ____________.193
Which model is more appropriate to explain an enzyme binding to its substrate?Fill-in-the-Blank Questions
194
Enzymes accelerate the rate of a chemical reaction by the free energy of activation of the reaction.195
The difference between the standard-state free energy, ΔGº, and the biochemical standard-state free energy is that ΔGº refers to the standard free-energy change at .196
An enzyme that loosely binds substrate will have a level of specificity.197
Organic cofactors are referred to as .198
A reaction can occur spontaneously only if ΔG is .199
When ΔG for a system is zero, the system is at .201
The total change of free energy in a reaction depends on and .202
The difference in values for G and Go′ is in the .203
Competitive inhibitors that mimic the substrate while in the transition state are called inhibitors.Multiple-Choice Questions
204
What is the common strategy by which catalysis occurs? A) increasing the probability of product formationB) shifting the reaction equilibrium C) stabilization the transition state D) All of the above.
E) None of the above.
205
An enzyme will specifically bind its substrate because of____________ A) a tight lock and key binding mechanism.B) a high number of hydrophobic amino acids in the center of the protein. C) a large number of weak interactions at the active site.
D) additional nonprotein cofactors. E) None of the above.
206
Examples of cofactors include: A) Zn+2, Mg+2, and Ni+2.B) biotin and thiamine pyrophosphate. C) pyridoxal phosphate and coenzyme A. D) B and C.
E) All of the above.
207
A cofactor is best defined as ______________. A) another proteinB) a covalently bound inorganic molecule
C) a small molecule that holds the substrate in the active site
D) a molecule responsible for most of the catalytic activity of the enzyme E) None of the above.
208
Which of the following is true?A) Enzymes force reactions to proceed in only one direction. B) Enzymes alter the equilibrium of the reaction.
C) Enzymes alter the standard free energy of the reaction. D) All of the above.
E) None of the above.
209
The Gibbs free energy of activation is:A) the difference between the substrate and the transition state. B) the difference between the substrate and the product. C) the difference between the product and the transition state. D) All of the above.
E) None of the above.
210
At equilibrium, the Gibb’s free energy is ___________. A) a positive valueB) neutral
C) a negative value
D) zero
E) one
211
The rate of a reaction, or how fast a reaction will proceed, is best determined by __________.A) R
B) G‡
C) Gº′
D) H
E) None of the above.
212
The relationship between Go′ and G is best described as ______________.A) determined by the temperature B) described by changes in Keq
C) differ from standard state to physiological or actual concentrations of reactants and products D) dependent on the reaction mechanism of the reaction
E) differ only in terms of the types of reactions used for each value
213
For the two reactions a) A→B Go′ = 2 kJmol-1 and b) X→Y Go′ = –3.5 kJmol-1, which ofthe following statements is correct?
A) Reaction a is not spontaneous at cellular concentrations. B) Reaction b will react very quickly.
C) Reaction a is a more thermodynamically favorable reaction than b. D) Neither reaction is reversible.
214
A graph of product versus time (as in Fig. 6.2 in your textbook) for an enzyme is determined to be hyperbolic. Why does the amount of product level off as time increases?A) The reaction has reached equilibrium, that is, the forward and reverse reactions are occurring at a fixed rate.
B) There is a product inhibition of the enzyme. C) The reaction runs out of reaction materials. D) The enzyme has finished accelerating the reaction. E) None of the above.
215
The free energy of activation is _______________.A) the amount of chemical energy available in the transition state B) the difference in free energy between the substrate and product C) the free energy gained by adding a catalyst
D) the difference in free energy between the transition state and the substrate E) All of the above.
216
The molecular structure that is short-lived and neither substrate nor product is known as_______.A) substrate analog B) transition state
C) free energy stabilization state D) catalysis state
E) equilibrium intermediate
217
Riboflavin is a water-soluble organic substance that is not synthesized by humans.Metabolically, it is chemically converted into a substance called flavin adenine dinucleotide, which is required by succinate dehydrogenase. Which of the following statements is most correct?
A) Riboflavin is a coenzyme.
B) Flavin adenine dinucleotide is a vitamin. C) Succiniate dehydrogenase is a coenzyme. D) Flavin adenine dinucleotide is a coenzyme.
218
The active site of an enzyme_____________. A) is a series of amino acids that bind the enzymeB) is a linear sequence of amino acids that react with each other C) binds covalently to the substrate
D) allows water to enter into the solvate the substrate E) None of the above.
219
The conversion of glucose-6-phosphate to fructose-6-phosphate is catalyzed by an isomerase enzyme. Glucose-6-phosphate was mixed with the enzyme under standard conditions and the reaction was allowed to come to equilibrium. If the Keq′ is 0.50 and the equilibrium [glucose-6-phosphate] is 1.43 M, what is the equilibrium [fructose-6-phosphate]?
A) 1.00 M
B) 1.33 M
C) 0.667 M D) 0.250 M E) 0.150 M
220
The conversion of glucose-6-phosphate to fructose-6-phosphate is catalyzed by an isomerase enzyme. Glucose-6-phosphate was mixed with the enzyme under standard conditions and the reaction was allowed to come to equilibrium. If the Keq′ is 0.50, what is the G°′ in kJ/mol?A) +0.99 B) +1.71
C) 0, as defined by equilibrium conditions D) –0.99
E) –2.27
221
The conversion of glucose-6-phosphate to fructose-6-phosphate is catalyzed by an isomerase enzyme. Under cellular conditions (37oC), the glucose-6-phosphate is 6.6 μM and the fructose-6-phosphate is 1.3 μM. If the Keq′ is 0.50, what is the ΔG in kJ/mol? (Hint: Use the G°′ from
the previous question.) A) +4.19
B) –1.81 C) –4.03 D) –2.50 E) –1.75
222
That many transition-state analogs bind more tightly than the native substrate reinforces the concept that:A) transition-state analogs are planar structures.
B) transition-state analogs are highly charged at physiological pH. C) binding to the transition state is through a lock-and-key-mechanism. D) transition-state analogs are hydrophobic.
E) binding to the transition state is through an induced-fit mechanism.