ENZYMES

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).

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.

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.

Unlike inorganic catalysts, enzymes are highly specific and their activity is finely regulated by cellular mechanisms like allosteric control.

By lowering the activation energy, enzymes allow a much larger proportion of substrate molecules to reach the transition state at a given temperature, increasing the reaction rate.

The protein portion alone is the inactive apoenzyme, which requires a non-protein cofactor to form the complete, active holoenzyme.

Enzyme specificity arises from the unique 3D structure of the active site, which contains amino acid R-groups positioned to form interactions only with a specific substrate.

The induced fit model is exemplified by conformational changes in hexokinase upon glucose binding, which correctly orient ATP for catalysis.

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.