MCQs

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.

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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).

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