Ch 9 pp 159-165

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Questions and Answers

What is the relationship between enzyme rate and substrate concentration?

Enzyme rate increases with increasing substrate concentration, but reaches a maximum velocity when the enzyme is saturated with substrate. (correct)

Enzyme rate decreases with increasing substrate concentration, reaching a minimum velocity when the enzyme is saturated with substrate.

Enzyme rate is inversely proportional to substrate concentration.

Enzyme rate remains constant regardless of substrate concentration.

What is the role of regulatory enzymes in metabolic pathways?

Regulatory enzymes catalyze the fastest step in the pathway, affecting the rate of the entire pathway.

Regulatory enzymes have no significant impact on the rate of the metabolic pathway.

Regulatory enzymes only regulate the initial steps of a metabolic pathway.

Regulatory enzymes usually catalyze the rate-limiting step in the pathway, affecting the rate of the entire pathway. (correct)

What does the Michaelis–Menten equation describe?

The relationship between initial velocity of a reaction, substrate concentration, maximum velocity, and the substrate concentration at which the initial velocity is half of the maximum velocity. (correct)

The relationship between enzyme activity and pH levels.

The relationship between enzyme rate and the concentration of enzyme inhibitors.

The relationship between enzyme concentration and substrate concentration.

What is the function of the regulatory enzyme in a metabolic pathway?

The regulatory enzyme controls the rate-limiting step in the pathway, thus influencing the rate of the entire pathway. Signup and view all the answers

How do changes in physiologic state, time of eating, environment, diet, or age affect enzyme rates?

They cause the rates of some enzymes to increase and those of others to decrease. Signup and view all the answers

What is the impact of substrate concentration on enzyme rate?

Enzyme rate increases with increasing substrate concentration, but reaches a maximum velocity when the enzyme is saturated with substrate. Signup and view all the answers

Which type of enzyme inhibitor binds to a site other than the catalytic site, causing conformational changes that affect enzyme activity?

Allosteric inhibitor Signup and view all the answers

What type of modification can regulate enzyme activity through the addition of a phosphate group?

Phosphorylation Signup and view all the answers

Which process involves the activation of target proteins through reversible binding by monomeric G-proteins?

Allosteric activation Signup and view all the answers

What type of regulation occurs when the end product of a pathway controls its own rate of synthesis?

Feedback regulation Signup and view all the answers

How are some enzymes initially synthesized before being activated by proteolysis?

As inactive precursors Signup and view all the answers

In what way can enzyme concentration be regulated?

Through changes in synthesis or degradation rates Signup and view all the answers

Which type of inhibitor alters the intersection on the y-axis in Lineweaver-Burk plots?

Noncompetitive inhibitor Signup and view all the answers

What type of inhibition occurs when an inhibitor binds to the enzyme and enzyme-substrate complex with the same affinity?

Noncompetitive inhibition Signup and view all the answers

Which type of inhibition prevents enzymes from generating a product faster than it can be used?

Product inhibition Signup and view all the answers

What is a mechanism through which enzyme regulation can be achieved?

Allosteric activation and inhibition Signup and view all the answers

What can rapidly change an enzyme from an inactive form to an active conformation?

Allosteric activation Signup and view all the answers

In which model is the path from low-affinity to high-affinity conformation preferred?

Sequential model Signup and view all the answers

What is the relationship between substrate concentration and enzyme velocity when the substrate concentration is below Km?

Enzyme velocity is most sensitive to changes in substrate concentration below its Km Signup and view all the answers

How is Km related to the dissociation constant, Kd?

Km is related to the dissociation constant, Kd, and a higher Km requires a higher substrate concentration to reach Vmax Signup and view all the answers

What does the Lineweaver–Burk transformation visually determine from a plot of 1/vi versus 1/S?

Km and Vmax Signup and view all the answers

Which type of hexokinase has a low Km for glucose?

Hexokinase I in red blood cells Signup and view all the answers

What is the role of hepatic glucokinase in glucose metabolism?

Promotes glucose storage as liver glycogen or fat when glucose is in excess supply Signup and view all the answers

What is MODY, a rare genetic form of diabetes mellitus, caused by?

Mutations in a single gene affecting insulin secretion Signup and view all the answers

In the Lineweaver-Burk transformation, when [S] is infinite, what value does 1/[S] equal to, and where does the line cross the ordinate (y-axis)?

1/[S] = 0, and the line crosses the ordinate at 1/v = 1/Vmax Signup and view all the answers

What is the slope of the line in the Lineweaver-Burk transformation, and what does it represent?

Km/Vmax, representing the Michaelis constant and maximum velocity Signup and view all the answers

What does Vmax represent in enzyme kinetics?

The maximum rate of reaction achievable by the enzyme Signup and view all the answers

How is Vmax often expressed, and is it dependent on enzyme concentration?

As product produced per minute per milligram of enzyme, and it is independent of enzyme concentration Signup and view all the answers

What type of plot is typically shown by GK (glucokinase) in comparison to hexokinase I?

Slightly sigmoidal Signup and view all the answers

How do noncompetitive inhibitors affect enzyme activity?

They do not compete with a substrate for its binding site Signup and view all the answers

Study Notes

Enzyme Kinetics and Inhibition

Lineweaver–Burk transformation converts Michaelis–Menten equation to a straight line of the form y = mx + b
When [S] is infinite, 1/[S] = 0, and the line crosses the ordinate (y-axis) at 1/v = 1/Vmax
The slope of the line is Km/Vmax and where the line intersects the abscissa (x-axis), 1/[S] = –1/Km
Rate of reaction is directly proportional to enzyme concentration
Vmax is often expressed as product produced per minute per milligram of enzyme and is independent of enzyme concentration
Comparison between hexokinase I and GK, with GK showing a slightly sigmoidal plot
Multisubstrate reactions affect the rate equation and apparent value of Km (Km,app) depends on the concentration of cosubstrate or product present
Equations for the initial velocity of an enzyme-catalyzed reaction provide useful parameters for describing or comparing enzymes
Michaelis–Menten model is inapplicable to multisubstrate enzymes and enzymes present in higher concentration than their substrates
Reversible inhibition within the active site can alter enzyme activity through compounds binding in the active site
Competitive inhibitors "compete" with a substrate for binding at the enzyme’s substrate-recognition site
Noncompetitive inhibitors do not compete with a substrate for its binding site, and uncompetitive inhibition is almost never encountered in medicine

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Test your knowledge of enzyme kinetics and inhibition with this quiz covering topics such as Lineweaver–Burk transformation, Michaelis–Menten equation, enzyme concentration, Vmax, multisubstrate reactions, and reversible inhibition. See how well you understand the concepts and applications of enzyme kinetics.