ENZYMES

An enzyme accelerates both forward and reverse reactions equally by lowering activation energy without changing the equilibrium point or free energy.

Non-allosteric enzymes follow Michaelis-Menten kinetics, where the plot of V₀ vs. [S] is a rectangular hyperbola: first-order at low [S] and zero-order at high [S].

The triad allows histidine to act as a powerful general base catalyst, abstracting a proton from the serine hydroxyl group to make it a nucleophile.

Irreversible inhibitors covalently modify essential residues or cofactors, leading to permanent enzyme inactivation.

High temperatures disrupt non-covalent bonds (e.g., hydrogen bonds) stabilizing protein structure, causing irreversible unfolding (denaturation) and loss of active site shape.

A competitive inhibitor competes for the active site, requiring higher substrate concentrations to reach Vmax, thus increasing apparent Km.

Compartmentalization separates catabolic and anabolic pathways to prevent futile cycles and concentrates reactants to increase reaction efficiency.

The discovery of ribozymes (RNA catalysts) disproved the long-held belief that all enzymes are proteins.

When substrate is in excess, the reaction rate is directly proportional to enzyme concentration because every additional enzyme molecule can contribute to the product formation rate.

Km is the substrate concentration at half of Vmax. A low Km indicates high affinity, requiring only a low concentration to reach effective catalytic rates.

The active site, a 3D cleft formed by folding, provides the unique chemical and physical environment responsible for an enzyme's power and specificity.

Ribozymes are biologically active RNA molecules that possess catalytic activity, proving that biocatalysis is not exclusively the domain of proteins.

An inactive apoenzyme becomes an active holoenzyme upon binding its required cofactor, a non-covalent, reversible process essential for regulation.

A competitive inhibitor binds directly to the active site. This inhibition is overcome by high substrate concentrations; Vmax remains unchanged but apparent Km increases.

Ligases catalyze the joining of two molecules with the concomitant hydrolysis of a high-energy phosphate bond, such as ATP.

Allosteric regulation involves binding to a regulatory site, which induces a conformational change transmitted to the active site, modifying its affinity or efficiency.

Carbonic anhydrase is so efficient that the rate-limiting step is the diffusion of the substrate into the active site.

Malonate is a structural analog of succinate and competes for the active site of succinate dehydrogenase, demonstrating competitive inhibition.

Higher temperatures increase molecular kinetic energy, leading to more frequent and forceful collisions that increase the chance of overcoming the activation energy barrier.