Enzymes and active sites

What childhood experience does the author describe involving enzymatic cleaner?

They wore contact lenses as a kid and had to use a weekly “enzymatic cleaner,” which caused painful burning for about fifteen minutes if accidentally placed in the eyes without rinsing.

What does “enzymatic” mean in the author's contact lens cleaner?

It means the cleaner contained one or more enzymes, proteins that catalyze specific chemical reactions that broke down the film of eye goo on the contacts.

Why did the enzymatic cleaner sting when it got in the author’s eyes?

Because the enzymes would also break down eye goo in the eye itself, not just on the contacts.

What is a catalyst?

A substance that speeds up a chemical reaction without being a reactant.

What are the catalysts for biochemical reactions in living organisms called?

Enzymes.

What molecules can act as enzymes besides proteins?

Some ribonucleic acid (RNA) molecules can act as enzymes.

What critical task do enzymes perform in chemical reactions?

They lower a reaction’s activation energy—the amount of energy required for the reaction to begin.

How do enzymes make chemical reactions occur more readily?

They bind to reactant molecules and hold them in a way that makes bond-breaking and bond-forming occur more easily.

What does a reaction coordinate diagram with and without a catalyst show?

It shows that the activation energy is lower with a catalyst, but the overall ∆G of the reaction remains unchanged.

Do enzymes change a reaction’s ∆G value?

No, they do not change whether a reaction is energy-releasing or energy-absorbing because they do not alter the free energy of reactants or products.

What do enzymes lower if not ∆G?

They lower the energy of the transition state—the unstable state molecules must pass through during reaction.

What is the transition state in a chemical reaction?

An unstable, high-energy state at the top of the reaction’s energy “hill.”

What are substrates?

Reactant molecules that an enzyme binds in order to catalyze a reaction.

What may happen to substrates in enzyme-catalyzed reactions?

A substrate may be broken into multiple products, or two substrates may join to form a larger molecule or exchange pieces.

What is the active site?

The part of the enzyme where the substrate binds and the catalytic action occurs.

What is formed when a substrate binds to an enzyme?

An enzyme–substrate complex.

What happens after the enzyme–substrate complex undergoes reaction?

The substrate is converted into products, forming an enzyme–products complex, and the products leave the active site.

What gives an enzyme’s active site its specific properties?

The amino acids that make up the active site and their positions in 3D space.

What characteristics can active-site amino acid side chains have?

They can be large or small, acidic or basic, hydrophilic or hydrophobic.

Why can an active site bind only specific substrates?

Because the arrangement of amino acids creates a unique size, shape, and chemical environment suited to particular molecules.

What environmental factors can affect enzyme function?

Temperature and pH.

How does temperature affect enzyme activity?

Higher temperature generally increases reaction rates, but temperatures outside the tolerable range can disrupt active-site bonds and reduce binding efficiency.

What happens to most animal enzymes above 40°C/104°F?

They may denature, losing their shape and activity.

How does pH affect enzyme function?

Changes in pH can disrupt acidic or basic amino acids in the active site, making substrate binding difficult; extreme pH values can cause denaturation.

What is induced fit?

A slight change in enzyme shape upon substrate binding, producing a tighter fit between enzyme and substrate.

How did scientists previously think enzymes and substrates interacted?

Through a lock-and-key model, where they fit together without shape change.

What are some ways enzymes lower activation energy?

By bringing substrates together in the correct orientation, creating a favorable environment in the active site (e.g., slightly acidic or non-polar), bending substrates to facilitate bond-breaking, or forming temporary covalent bonds with substrates.

What role can active-site residues play during catalysis?

They may temporarily form covalent bonds with substrate molecules as part of the reaction.

Why are covalent interactions between enzymes and substrates temporary?

Because enzymes return to their original state at the end of the reaction and are not permanently altered.

What happens to an enzyme after it catalyzes a reaction?

It releases the product(s) and is ready to catalyze another reaction