CH 7 - Part 2

Flashcards to review key concepts about allosteric enzymes, their regulation, and structural properties.

What are allosteric enzymes?

Enzymes that control the flux of biochemical reactions in metabolic pathways.

Why are allosteric enzymes important for metabolic pathways?

Complex metabolic pathways are possible because of their regulatory properties.

What is the committed step in a metabolic pathway?

The conversion of A to B, which commits B to being converted into F.

What type of step in the metabolic pathway do allosteric enzymes catalyze?

Allosteric enzymes catalyze this step, while Michaelis-Menten enzymes facilitate the remaining steps.

What are the conditions of committed steps?

Irreversible under cellular conditions.

How is the amount of F synthesized regulated in a metabolic pathway?

Feedback inhibition.

How does the pathway product F inhibit enzyme e1?

It inhibits enzyme e1 by binding to a regulatory site on the enzyme that is distinct from the active site.

How do regulatory molecules affect allosteric enzymes?

They may be inhibited or stimulated by several regulatory molecules.

What type of relationship is displayed with the reaction velocity of allosteric enzymes?

A sigmoidal relationship to substrate concentration.

What quaternary structure do allosteric enzymes display?

Multiple active sites and regulatory sites.

What is one model that explains the kinetics of allosteric enzymes?

The concerted model.

According to the concerted model, what two different quaternary structures can the enzyme exist in?

T (tense) and R (relaxed).

What are the characteristics of the T state in the concerted model?

Less active, but more stable.

What are the characteristics of the R state in the concerted model?

Enzymatically more active, but less stable.

According to the concerted model, what is the state of active sites?

All active sites must be in the same state.

According to the concerted model, what happens with the binding of substrate to one active site?

Traps the other active sites in the R state.

What is the disruption of the T ⇌ R equilibrium by the binding of substrate which favors binding more substrate called?

Cooperativity.

How sensitive are allosteric enzymes to changes in substrate concentration near their KM values compared to Michaelis-Menten enzymes?

More sensitive to changes in substrate concentration near their KM values.

What is the increased sensitivity of allosteric enzymes near their KM values called?

The threshold effect.

What is the main idea of the sequential model for allosteric enzymes?

Subunits undergo sequential changes in structure.

What effect do allosteric regulators have on the R ⇌ T equilibrium?

They disrupt the R ⇌ T equilibrium when they bind the enzyme.

What state do inhibitors stabilize in the T ⇌ R equilibrium?

Stabilize the T state.

What state do activators stabilize in the T ⇌ R equilibrium?

Stabilize the R state.

What is the disruption of the T ⇌ R equilibrium by substrates called?

The homotropic effect.

What is the disruption of the T ⇌ R equilibrium by regulators called?

The heterotropic effect.