Matric Biology: Enzymes, questions with answers

Answer: D. Biological catalyst

Enzymes are biological catalysts that speed up biochemical reactions without being consumed.

Answer: C. It loses its shape

Denaturation destroys the enzyme's specific 3-D shape (active site), so it can no longer bind substrate.

Competitive inhibition occurs when a molecule with a shape similar to the normal substrate (a competitive inhibitor) competes with the substrate for binding to the enzyme's active site. When the inhibitor occupies the active site, the actual substrate cannot bind, so the enzyme's activity is reduced. Since the inhibitor and substrate compete for the same site, increasing the substrate concentration can overcome/reverse this type of inhibition by outcompeting the inhibitor for the active site.

Enzymes are biological catalysts, usually globular proteins, that speed up the rate of specific biochemical reactions in living organisms without being consumed or permanently changed themselves.
Characteristics: (1) Specificity — each enzyme acts on a specific substrate due to the exact shape of its active site. (2) Catalytic efficiency — enzymes speed up reactions enormously by lowering activation energy. (3) Sensitivity to temperature — activity increases up to an optimum temperature, then falls as the enzyme denatures. (4) Sensitivity to pH — each enzyme has an optimum pH; extremes of pH denature the enzyme. …

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In non-competitive inhibition, the inhibitor binds to a site on the enzyme other than the active site (called the allosteric site), not resembling the substrate. This binding changes the overall shape of the enzyme, including its active site, so the substrate can no longer bind properly (or the enzyme-substrate complex cannot form product) — reducing enzyme activity. Since it does not compete with the substrate for the active site, increasing substrate concentration does not reverse the inhibition.

As temperature rises towards an enzyme's optimum (often around 37 °C in humans), the rate of reaction increases because molecules move faster and collide more frequently with more energy. Beyond the optimum, the rate falls sharply because heat disrupts the bonds holding the enzyme's 3-D shape, denaturing it — the active site loses its shape and can no longer bind substrate, so activity drops to zero at high temperatures. At very low temperatures, enzyme activity is also low because molecules move slowly, though the enzyme is not denatured.

Cofactors are non-protein chemical components required by some enzymes to become catalytically active (the complete active enzyme with its cofactor is called a holoenzyme).
Types: (1) Inorganic cofactors (activators) — metal ions such as Mg²⁺, Zn²⁺, Fe²⁺; (2) Organic cofactors (coenzymes) — small organic molecules, often vitamin-derived, such as NAD⁺, FAD, Coenzyme A, which may be loosely bound (coenzymes) or tightly/permanently bound (prosthetic groups) to the enzyme.

(1) By bringing the reacting substrate molecules close together in the correct orientation at the active site. (2) By straining or distorting the substrate's bonds, making them easier to break. (3) By providing a favourable microenvironment (e.g. altering local pH or forming temporary bonds with the substrate) at the active site that stabilises the transition state.