ENZYMES

Turnover number represents the maximum number of chemical conversions of substrate molecules per second that a single catalytic site executes.

The complete, active enzyme (holoenzyme) consists of the protein part (apoenzyme) and a cofactor. Removing the cofactor leaves the inactive apoenzyme.

Feedback inhibition is a regulatory mechanism where the end product of a pathway inhibits an enzyme acting earlier, preventing overproduction.

Enzymes accelerate reactions by stabilizing the transition state and providing an alternative reaction pathway with a lower activation energy.

At saturating substrate concentrations, the reaction rate is limited by enzyme concentration. Increasing the amount of enzyme creates more active sites and increases Vmax.

Enzyme specificity results from the chemical complementarity between the active site and the substrate's transition state.

Km is a measure of an enzyme's affinity for its substrate, defined as the substrate concentration at which the reaction rate is one-half of the maximum velocity (Vmax).

Enzymes are biological catalysts that accelerate reactions by decreasing the activation energy. They do not provide energy, alter the equilibrium constant, or change the free energy change (ΔG) of the overall reaction.

The tertiary structure of an enzyme, which dictates the shape of the active site, is stabilized by hydrogen bonds, ionic interactions, hydrophobic interactions, van der Waals forces, and covalent disulfide bonds.

A prosthetic group is a non-protein unit that is covalently or very tightly bound to an apoenzyme, making it a permanent part of the functional holoenzyme.

The active site is a specific, flexible 3D pocket formed by a few amino acids that binds the substrate and catalyzes its conversion to product via weak interactions.

Enzymes lower activation energy by providing an alternative reaction pathway where specific R-groups orient and stress substrates, stabilizing the transition state.

Substrate binding is mediated by multiple weak, non-covalent forces which are reversible, essential for both binding and product release.

A coenzyme is a non-protein organic molecule that binds transiently to an apoenzyme, allowing it to be separated by dialysis, unlike a prosthetic group.

The Induced Fit model states the active site is not rigid; substrate binding induces a conformational change that properly positions catalytic groups for optimized catalysis.

At high substrate concentrations, all enzyme active sites are occupied. The reaction velocity reaches a maximum (Vmax), and further substrate addition cannot increase the rate.

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.