Enzymes flashcards

5.1 Enzymes

Catalyst

A substance that increases the rate of a chemical reaction and is not changed by the reaction.

Enzyme

A protein that functions as a biological catalyst. Enzymes are involved in all metabolic reactions; without them these reactions would be too slow to sustain life.

Active site (Core description of enzyme action)

The region of an enzyme where the substrate fits. Its shape is complementary to the substrate, and the substrate is converted to products.

Effect of temperature on enzyme activity (Core)

Activity rises to an optimum, then falls. High temperatures denature the enzyme. At low temperatures the enzyme is slow but not denatured.

Denatured

The enzyme's shape, including its active site, has changed so the substrate no longer fits and it no longer works. Enzymes are never "killed".

An amylase reaction reaches its end point in 40 s. Rate using 1000 ÷ time?

1000 ÷ 40 = 25 arbitrary units. A shorter time means a faster rate.

Enzyme action in four steps (Extended)Extended

Substrate enters the active site (complementary shape) → enzyme-substrate complex forms → substrate converted to products → products leave; the enzyme is unchanged and reused.

Enzyme specificityExtended

Only a substrate with a shape complementary to the active site can fit and form an enzyme-substrate complex. E.g. starch cannot fit the active site of lipase.

Explain why rate increases with temperature up to the optimumExtended

Molecules gain kinetic energy and move faster, so there are more frequent effective collisions between enzyme and substrate, and more enzyme-substrate complexes form per second.

Explain the effect of pH away from the optimumExtended

The shape of the active site changes, so the substrate fits less well and fewer enzyme-substrate complexes form. At extreme pH the enzyme is denatured. (Kinetic energy belongs only in temperature answers.)