Podcast
Questions and Answers
What is the role of allosteric enzymes in metabolic pathways?
What is the role of allosteric enzymes in metabolic pathways?
- Inhibiting all reactions.
- Catalyzing the committed step. (correct)
- Catalyzing the rate-limiting step.
- Facilitating only the final steps.
Feedback inhibition in metabolic pathways involves the end product of the pathway activating an enzyme early in the pathway.
Feedback inhibition in metabolic pathways involves the end product of the pathway activating an enzyme early in the pathway.
False (B)
What term describes the phenomenon where the product of a metabolic pathway inhibits an enzyme earlier in the pathway?
What term describes the phenomenon where the product of a metabolic pathway inhibits an enzyme earlier in the pathway?
Feedback inhibition
Where does the pathway product bind on the enzyme to inhibit its activity in feedback inhibition?
Where does the pathway product bind on the enzyme to inhibit its activity in feedback inhibition?
Allosteric enzymes always follow Michaelis-Menten kinetics.
Allosteric enzymes always follow Michaelis-Menten kinetics.
According to the concerted model, all active sites must be in the ______ state.
According to the concerted model, all active sites must be in the ______ state.
Which of the following is true regarding the T and R states in the concerted model of allosteric enzymes?
Which of the following is true regarding the T and R states in the concerted model of allosteric enzymes?
In the concerted model, the enzyme fluctuates between two states: T (tense) and active.
In the concerted model, the enzyme fluctuates between two states: T (tense) and active.
What kind of effects can the sequential model account for?
What kind of effects can the sequential model account for?
What term is used to describe the phenomenon in allosteric enzymes where the velocity increases over a narrower range of substrate concentration, compared to Michaelis-Menten enzymes?
What term is used to describe the phenomenon in allosteric enzymes where the velocity increases over a narrower range of substrate concentration, compared to Michaelis-Menten enzymes?
Allosteric regulators modulate the equilibrium between the R and T states of an enzyme; activators stabilize the R state, while inhibitors stabilize the ________ state.
Allosteric regulators modulate the equilibrium between the R and T states of an enzyme; activators stabilize the R state, while inhibitors stabilize the ________ state.
Match the descriptions with the enzyme regulation types:
Match the descriptions with the enzyme regulation types:
What results from a mutation that leads to the loss of allosteric control (but without an effect on catalytic activity) in the purine nucleotide synthesis pathway?
What results from a mutation that leads to the loss of allosteric control (but without an effect on catalytic activity) in the purine nucleotide synthesis pathway?
The activity of most enzymes is not influenced by regulatory molecules.
The activity of most enzymes is not influenced by regulatory molecules.
The enzyme's active site becomes unavailable to the substrates when a regulatory molecule binds to a different site on the enzyme.
The enzyme's active site becomes unavailable to the substrates when a regulatory molecule binds to a different site on the enzyme.
Enzyme regulation through covalent interactions most commonly involves the addition of a ______ group.
Enzyme regulation through covalent interactions most commonly involves the addition of a ______ group.
Irreversible inhibitors are commonly used by cells to regulate enzyme activity.
Irreversible inhibitors are commonly used by cells to regulate enzyme activity.
Which of the following best describes suicide inhibition?
Which of the following best describes suicide inhibition?
What bacterial process does penicillin inhibit?
What bacterial process does penicillin inhibit?
Multiple substrate reactions are divided into what main two groups?
Multiple substrate reactions are divided into what main two groups?
In a sequential reaction, all products must leave the enzyme at the same time.
In a sequential reaction, all products must leave the enzyme at the same time.
In a double-displacement reaction, the enzyme is temporarily modified, forming what is known as a(n) ______ enzyme.
In a double-displacement reaction, the enzyme is temporarily modified, forming what is known as a(n) ______ enzyme.
What happens to the enzyme after the first catalytic step in a double-displacement reaction?
What happens to the enzyme after the first catalytic step in a double-displacement reaction?
Chymotrypsin hydrolysis takes place in two stages called?
Chymotrypsin hydrolysis takes place in two stages called?
Match the following:
Match the following:
In what stage is the acyl-enzyme formed?
In what stage is the acyl-enzyme formed?
In chymotrypsin mechanism, The steps in catalysis are explained by the slow formation of an acyl-enzyme
In chymotrypsin mechanism, The steps in catalysis are explained by the slow formation of an acyl-enzyme
In kinetics of chymotrypsin catalysis, Two stages are evident: a rapid ______ and a steady-state phase
In kinetics of chymotrypsin catalysis, Two stages are evident: a rapid ______ and a steady-state phase
Which stage happens first in the kinetics of chymotrypsin catalysis
Which stage happens first in the kinetics of chymotrypsin catalysis
What is a key characteristics of the 'burst phase' in the context of chymotrypsin catalysis kinetics?
What is a key characteristics of the 'burst phase' in the context of chymotrypsin catalysis kinetics?
Flashcards
Allosteric Enzymes
Allosteric Enzymes
Enzymes that catalyze the committed step of metabolic pathways and act as catalysts and information sensors.
Feedback Inhibition
Feedback Inhibition
A regulatory mechanism where the end product of a metabolic pathway inhibits an earlier enzyme in the pathway.
Allosteric Enzymes regulation
Allosteric Enzymes regulation
Enzymes that may be inhibited or stimulated by several regulatory molecules.
Allosteric Enzymes kinetics
Allosteric Enzymes kinetics
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Concerted Model
Concerted Model
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Regulator Molecules
Regulator Molecules
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Enzyme Activity Regulation
Enzyme Activity Regulation
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Competitive Inhibition
Competitive Inhibition
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Allosteric Regulation
Allosteric Regulation
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Phosphorylation
Phosphorylation
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Irreversible Inhibitors
Irreversible Inhibitors
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Sequential Reactions
Sequential Reactions
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Double-Displacement Reactions
Double-Displacement Reactions
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Covalent Catalysis of Chymotrypsin
Covalent Catalysis of Chymotrypsin
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Study Notes
- Bio 504 Biochemistry Lecture about Enzymes by Alexander Heyl
Topics Overview
- Enzyme basics
- Substrate-enzyme interaction
- Limits of enzymes
- Michaelis Menten
- Regulation of enzyme activity
Role of Enzymes
- Allosteric enzymes catalyze the committed step of metabolic pathways
- Michaelis-Menten enzymes facilitate the remaining steps
- The conversion of A to B is the committed step, because once this occurs, B is committed to being converted into F
Allosteric Enzymes
- Allosteric enzymes are catalysts and information sensors
- They display quaternary structure with multiple active sites and regulatory sites
- Can be inhibited or stimulated by several regulatory molecules
- Do not conform to Michaelis-Menten kinetics
- Display a sigmoidal relationship to substrate concentration
- The amount of F synthesized can be regulated by feedback inhibition
- Pathway product F inhibits enzyme e₁ by binding to a regulatory site on the enzyme that is distinct from the active site
Concerted Model
- Allosteric enzymes depend on alterations in quaternary structure
- The enzyme exists in two different quaternary structures, designated T(tense) and R (relaxed)
- T and R are in equilibrium, with T being the more stable state
- The R state is enzymatically more active than the T state
- All active sites must be in the same state
- The velocity increases over a narrower range of substrate concentration for an allosteric enzyme compared to a Michaelis–Menten enzyme, showing a threshold effect
- Allosteric regulators disrupt the R<->T equilibrium when they bind the enzyme
- Inhibitors stabilize the T state, while activators stabilize the R state
Regulation of Enzyme Activity
- Enzyme activity is controlled by regulators
- These include reversible inhibition, allosteric control, covalent interaction, and irreversible inhibition
- Allosteric enzymes are regulated by products of the pathway they control
- Allosteric enzymes may be inhibited or stimulated by several regulatory molecules
Enzyme Regulation
- Most enzymes are controlled by regulators via reversible inhibition and allosteric control
- Enzyme regulation includes non-covalent interactions, such as competitive inhibition and allosteric regulation activation or inhibition
- Enzyme regulation includes covalent interactions where the function of an enzyme is altered by a chemical change of its structure
- Phosphorylation is the most common modification of enzymes
Enzyme Inhibitors
- Irreversible inhibitors bind very tightly to enzymes, called suicide inhibition
- They bind mostly covalently to the active site
- Examples include nerve gases, e.g. Sarin, or pesticides, which interact with acetylcholinesterase
- They are not typically used by cells to regulate enzyme activity
- Penicillin irreversibly inactivates a key enzyme in bacterial cell-wall synthesis by reacting with the transpeptidase to form an inactive complex that is indefinitely stable.
Bisubstrate Reactions
- Most biochemical reactions include multiple substrates
- Multiple substrate reactions can be divided into two groups: sequential reactions and double-displacement reactions
- A sequential reaction involves the first substrate (NADH) binding to the enzyme, followed by the second substrate (pyruvate) to form a ternary complex of two substrates and the enzyme
- Catalysis then takes place, forming a ternary complex of two products and the enzyme
- The products subsequently leave sequentially
Double Displacement
- In double displacement, the first substrate (aspartate) binds, and the first catalytic step takes place, resulting in a substituted enzyme (E-NH3).
- The first product (oxaloacetate) then leaves, and the second substrate (α-ket glutarate) binds to the substituted enzyme.
- The second catalytic step takes place and the NH3 is transferred to the substrate to form the final product, glutamate, which departs the enzyme.
Covalent Catalysis of Chymotrypsin
- Hydrolysis by chymotrypsin takes place in two stages: acylation to form the acyl-enzyme intermediate, followed by deacylation to regenerate the free enzyme
- Catalysis involves rapid formation of an acyl-enzyme intermediate and a slower release of the acyl component to regenerate free enzyme
- Kinetics of chymotrypsin catalysis shows two stages: a rapid burst phase (pre-steady state) and a steady-state phase
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