Enzymes and metabolic pathways

What is metabolism?

All chemical reactions in a cell.

What is a metabolic pathway?

A series of reactions in which products from one step become reactants for the next.

What is an anabolic reaction?

It builds larger molecules from smaller ones and requires energy.

What is a catabolic reaction?

It breaks larger molecules into smaller ones and generally releases energy overall.

Is building a protein from amino acids anabolic or catabolic?

Anabolic—it builds a molecule and requires energy.

Is breaking down glucose during cellular respiration anabolic or catabolic?

Catabolic—the overall process releases energy that can help produce ATP.

What is an enzyme?

A biological catalyst, usually a protein, that speeds a chemical reaction.

How do enzymes speed reactions?

They lower activation energy, the energy barrier needed to start a reaction.

Are enzymes used up in their reactions?

No. They can catalyze reactions repeatedly.

Do enzymes change whether a reaction requires or releases energy?

No. They lower the activation barrier without changing the reaction’s overall energy change.

What is a substrate?

A reactant that binds to an enzyme.

What is an active site?

The region where substrates bind and the enzyme catalyzes the reaction.

What is induced fit?

An enzyme changes shape slightly when its substrate binds, improving the catalytic arrangement.

In “A + B → C,” which substances are reactants and products?

A and B are reactants; C is the product. An enzyme may be written above the arrow.

What is competitive inhibition?

An inhibitor occupies the active site, competing with the substrate.

What is allosteric inhibition?

An inhibitor binds away from the active site, changing the enzyme’s shape and reducing activity.

What is an allosteric activator?

A molecule that binds away from the active site and increases enzyme activity.

What is feedback inhibition?

A pathway’s end product inhibits an earlier enzyme, slowing further production.

What is an inorganic enzyme helper, such as a nickel or magnesium ion?

A cofactor.

What is an organic enzyme helper, often derived from a vitamin?

A coenzyme.

How does temperature affect enzyme activity?

Warming usually increases activity up to an optimum; excessive heat can denature the enzyme.

How does pH affect enzyme activity?

It changes charges and interactions in the enzyme, which can affect substrate binding or cause denaturation.

In “A → B → C,” what happens if the enzyme converting B to C is removed?

B tends to accumulate and C production decreases, assuming no alternate pathway.

What can happen if more enzyme is added to a pathway step?

That step may run faster if enough substrate is available; another step may still limit the pathway.