Question 1

Which of the following statements best describes the induced fit model of enzyme activity?

Accepted Answer

A) The binding of substrate depends on the conformation of the active site. 
B) The binding of an activator alters the conformation of the active site to bind products more tightly. 
C) The binding of substrate changes the conformation of the active site to bind substrate more tightly. 
D) The binding of a competitive inhibitor changes the shape of the active site so that it binds substrate less tightly.

Question 2

Which of the following types of reactions would decrease the entropy within a cell?

Accepted Answer

A) anabolic reactions 
B) hydrolysis 
C) catabolic reactions 
D) digestion

Question 3

Which of the following statements is true of enzymes?

Accepted Answer

A) Required nonprotein cofactors generally alter the substrate specificity of enzymes. 
B) Enzyme function is generally increased if the three-dimensional conformation of an enzyme is altered. 
C) Enzyme function is generally independent of physical and chemical environmental factors such as pH and temperature. 
D) Enzymes generally increase the rate of chemical reactions by lowering activation energy barriers.

Question 4

Living organisms increase in complexity as they grow,resulting in a decrease in the entropy of an organism.How does this relate to the second law of thermodynamics?

Accepted Answer

A) Living organisms do not obey the second law of thermodynamics,which states that entropy must increase with time. 
B) The complexity is actually associated with greater disorder than the level of disorder associated with the organism at early stages of development. 
C) As a consequence of growing,organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth. 
D) Living organisms are able to transform energy into entropy.

Question 5

The ∆G for a particular enzyme-catalyzed reaction is -20 kcal/mol.If the enzyme is removed,what will be the ∆G for the noncatalyzed reaction?

Accepted Answer

A) -40 kcal/mol 
B) -20 kcal/mol 
C) 0 kcal/mol 
D) +20 kcal/mol 
E) +40 kcal/mol

Question 6

The cellular process of synthesizing large molecules from smaller ones is defined as

Accepted Answer

A) catalysis. 
B) metabolism. 
C) anabolism. 
D) dehydration. 
E) catabolism.

Question 7

Figure 6.4
-Figure 6.4 illustrates various aspects of the free-energy change (ΔG)for the reaction A + B ↔ C + D.Which of the following changes in free-energy represents the overall ΔG for the reaction?

Accepted Answer

A) a 
B) b 
C) c 
D) d 
E) e

Question 8

Which of the following statements best describes the critical role that ATP plays in cellular metabolism?

Accepted Answer

A) The covalent bond on the terminal phosphate of ATP is particularly strong,so it releases extra energy when hydrolyzed. 
B) It is one of the four building nucleotides required for DNA synthesis. 
C) ATP hydrolysis provides the energy used to power exergonic reactions in the cell. 
D) ATP serves as an energy shuttle in the cell,coupling exergonic and endergonic reactions.

Question 9

A mutation results in an amino acid substitution at a site distant from the active site of an enzyme.How might this amino acid change alter the active site and substrate specificity of the enzyme?

Accepted Answer

A) by changing the optimum temperature for the enzyme 
B) by changing the intracellular location of the enzyme 
C) by changing the binding site for an allosteric regulator 
D) by changing the conformation of the enzyme

Question 10

In experimental tests of enzyme evolution,a gene encoding an enzyme was subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity.The resulting enzyme with altered substrate specificity had multiple amino acid changes.Where in the enzyme might these amino acid changes be located?

Accepted Answer

A) only in or near the active site 
B) only in the hydrophobic interior of the folded protein 
C) only on surface sites distant from the active site 
D) in or near the active site,in the hydrophobic interior,and/or at surface sites distant from the active site

Question 11

The activity of many cellular enzymes is regulated by activators and inhibitors.Enzyme activity is also regulated in eukaryotic cells by which of the following mechanisms?

Accepted Answer

A) compartmentalization and restricting enzymes to specific organelles or membranes 
B) limiting the availability of substrates 
C) changing the primary structure of enzymes 
D) secreting enzymes out of the cell

Question 12

Which of the following statements regarding enzymes is true?

Accepted Answer

A) Enzymes increase the rate of a reaction by making the reaction more exergonic. 
B) Enzymes increase the rate of a reaction by lowering the activation energy barrier. 
C) Enzymes increase the rate of a reaction by reducing the rate of reverse reactions. 
D) Enzymes change the equilibrium point of the reactions they catalyze.

Question 13

Which of the following is an example of cooperativity?

Accepted Answer

A) binding of an ATP molecule along with another substrate in an active site 
B) binding of a molecule to one subunit of an enzyme,which promotes faster binding to each of the other subunits of the enzyme 
C) the product of one enzyme in a metabolic pathway serving as the substrate for the next enzyme in the pathway 
D) binding of the end product of a metabolic pathway to the enzyme that catalyzes the first step in the pathway

Question 14

Which of the following metabolic processes can occur without a net influx of energy from some other process?

Accepted Answer

A) ADP + <IMG/>i → ATP + H2O 
B) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O 
C) 6 CO2 + 6 H2O → C6H12O6 + 6 O2 
D) amino acids → protein

Question 15

In addition to its critical role in cellular metabolism,ATP may also be described as which of the following?

Accepted Answer

A) a pentose sugar 
B) a DNA nucleotide 
C) an RNA nucleotide 
D) an amino acid with three phosphate groups attached

Question 16

Hydrolysis of ATP releases energy,which ultimately results in the production of ADP and inorganic phosphate.What is commonly the immediate fate of the phosphate released by ATP hydrolysis in the cell?

Accepted Answer

A) It is secreted as waste. 
B) It diffuses through an ion channel into the Golgi apparatus,where it modifies secreted proteins. 
C) It is attached to ADP to regenerate ATP. 
D) It is attached to a substrate to form a phosphorylated intermediate.

Question 17

A solution of starch at room temperature does not readily decompose to form a solution of glucose because

Accepted Answer

A) the starch solution has less free energy than a solution of glucose. 
B) the hydrolysis of starch to glucose is endergonic. 
C) the activation energy barrier for this reaction cannot easily be overcome at room temperature. 
D) starch hydrolysis is nonspontaneous.

Question 18

A mutation that alters a single amino acid in a region of the enzyme outside of the active site may result in which of the following consequences?

Accepted Answer

A) It may alter the ability of a competitive inhibitor to bind to the enzyme. 
B) It will generally inactivate the enzyme. 
C) It will generally change the substrate specificity of the enzyme. 
D) It may alter an allosteric site on the enzyme.

Question 19

Succinate dehydrogenase catalyzes the conversion of succinate to fumarate.The reaction is inhibited by malonic acid,which resembles succinate but cannot be acted upon by succinate dehydrogenase.Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid.The effect of malonic acid on the activity of succinate dehydrogenase suggests which of the following?

Accepted Answer

A) Malonic acid is a noncompetitive inhibitor. 
B) Malonic acid is a competitive inhibitor. 
C) Malonic acid blocks the binding of fumarate. 
D) Malonic acid is an allosteric regulator.

Question 20

-In Figure 6.2,why does the reaction rate plateau at higher reactant concentrations?

Accepted Answer

A) Feedback inhibition by the product occurs at high reactant concentrations. 
B) Most enzyme molecules are occupied by substrate at high reactant concentrations. 
C) The reaction nears equilibrium at high reactant concentrations. 
D) The activation energy for the reaction increases with reactant concentration.

Exam 6: An Introduction to Metabolism