chapter 13 section 3

Question 1

How do enzyme-catalyzed reactions differ from simple first-order reactions?

Answer 1

They show saturation kinetics: first-order at low [S], zero-order at high [S].

Question 2

What causes zero-order kinetics in enzyme-catalyzed reactions?

Question 3

What is the fundamental equation of enzyme kinetics

Answer 3

The Michaelis-Menten equation.

Question 4

What is assumed in Michaelis-Menten kinetics?

Answer 4

Formation of ES complex, and slower breakdown of ES to product.

Question 5

What does 𝐾𝑚 represent?

Answer 5

substrate concentration reaction velocity is half of Vmax; reflects enzyme’s affinity for substrate.

Question 6

What does a low 𝐾𝑚 mean

Answer 6

High enzyme-substrate affinity

Question 7

What is Vmax?

Answer 7

The maximum velocity when enzyme is saturated with substrate.

Question 8

What is Kcat

Answer 8

Turnover number—substrate molecules converted to product per enzyme per unit time.

Question 9

What is the Michaelis-Menten equation?

Answer 9

v=(Vmax[S])/([S]+Km)

Question 10

in Michaelis-Menten kinetics, what remains constant during much of the reaction?

Answer 10

The concentration of the ES complex.

Question 11

Why is Vmax never truly reached?

Answer 11

It would require every enzyme molecule to be bound to substrate

Question 12

How does the Michaelis-Menten equation combine kinetics?

Answer 12

First-order at low [S], zero-order at high [S].

Question 13

What shape does the Michaelis-Menten curve follow?

Answer 13

A rectangular hyperbola.

Question 14

What does 𝑘cat (turnover number) represent?

Answer 14

Substrate molecules converted to product per enzyme per unit time at saturation.

Question 15

How is 𝑘cat related to Vmax

Answer 15

kcat=Vmax/[Et]

Question 16

What does 𝑘cat/Km measure?

Answer 16

catalytic efficiency of an enzyme

Question 17

Why is 𝑘𝑐𝑎𝑡/Km called a “second-order rate constant”?

Answer 17

reflects enzyme performance at low [S]

Question 18

What is the upper limit of 𝑘𝑐𝑎𝑡/Km

Answer 18

The diffusion limit (rate at which E and S collide).

Question 19

What is the Lineweaver-Burk equation used for?

Answer 19

To linearize the Michaelis-Menten equation for easier determination of 𝐾𝑚 and 𝑉𝑚𝑎𝑥​

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Question 20

What does a Lineweaver-Burk plot graph?

Answer 20

1/v vs 1/[S], yielding a straight line.

Question 21

Why is the Hanes-Woolf plot often preferred?

Answer 21

It has smaller, more consistent errors compared to Lineweaver-Burk.

Question 22

How does pH affect enzyme activity?

Answer 22

By altering ionizable side chains, substrate groups, and enzyme structure.

Question 23

Why do enzymes have an optimal pH range?

Answer 23

Because pH affects substrate binding (Km), catalysis (Vmax), or both.

Question 24

How does temperature affect enzyme-catalyzed reaction rates?

Answer 24

Rates generally increase with temperature until enzymes begin denaturing.

Question 25

What is the typical effect of a 10°C temperature rise on enzyme rate?

Answer 25

Reaction rate roughly doubles if the enzyme remains stable.

Question 26

What is Q10 in enzymology?

Answer 26

The ratio of reaction rates at two temperatures 10°C apart (often ≈ 2).

Question 27

Why do enzymes lose activity above ~50–60°C?

Answer 27

Because proteins denature at high temperatures.