ENZYMES

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.

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].

Group specificity means an enzyme acts on a family of structurally related substrates (like alcohols) due to shared functional groups.

Cofactors are non-protein components (metal ions or coenzymes) required for the activity of many enzymes, distinguishing simple from conjugated enzymes.

A coenzyme acts as a co-substrate; it binds, accepts a chemical group from one substrate, and transfers it to another, being regenerated in the process.

A non-competitive inhibitor binds to a separate site, forming a non-productive complex that lowers the concentration of functional enzyme, thus reducing Vmax.

In a coupled assay where enzyme Y and its substrates are in excess, the rate of product formation by Y is proportional to the rate at which X provides its substrate.

Bell-shaped pH-activity profiles often reflect the ionization of catalytic residues that must be in a specific protonation state to function as acid/base catalysts.

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

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

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

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

Activation of zymogens requires specific, irreversible proteolytic cleavage to remove a blocking peptide, allowing the protein to fold into its active conformation.

Once all substrate is consumed, adding more enzyme cannot generate more product, and the reaction rate plateaus due to substrate depletion.

The lock-and-key model proposes that the enzyme's active site (lock) is a rigid, pre-shaped template perfectly complementary to a specific substrate (key).