ENZYMES

A mutation in the small number of residues forming the active site would directly abolish enzyme function, unlike mutations in distant structural or surface regions.

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

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

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

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

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.

Absolute specificity means the enzyme acts on only one specific substrate, unlike group specificity which acts on substrates with a common functional group.

DNA polymerase catalyzes the template-directed addition of deoxynucleotides to a growing DNA chain.

Isoenzymes are multiple forms of an enzyme that catalyze the same reaction but differ in kinetic properties, allowing for tissue-specific metabolic tailoring.

Many coenzymes are vitamin derivatives, such as pyridoxal phosphate (vitamin B6) which is required for aminotransferases.

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.