Question 1

What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations?

Accepted Answer

A plot of the inverse of the initial velocities (1/V) against the inverse of the substrate concentrations (1/[S]) is known as a Lineweaver-Burk plot. This plot is used to determine the values of 1/Vmax (y-intercept) and 1/Km (x-intercept) for an enzyme-catalyzed reaction.

Question 2

The graph in Figure 3-34 illustrates the change in the rate of an enzyme-catalyzed reaction as the concentration of substrate is increased.Which of the values listed below is used to calculate the enzyme turnover number?  Figure 3-34

Accepted Answer

The enzyme turnover number (kcat) is defined as the maximum number of substrate molecules that can be converted to product by one enzyme molecule per unit time when the enzyme is saturated with substrate. It is calculated using the formula kcat = Vmax/[E], where [E] is the enzyme concentration. From the graph, we can see that Vmax is reached at the highest substrate concentration and that VS can be approximated as Vmax. Therefore, kcat can be calculated using the formula kcat = Vmax/[E] = VS/[E] = VS/(Et - ES), where Et is the total enzyme concentration and ES is the enzyme-substrate complex concentration at steady-state. This simplifies to kcat = VS/([E]t - [ES]). Since [ES] is negligible at high substrate concentrations, we can assume that [E]t is constant and the turnover number can be calculated as kcat = VS/[E]t, which corresponds to answer choice C.

Question 3

If proteins A and B have complementary surfaces, they may interact to form the dimeric complex AB.Which of the following is the correct way to calculate the equilibrium constant for the association between A and B?

Accepted Answer

The equilibrium constant for the association between A and B is correctly represented by both the formula K = [AB]/[A][B] (which directly reflects the definition of the equilibrium constant for a bimolecular reaction) and the detailed balance principle in option A, which, despite its unconventional notation, essentially describes the same relationship in terms of rate constants for the association (on) and dissociation (off) processes.

Question 4

Energy cannot be created or destroyed, but it can be converted into other types of energy.Cells harvest some of the potential energy in the chemical bonds of foodstuffs to generate stored chemical energy in the form of activated carrier molecules, which are often employed to join two molecules together in __________ reactions.

Accepted Answer

Condensation reactions involve the joining of two molecules by removing a molecule of water. Activated carrier molecules, such as ATP or NADPH, can provide the energy required for this reaction to occur. Therefore, energy from the chemical bonds of foodstuffs can be converted into activated carrier molecules which can be used to drive condensation reactions in cells.

Question 5

The maximum velocity (V_max) of an enzymatic reaction is an important piece of information regarding how the enzyme works.What series of measurements can be taken in order to infer the maximum velocity of an enzyme-catalyzed reaction?

Accepted Answer

The best choice would be to measure the rate of substrate consumption shortly after mixing the enzyme and substrate for several substrate concentrations, since this will provide a range of values for the rate of the enzymatic reaction at different concentrations of the substrate. The other options may provide useful information, but they may not directly give us the maximum velocity of the reaction. Option A may provide an estimate of the equilibrium constant, but it does not necessarily provide the maximum velocity of the reaction. Option B may give a rate of product formation, but in some cases this may not be proportional to the rate of substrate consumption. Option C may give a rate of substrate consumption at high enzyme concentrations, but this may not provide information regarding the maximum velocity of the reaction.

Question 6

When the polymer X-X-X ...is broken down into monomers, it is "phosphorylyzed" rather than hydrolyzed, in the following repeated reaction: X-X-X ...+ P ? X-P + X-X ...(reaction 1) Given the ?G° values of the reactions listed in Table 3-27, what is the expected ratio of X-phosphate (X-P) to free phosphate (P) at equilibrium for reaction 1? X-X-X ...+ H₂O ? X + X-X ...?G° = ?4.5 kcal/mole X + ATP ? X-P + ADP ?G° = ?2.8 kcal/mole ATP + H₂O ? ADP + P ?G° = ?7.3 kcal/mole Table 3-27

Accepted Answer

The answer of When the polymer X-X-X ...is broken down...

Question 7

The net distance a molecule travels through the cytosol via diffusion is relatively short in comparison with the total distance it may need to travel.This is because movement governed by diffusion alone is a __________ process that is most effective for the dispersion of small molecules over short distances.

Accepted Answer

Diffusion is a slow and random process that is most effective for the dispersion of small molecules over short distances.

Question 8

In the case of a simple conversion reaction such as X→Y, which value of ΔG° is associated with a larger concentration of X than Y at equilibrium? (Hint: How is ΔG° related to K?)

Accepted Answer

When ΔG° is positive, it indicates that the forward reaction (X→Y) is not favored thermodynamically, leading to a larger concentration of reactants (X) than products (Y) at equilibrium. This is because ΔG° is related to the equilibrium constant (K) by the equation ΔG° = -RTlnK, where a positive ΔG° corresponds to a K less than 1, meaning reactants are favored.

Question 9

The study of enzyme kinetics is usually performed with purified components and requires the characterization of several aspects of the reaction, including the rate of association with the substrate, the rate of catalysis, and

Accepted Answer

The study of enzyme kinetics includes the characterization of the regulation of enzyme activity in addition to the rate of association with the substrate and rate of catalysis. The other answer choices, while important in understanding enzymes, are not directly related to enzyme kinetics.

Question 10

The graph in Figure 3-34 illustrates the relationship between reaction rates and substrate concentration for an enzyme-catalyzed reaction.What does the K_m value indicate with respect to enzyme-substrate interactions? Figure 3-34

Accepted Answer

The K_m value, also known as the Michaelis constant (Km), represents the substrate concentration at which half of the enzyme's active sites are occupied. It is a measure of the enzyme-substrate binding affinity, indicating how well the enzyme can bind to the substrate. Higher values of Km indicate weaker binding affinity, while lower values indicate stronger binding affinity.

Question 11

The equilibrium constant for complex formation between molecules A and B will depend on their relative concentrations, as well as the rates at which the molecules associate and dissociate.The association rate will be larger than the dissociation rate when complex formation is favorable.The energy that drives this process is referred to as __________ energy.

Accepted Answer

The energy that drives the process of complex formation is referred to as binding energy.

Question 12

For the reaction Y→X at standard conditions with [Y] = 1 M and [X] = 1 M, ΔG is initially a large negative number.As the reaction proceeds, [Y] decreases and [X] increases until the system reaches equilibrium.How do the values of ΔG and ΔG° change as the reaction equilibrates?

Accepted Answer

As the reaction proceeds towards equilibrium, the change in free energy (ΔG) decreases because the concentrations of both reactants and products become more similar. However, the standard free energy (ΔG°) remains the same because it is a constant value that represents the free energy change of the reaction under standard conditions. Therefore, the best choice is A, where ΔG becomes less negative (approaching zero) and ΔG° stays the same.

Question 13

The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of __________ in a process called __________.

Accepted Answer

High-energy bonds are commonly found in molecules such as ATP, which can be hydrolyzed (split) by the addition of water to release energy. This process is known as hydrolysis, and it is a common way for cells to obtain energy from the breakdown of biomolecules. Choice A is incorrect because ATP is the molecule whose bonds are being broken, not the molecule being added to break the bonds. Choices C and D do not involve the specific type of bond and process described in the question.

Question 14

Protein E can bind to two different proteins, S and I.The binding reactions are described by the following equations and values: E + S → ES K_eq for ES = 10 E + I → EI K_eq for EI = 2 Given the equilibrium constant values, which one of the following statements is TRUE?

Accepted Answer

The equilibrium constant (K_eq) is higher for ES than for EI, indicating that E binds more tightly to S than to I, and thus the binding energy of the ES interaction is greater.

Question 15

Which of the following statements is FALSE for a favorable binding reaction?

Accepted Answer

In a favorable binding reaction, the free-energy change is negative, the complex dissociation rate is slower than the rate for component association, and the binding energy for the association is large and negative. However, the concentration of the complex is expected to be higher than the concentration of the unbound components, not lower.

Question 16

Isomerization of glucose 1-phosphate to glucose 6-phosphate is energetically favorable.At 37°C, ΔG° = −1.42 log₁₀K.What is the equilibrium constant for this reaction if ΔG° = −1.74 kcal/mole at 37°C?

Accepted Answer

The equilibrium constant (K) for a reaction can be calculated from the standard free energy change (ΔG°) using the equation ΔG° = -RTlnK, where R is the gas constant (1.987 cal/(mol·K)) and T is the temperature in Kelvin. At 37°C (which is 310.15K), and given ΔG° = -1.74 kcal/mole, converting kcal to cal (1 kcal = 1000 cal), ΔG° = -1740 cal/mole. Plugging these values into the equation gives K = e^(-ΔG°/RT) = e^(1740/(1.987*310.15)) ≈ 16.98.

Question 17

The small molecule cyclic AMP (cAMP) takes about 0.2 second to diffuse 10 μm, on average, in a cell.Suppose that cAMP is produced near the plasma membrane on one end of the cell; how long will it take for this cAMP to diffuse through the cytosol and reach the opposite end of a very large cell, on average? Assume that the cell is 200 μm in diameter.

Accepted Answer

The time it takes for cAMP to diffuse through the cytosol is proportional to the square of the distance it has to travel. Therefore, it will take 100 times longer to travel 100 μm than it does to travel 10 μm. So, it will take 100 x 0.2 = 20 seconds to travel 100 μm.

Question 18

The equilibrium constant (K) for the reaction Y→X can be expressed with respect to the concentrations of the reactant and product molecules.Which of the expressions below shows the correct relationship between K, [Y], and [X]?

Accepted Answer

For the reaction Y → X, the equilibrium constant K is defined as the concentration of the products divided by the concentration of the reactants when the reaction has reached equilibrium. Therefore, K = [X]/[Y].

Question 19

Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell.Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups.Which of the molecules below donates a chemical group rather than electrons?

Accepted Answer

ATP donates a phosphate group rather than electrons. FADH, NADH, and NADPH all donate high-energy electrons.

Question 20

The study of enzymes also includes an examination of how the activity is regulated.Molecules that can act as competitive inhibitors for a specific reaction are often similar in shape and size to the enzyme's substrate.Which variable or variables used to describe enzyme activity will remain the same in the presence and absence of a competitive inhibitor?

Accepted Answer

Competitive inhibitors do not affect the maximum velocity (Vmax) of the enzyme-catalyzed reaction because the effect of the inhibitor can be overcome by increasing the substrate concentration.

Quiz 3: Energy, Catalysis, and Biosynthesis

What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations?

The graph in Figure 3-34 illustrates the change in the rate of an enzyme-catalyzed reaction as the concentration of substrate is increased.Which of the values listed below is used to calculate the enzyme turnover number? Figure 3-34

If proteins A and B have complementary surfaces, they may interact to form the dimeric complex AB.Which of the following is the correct way to calculate the equilibrium constant for the association between A and B?

The maximum velocity (V_max) of an enzymatic reaction is an important piece of information regarding how the enzyme works.What series of measurements can be taken in order to infer the maximum velocity of an enzyme-catalyzed reaction?

In the case of a simple conversion reaction such as X→Y, which value of ΔG° is associated with a larger concentration of X than Y at equilibrium? (Hint: How is ΔG° related to K?)

The study of enzyme kinetics is usually performed with purified components and requires the characterization of several aspects of the reaction, including the rate of association with the substrate, the rate of catalysis, and

The graph in Figure 3-34 illustrates the relationship between reaction rates and substrate concentration for an enzyme-catalyzed reaction.What does the K_m value indicate with respect to enzyme-substrate interactions? Figure 3-34

For the reaction Y→X at standard conditions with [Y] = 1 M and [X] = 1 M, ΔG is initially a large negative number.As the reaction proceeds, [Y] decreases and [X] increases until the system reaches equilibrium.How do the values of ΔG and ΔG° change as the reaction equilibrates?

The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of in a process called .

Protein E can bind to two different proteins, S and I.The binding reactions are described by the following equations and values: E + S → ES K_eq for ES = 10 E + I → EI K_eq for EI = 2 Given the equilibrium constant values, which one of the following statements is TRUE?

Which of the following statements is FALSE for a favorable binding reaction?

Isomerization of glucose 1-phosphate to glucose 6-phosphate is energetically favorable.At 37°C, ΔG° = −1.42 log₁₀K.What is the equilibrium constant for this reaction if ΔG° = −1.74 kcal/mole at 37°C?

The equilibrium constant (K) for the reaction Y→X can be expressed with respect to the concentrations of the reactant and product molecules.Which of the expressions below shows the correct relationship between K, [Y], and [X]?

Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell.Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups.Which of the molecules below donates a chemical group rather than electrons?

Quiz 3: Energy, Catalysis, and Biosynthesis

What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations?

The graph in Figure 3-34 illustrates the change in the rate of an enzyme-catalyzed reaction as the concentration of substrate is increased.Which of the values listed below is used to calculate the enzyme turnover number? Figure 3-34

If proteins A and B have complementary surfaces, they may interact to form the dimeric complex AB.Which of the following is the correct way to calculate the equilibrium constant for the association between A and B?

The maximum velocity (Vmax) of an enzymatic reaction is an important piece of information regarding how the enzyme works.What series of measurements can be taken in order to infer the maximum velocity of an enzyme-catalyzed reaction?

In the case of a simple conversion reaction such as X→Y, which value of ΔG° is associated with a larger concentration of X than Y at equilibrium? (Hint: How is ΔG° related to K?)

The study of enzyme kinetics is usually performed with purified components and requires the characterization of several aspects of the reaction, including the rate of association with the substrate, the rate of catalysis, and

The graph in Figure 3-34 illustrates the relationship between reaction rates and substrate concentration for an enzyme-catalyzed reaction.What does the Km value indicate with respect to enzyme-substrate interactions? Figure 3-34

For the reaction Y→X at standard conditions with [Y] = 1 M and [X] = 1 M, ΔG is initially a large negative number.As the reaction proceeds, [Y] decreases and [X] increases until the system reaches equilibrium.How do the values of ΔG and ΔG° change as the reaction equilibrates?

The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of __________ in a process called __________.

Protein E can bind to two different proteins, S and I.The binding reactions are described by the following equations and values: E + S → ES Keq for ES = 10 E + I → EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is TRUE?

Which of the following statements is FALSE for a favorable binding reaction?

Isomerization of glucose 1-phosphate to glucose 6-phosphate is energetically favorable.At 37°C, ΔG° = −1.42 log10K.What is the equilibrium constant for this reaction if ΔG° = −1.74 kcal/mole at 37°C?

The equilibrium constant (K) for the reaction Y→X can be expressed with respect to the concentrations of the reactant and product molecules.Which of the expressions below shows the correct relationship between K, [Y], and [X]?

Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell.Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups.Which of the molecules below donates a chemical group rather than electrons?

The maximum velocity (V_max) of an enzymatic reaction is an important piece of information regarding how the enzyme works.What series of measurements can be taken in order to infer the maximum velocity of an enzyme-catalyzed reaction?

The graph in Figure 3-34 illustrates the relationship between reaction rates and substrate concentration for an enzyme-catalyzed reaction.What does the K_m value indicate with respect to enzyme-substrate interactions? Figure 3-34

The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of in a process called .

Protein E can bind to two different proteins, S and I.The binding reactions are described by the following equations and values: E + S → ES K_eq for ES = 10 E + I → EI K_eq for EI = 2 Given the equilibrium constant values, which one of the following statements is TRUE?

Isomerization of glucose 1-phosphate to glucose 6-phosphate is energetically favorable.At 37°C, ΔG° = −1.42 log₁₀K.What is the equilibrium constant for this reaction if ΔG° = −1.74 kcal/mole at 37°C?