UBCH 250 Chapter 8

Match the each term with its definition. 1) reaction coordinate 2) ΔG° 3) ΔG‡ A) the higher point on the energy curve B) the plot of the reaction progress as a function of time C) the free energy of the reaction A) 1:B; 2:C; 3:A B) 1:A; 2:C; 3:B C) 1:C; 2:A; 3:B D) 1:B; 2:A; 3:C

A) 1:B; 2:C; 3:A

Match each of the following terms from the Michaelis-Menten equation to its correct definition. 1) V max 2) k cat 3) k cat/K M 4) K M A) substrate concentration at 0.5 V max B) rate of a reaction when enzyme is saturated with substrate C) enzyme efficiency D) number of substrate molecules turned over by enzyme A) 1:B; 2:D; 3:C; 4:A B) 1:C; 2:D; 3:A; 4:B C) 1:B; 2:C; 3:D; 4:A D) 1:D; 2:B; 3:A; 4:C

A) 1:B; 2:D; 3:C; 4:A

Please match each cofactor with its function. 1) thiamine pyrophosphate 2) coenzyme A 3) biotin 4) NAD+ A) CO2 activation/transfer B) oxidation/reduction C) activation of aldehydes D) acyl group transfer A) 1:C; 2:D; 3:A; 4:B B) 1:A; 2:D; 3:C; 4:B C) 1:C; 2:B; 3:A; 4:D D) 1:B; 2:C; 3:D; 4:A

A) 1:C; 2:D; 3:A; 4:B

Which of the following statements about the various methods of enzyme inhibition is NOT true? A) Competitive inhibitors bind at a different site than substrate, altering the ability of the enzyme to bind its native target. B) Noncompetitive inhibitors bind at a different site than substrate, altering the ability of the enzyme to bind its native target. C) Uncompetitive inhibitors bind at a different site than substrate but only after enzyme has bound its native target. D) Irreversible inhibitors, primarily because they covalently modify an enzyme, are often toxic.

A) Competitive inhibitors bind at a different site than substrate, altering the ability of the enzyme to bind its native target.

Covalent modification can either activate or inhibit enzymes. A) True B) False

A) True

Feedback regulation of a metabolic pathway can either be activation or inhibition. A) True B) False

A) True

In an enzyme-catalyzed reaction, the lifetime of the transition state is similar to the vibrational frequencies of covalent bonds. A) True B) False

A) True

Enzymes work by _____. A) reducing EA B) increasing the potential energy difference between reactant and product C) adding a phosphate group to a reactant D) decreasing the potential energy difference between reactant and product E) adding energy to a reaction

A) reducing EA

What name is given to the reactants in an enzymatically catalyzed reaction? A) substrate B) EA C) products D) active sites E) reactors

A) substrate

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again? A) Add more inhibitor to speed up the reaction. B) Add more substrate; it will outcompete the inhibitor and increase the reaction rate. C) Increase the temperature. D) Increase the pH.

B) Add more substrate; it will outcompete the inhibitor and increase the reaction rate.

A stopped-flow apparatus is used to measure rates of pre-steady state slow enzymatic reactions. A) True B) False

B) False

Coenzymes or cofactors are irreversibly changed during catalysis. A) True B) False

B) False

Electrostatic catalysis proceeds via covalent bonding interactions. A) True B) False

B) False

Non-catalyzed biochemical reactions always occur at physiological useful timescales. A) True B) False

B) False

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme? A) Removing the irreversible inhibitor should get the reaction working again. B) The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. C) Adding more substrate will increase the rate of reaction. D) Adding more inhibitor should get the reaction up to speed again.

B) The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

An enzyme _____. A) increases the EA of a reaction B) is an organic catalyst C) can bind to nearly any molecule D) is a source of energy for endergonic reactions E) is an inorganic catalyst

B) is an organic catalyst

A second-order reaction: A) has a rate constant with units of (time)-1. B) is characterized by two molecules coming together to form a product. C) occurs when one substrate is converted into one product. D) only occurs in multistep processes. E) is the rate-limiting step of a reaction.

B) is characterized by two molecules coming together to form a product.

Which of the following statements BEST describes the Michaelis-Menton constant KM? A) It is numerically equal to the affinity between the enzyme and its substrate. B) It has units of concentration. C) It is numerically equal to the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction. D) It is a measure of the rate of a catalytic process. E) It is a measure of enzyme efficiency.

C) It is numerically equal to the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction.

The lock and key model of substrate binding and enzymatic catalysis explains: A) the catalytic mechanism. B) structural changes that occur on substrate binding. C) substrate specificity. D) formation of a transition state. E) the release of product.

C) substrate specificity.

Match each function with the name of a major enzyme class. 1) transfer functional groups between molecules 2) catalyze intramolecular rearrangements 3) catalyze redox chemistry 4) catalyze the joining of two molecules together A) oxidoreductases B) transferases C) hydrolases D) lyases E) isomerases F) ligases A) 1:B; 2:C; 3:D; 4:F B) 1:B; 2:F; 3:C; 4:D C) 1:C; 2:E; 3:D; 4:F D) 1:B; 2:E; 3:A; 4:F

D) 1:B; 2:E; 3:A; 4:F

Which of the following describes a mechanism that enzymes use to achieve their rate enhancement of reactions? A) altering the reaction pathway to include intermediate states B) distortion of the substrate or active site, which, in effect, lowers the energy of activation C) preferential binding to the transition state through complementary non-covalent interactions D) All of the listed choices describe mechanisms used by enzymes to achieve their rate enhancement of reactions.

D) All of the listed choices describe mechanisms used by enzymes to achieve their rate enhancement of reactions.

As a result of its involvement in a reaction, an enzyme _____. A) loses energy B) permanently alters its shape. C) is used up D) is unchanged E) loses a phosphate group

D) is unchanged

Which of the following statements applies to metalloenzymes? A) Some metal ions assist in ATP binding. B) The metal does not bind at the catalytic site. C) Amino acid residues in the enzyme are never covalently linked to the metal ion. D) Many are oxido-reductases. E) A and D

E) A and D

Which of the following is a feature of allosteric regulation of enzyme activity? A) Allosteric enzymes often have multiple active sites. B) Ligand binding causes a conformation change in the enzyme. C) There is often a range of different effectors for a single enzyme. D) Cooperativity in substrate binding. E) All of the above

E) All of the above

Which of the following statement is FALSE? A) The free energy barrier in a chemical reaction must be overcome in order for products to form. B) An enzyme can increase a reaction rate by lowering the activation energy. C) An increase in temperature can result in an increased reaction rate. D) Lowering the free energy of the transition state can increase a reaction rate. E) At a given temperature and time all molecules in a solution or a sample will have the same energy.

E) At a given temperature and time all molecules in a solution or a sample will have the same energy.

Enzymes can accelerate reactions by: A) lowering the energy for activation. B) promoting the removal or addition of protons. C) correctly positioning a metal ion for catalysis. D) binding a substrate or substrates. E) all of the above.

E) all of the above.

In general, enzymes are what kinds of molecules? A) lipids B) minerals C) nucleic acids D) carbohydrates E) proteins

E) proteins

A mutation causing an amino acid change in an enzyme that affects the turnover number kcat will always affect the KM as well. A) True B) False

B) False