Biochem exam 2 multiple choice

1) The minimum amount of energy required to bring about a chemical reaction is called:

A) Activation energy

B) Enthalpy of reaction

C) Free energy

D) Standard free energy

E) Transition state

A

2) Which of the following is not a property of enzymes?

A) Capable of being regulated

B) Reaction rates high in comparison to uncatalyzed reaction

C) Highly specific

D) Side products of reactions are rare

E) All of the above are true

E

3) Consider the following reaction diagram. Which letter indicates the transition state?

A) A; B) B; C) C; D) D; E) E

C

4) In contrast to inorganic catalysts, enzymes have an intricately shaped surface called the __________.

A) Substrate

B) Cofactor

C) Active site

D) Apoenzyme

E) Holoenzyme

C

5) The lock and key model of enzyme activity proposes that each

A) Enzyme can react with only a single substrate

B) Enzyme has a cofactor that promotes the catalytic activity

C) Substrate has a specific cofactor that binds it to the enzyme

D) Enzyme binds a specific substrate because the active site and substrate have complementary structures.

E) Both A and B are correct

D

6) The synthesis of enzymes in response to changing metabolic needs is referred to as:

A) Enzyme induction

B) Allosteric regulation

C) Negative feedback

D) Zymogen activation

E) Cooperative binding

A

7) Which of the following is a coenzyme?

A) NADP+

B) Zn++

C) Cu++

D) Insulin

E) Oxytocin

A

8) Alcohol dehydrogenase without NAD+

is called a _______:

A) Apoenzyme

B) Holoenzyme

C) Substrate

D) Cofactor

E) Coenzyme

A

9) The term synthetase is included in which class of enzymes?

A) Ligases

B) Hydrolases

C) Transferases

D) Lyases

E) Isomerases

A

10) Which of the following is not a type of oxidoreductase?

A) Peroxidase

B) Hydroxylase

C) Reductase

D) Dehydrogenase

E) Peptidase

E

11) Which of the following classes of enzymes catalyze reactions involving the cleavage of bonds by the addition of water?

A) Transferase

B) Hydrolase

C) Lyase

D) Ligase

E) Isomerase

B

12) The steady state assumption states that if:

k1 = the rate constant for ES formation

k2 = the rate constant for ES dissociation

k3 = the rate constant for product formation

A) k2 is highly negligible compared with k3

B) The rate of formation of ES is equal to the rate of its degradation over the course of the reaction

C) The rate of formation of ES exceeds the rate of degradation over the course of the reaction

D) k3 is negligible when compared to k2

E) Product concentration at the beginning of the reaction is low

B

13) The expression of the Michaelis constant is equal to:

A) (K2 + K3)/K1

B) (K2 + K1)/K3

C) (K1 + K2)/K3

D) (K3 + K1) + K3

E) (K2/K1) + K3

Where

K1 = the rate constant for ES formation

K2 = the rate constant for ES dissociation

K3 = the rate constant for product formation

A

14) Specific activity is defined as

A) Enzyme concentration that converts 1 mole of substrate to product per minute.

B) Enzyme concentration that converts 1 mole of substrate to product per minute

C) The number of I.U. per mg of protein

D) The number of I. U. per gram of protein

E) Enzyme concentration that converts 1 mm of substrate to product per minute.

C

15) In the Lineweaver-Burk double reciprocal plot the slope is equal to _____.

A) 1/[S]

B) 1/V

C) Km/Vmax

D) 1/Vmax

E) -1/Km

C

16) In the Lineweaver-Burk double reciprocal plot the vertical intercept is equal to ____.

A) 1/[S]

B) 1/V

C) Km/Vmax

D) 1/Vmax

E) -1/Km

D

17) In the Lineweaver-Burk double reciprocal plot the horizontal intercept is equal to _________.

A) 1/[S]

B) 1/V

C) Km/Vmax

D) 1/Vmax

E) -1/Km

E

18) In competitive inhibition, increasing the concentration of substrate:

A) Decreases the overall rate of the reaction

B) Increases the overall rate of the reaction

C) Is without effect

D) The observed effect depends on the inhibitor

E) Competitive inhibitors do not affect the rate of the reaction

B

19) Which of the following amino acids is capable of acting as a general acid or general base at physiological pH?

A) Glycine

B) Histidine

C) Tyrosine

D) Tryptophan

E) Proline

B

20) Which of the following amino acids can participate in covalent catalysis?

A) Tryptophan

B) Alanine

C) Serine

D) Histidine

E) Both C and D are correct

E

21) Which of the following is a feature of transition metals that makes them efficient cofactors?

A) Have a high concentration of positive charge

B) Can act as a Lewis acid

C) Have directed valences

D) Can exist as a variety of valence states

E) All of the above are correct.

E

22) NADPH and NADH are coenzymes found in which class of enzymes?

A) Dehydrogenases

B) Ligases

C) Hydrolases

D) Transferases

E) Both C and D are correct

A

23) Which of the following is not present in the active site of alcohol dehydrogenase?

A) Zn++

B) Histidine

C) Cysteine

D) NAD+

E) Proline

E

24) Enzyme control is accomplished in which of the following ways?

A) Genetic control

B) Covalent modification

C) Allosteric regulation

D) Compartmentation

E) All of the above are correct

E

25) Zymogens are a feature of what type of enzymatic control?

A) Genetic control

B) Covalent modification

C) Allosteric regulation

D) Compartmentation

E) Both B and C are correct

B

26) Regulatory enzymes are a feature of what type of enzymatic control?

A) Genetic control

B) Covalent modification

C) Allosteric regulation

D) Compartmentation

E) Both B and C are correct

C

27) Positive cooperativity is a feature of what type of enzymatic control?

A) Genetic control

B) Covalent modification

C) Allosteric regulation

D) Compartmentation

E) Both B and C are correct

C

28) Segregation of biochemical pathways into different organelles in an example of which type of enzymatic regulation?

A) Genetic control

B) Covalent modification

C) Allosteric regulation

D) Compartmentation

E) Both B and C are correct

D

29) Catalysts are effective because they:

A) Decrease the rate of the reverse reaction

B) Stabilize the transition state

C) Decrease the activation energy of a reaction

D) Increase the energy released during a reaction

E) B and C

E

30) Enzymes act by _________.

A) Decreasing the energy of activation of a reaction

B) Increasing the energy of activation of a reaction

C) Raising the temperature of a reaction

D) Providing a surface to favorably orient the reactants

E) Both A and D are correct

E

31) Enzyme studies are best carried out:

A) In dilute aqueous solution

B) In highly concentrated solutions of the enzyme

C) In highly concentrated solutions of the substrate

D) In the presence of an inert crowding agent

E) In the presence of a membrane

D

32) Alcohol dehydrogenase is an example of which of the following classes of enzymes?

A) Oxidoreductases

B) Transferase

C) Hydrolase

D) Lyase

E) Isomerase

A

33) Which of the following is not an assumption of the law of mass action?

A) Forward reaction is linear

B) Reverse reaction is linear

C) System is homogenous

D) Interacting molecules move randomly and independently of each other

E) All are assumptions of the law of mass action

E

34) Metabolons are defined as:

A) Multifunction enzymes

B) Complexes that channel product molecules from one active site to another

C) Metabolic intermediates

D) Effector molecules

E) Rate of flow of metabolites from one point to another

B

35) Metabolic flux is best defined as a:

A) Lubrication enzyme that promotes the flow of reactants

B) Rate of flow of metabolites from one point to another in a pathway

C) Rate of a reaction

D) Promoter molecule

E) Both A and D are correct

B

36) An enzyme without it cofactor is called ________

A) Coenzyme

B) Apoenzyme

C) Holoenzyme

D) Noncatalytic

E) Isoenzyme

B

37) Which of the following amino acids cannot actively participate in a catalytic site?

A) Serine

B) Threonine

C) Tyrosine

D) Glycine

E) Glutamine

D

38) In addition to serine and aspartate which of the following amino acids is a member of the serine triad?

A) Threonine

B) Tyrosine

C) Glutamine

D) Histidine

E) Glycine

D

39) Which of the following is not an important metal in biological systems?

A) Na+

B) K+

C) Mg++

D) Cu++

E) Ba++

E

40) The major site of alcohol detoxification is

A) Intestine

B) Kidney

C) Pancreas

D) Liver

E) Stomach

D

41) The main enzyme used to detoxify alcohol in humans is

A) ADH1

B) ADH2

C) ADH3

D) ADH4

E) All of the above

A

42) Consider the following diagram. What constitutes the activation energy for the forward reaction?

A) C-A

B) C-E

C) E-A

D) C-B

E) E-D

A

43) Which of the following statements is not true of enzymes?

A) Increase the reaction rate

B) Obey the laws of thermodynamics

C) Catalyses the forward reaction only

D) Does not affect the position of equilibrium

E) Not consumed by the reaction

C

44) Hexokinase is an example of which class of enzymes?

A) Hydrolase

B) Lyase

C) Isomerase

D) Transferase

E) Ligase

D

45) Pyruvate carboxylase is an example of which class of enzymes?

A) Oxidoreductase

B) Transferase

C) Hydrolase

D) Ligase

E) Lyase

D