30 Questions
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.
What is the role of regulatory enzymes in metabolic pathways?
Regulatory enzymes usually catalyze the rate-limiting step in the pathway, affecting the rate of the entire pathway.
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.
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.
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.
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.
Which type of enzyme inhibitor binds to a site other than the catalytic site, causing conformational changes that affect enzyme activity?
Allosteric inhibitor
What type of modification can regulate enzyme activity through the addition of a phosphate group?
Phosphorylation
Which process involves the activation of target proteins through reversible binding by monomeric G-proteins?
Allosteric activation
What type of regulation occurs when the end product of a pathway controls its own rate of synthesis?
Feedback regulation
How are some enzymes initially synthesized before being activated by proteolysis?
As inactive precursors
In what way can enzyme concentration be regulated?
Through changes in synthesis or degradation rates
Which type of inhibitor alters the intersection on the y-axis in Lineweaver-Burk plots?
Noncompetitive inhibitor
What type of inhibition occurs when an inhibitor binds to the enzyme and enzyme-substrate complex with the same affinity?
Noncompetitive inhibition
Which type of inhibition prevents enzymes from generating a product faster than it can be used?
Product inhibition
What is a mechanism through which enzyme regulation can be achieved?
Allosteric activation and inhibition
What can rapidly change an enzyme from an inactive form to an active conformation?
Allosteric activation
In which model is the path from low-affinity to high-affinity conformation preferred?
Sequential model
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
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
What does the Lineweaver–Burk transformation visually determine from a plot of 1/vi versus 1/S?
Km and Vmax
Which type of hexokinase has a low Km for glucose?
Hexokinase I in red blood cells
What is the role of hepatic glucokinase in glucose metabolism?
Promotes glucose storage as liver glycogen or fat when glucose is in excess supply
What is MODY, a rare genetic form of diabetes mellitus, caused by?
Mutations in a single gene affecting insulin secretion
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
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
What does Vmax represent in enzyme kinetics?
The maximum rate of reaction achievable by the enzyme
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
What type of plot is typically shown by GK (glucokinase) in comparison to hexokinase I?
Slightly sigmoidal
How do noncompetitive inhibitors affect enzyme activity?
They do not compete with a substrate for its binding site
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
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.
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