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Questions and Answers
What effect does a competitive inhibitor have on the apparent $K_m$ of an enzyme?
What effect does a competitive inhibitor have on the apparent $K_m$ of an enzyme?
- Decreases it
- Increases it (correct)
- Does not alter it
- Inverts it
Non-competitive inhibitors alter the $V_{max}$ of an enzyme, but they do not alter the $K_m$.
Non-competitive inhibitors alter the $V_{max}$ of an enzyme, but they do not alter the $K_m$.
True (A)
What is the primary mechanism by which cyanide inhibits cytochrome c oxidase?
What is the primary mechanism by which cyanide inhibits cytochrome c oxidase?
interfering with electron transport
In allosteric enzymes, the sigmoidal response is a result of combining two Michaelis-Menten enzymes, one with a high $K_m$ that corresponds to the ______ state and one with a low $K_m$ for the R-state.
In allosteric enzymes, the sigmoidal response is a result of combining two Michaelis-Menten enzymes, one with a high $K_m$ that corresponds to the ______ state and one with a low $K_m$ for the R-state.
Which of the following is an example of an irreversible enzyme inhibitor?
Which of the following is an example of an irreversible enzyme inhibitor?
Allosteric enzymes always follow Michaelis-Menten kinetics.
Allosteric enzymes always follow Michaelis-Menten kinetics.
Name one mechanism by which enzyme activity is regulated.
Name one mechanism by which enzyme activity is regulated.
Addition or removal of ______ from Ser, Thr, Tyr, and His residues regulates enzymes by kinase and phosphatase regulatory enzymes.
Addition or removal of ______ from Ser, Thr, Tyr, and His residues regulates enzymes by kinase and phosphatase regulatory enzymes.
Match the type of enzyme regulation with the corresponding time frame:
Match the type of enzyme regulation with the corresponding time frame:
Which hormone increases the rate of synthesis of key enzymes involved in glucose metabolism (e.g., glucokinase)?
Which hormone increases the rate of synthesis of key enzymes involved in glucose metabolism (e.g., glucokinase)?
Competitive inhibitors bind to the enzyme at a location distinct from the active site.
Competitive inhibitors bind to the enzyme at a location distinct from the active site.
Give an example of a condition that leads to an increase in insulin production.
Give an example of a condition that leads to an increase in insulin production.
Allosteric enzymes are regulated by modulators that bind ______ to the active site.
Allosteric enzymes are regulated by modulators that bind ______ to the active site.
What is the effect of a positive allosteric modulator on enzyme activity?
What is the effect of a positive allosteric modulator on enzyme activity?
Phosphorylation of an enzyme always leads to activation of the enzyme.
Phosphorylation of an enzyme always leads to activation of the enzyme.
How does feedback inhibition regulate metabolic pathways?
How does feedback inhibition regulate metabolic pathways?
In enzyme kinetics, $V_{max}$ represents the ______ rate of reaction when the enzyme is saturated with substrate.
In enzyme kinetics, $V_{max}$ represents the ______ rate of reaction when the enzyme is saturated with substrate.
Which type of inhibitor binds to both the enzyme and the enzyme-substrate complex?
Which type of inhibitor binds to both the enzyme and the enzyme-substrate complex?
Allosteric enzymes display hyperbolic kinetics, similar to Michaelis-Menten enzymes.
Allosteric enzymes display hyperbolic kinetics, similar to Michaelis-Menten enzymes.
The Michaelis-Menten equation describes the relationship between initial reaction rate ($v_0$), substrate concentration ([S]), and the Michaelis constant ($K_m$), where $v_0 = (V_{max} [S]) / ([S] + ______)$.
The Michaelis-Menten equation describes the relationship between initial reaction rate ($v_0$), substrate concentration ([S]), and the Michaelis constant ($K_m$), where $v_0 = (V_{max} [S]) / ([S] + ______)$.
Flashcards
Enzyme inhibitor
Enzyme inhibitor
A substance that reduces the activity of an enzyme.
Competitive inhibitor
Competitive inhibitor
An inhibitor that binds to the same site as the substrate, blocking substrate binding.
Non-competitive inhibitor
Non-competitive inhibitor
An inhibitor that binds to a site other than the active site, affecting enzyme conformation and activity.
Reversible inhibition
Reversible inhibition
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Irreversible inhibition
Irreversible inhibition
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Allosteric regulation
Allosteric regulation
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Allosteric activator
Allosteric activator
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Allosteric inhibitor
Allosteric inhibitor
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Covalent modification
Covalent modification
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Phosphorylation
Phosphorylation
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Dephosphorylation
Dephosphorylation
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Study Notes
- Lecture covers the effects of competitive and non-competitive inhibitors on enzyme kinetic parameters, cooperativity, allosteric modulation, reversible/irreversible inhibition, and enzyme activity regulation
Enzyme Inhibition
- Km represents the concentration of substrate at half Vmax
Competitive Inhibitors
- Competitive inhibitors increase the apparent Km
- They do not alter Vmax
- Competitive inhibitors block the enzyme active site
Non-Competitive Inhibitors
- Non-competitive inhibitors decrease Vmax
- They do not alter Km
- Non-competitive inhibitors interfere with the catalytic mechanism
- Cyanide inhibits cytochrome c oxidase by interfering with the transport of electrons within the enzyme
Irreversible Enzyme Inhibitors
- Some examples: Acetylcholinesterase (AChE) inhibitors
- Irreversible inhibitors include organophosphates and insecticides like nerve agents (Novichok)
Allosteric Regulation
- Allosteric enzymes show a sigmoidal curve in reaction velocity vs concentration
- Michaelis-Menten enzymes show a hyperbolic curve
Allosteric Enzymes Kinetics
- These are usually multi-subunit enzymes
- They exhibit cooperative substrate binding
- Sigmoidal response results from combining two Michaelis-Menten enzymes
Allosteric Enzymes Modulators
- Activity is modulated by allosteric activators and inhibitors
- Allosteric enzymes allow feedback inhibition of metabolic pathways
Regulation of Enzyme Activity
- Mechanisms of enzyme activity regulation:
- Allosteric enzymes are a type of regulation
- Covalent modification by other enzymes such as phosphorylation by kinases or dephosphorylation by phosphatases
- Induction or repression of enzyme synthesis
Regulation by Covalent Modification
- Reversible addition or removal of phosphate from Ser, Thr, Tyr, His residues by kinase and phosphatase regulatory enzymes
- Phosphorylated enzymes can be active (MAPK kinase) or inactive (glycogen synthase)
Regulation of Enzyme Synthesis
- The hormone insulin, a small protein, regulates enzyme synthesis
- High blood glucose increases insulin production in the pancreas
- This increases the synthesis rate of key enzymes in glucose metabolism like glucokinase and phosphofructokinase pyruvate kinase
Regulation of Enzyme Activity Summary
- Substrate availability has an immediate effect
- Product inhibition also has an immediate effect
- Allosteric control mediated by end products provides immediate regulation
- Covalent modification by other enzymes allows regulation in immediate to minutes
- Synthesis or degradation, controlled by hormones or metabolites, takes hours to days
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