Dynamic Catalysis: Enzyme Kinetics and Mechanisms Quiz

Enzymes act as biological catalysts by providing an alternative reaction pathway with a lower activation energy. By stabilizing the transition state, they allow more substrate molecules to reach the energy threshold required for the reaction to proceed at physiological temperatures.

The Michaelis constant Km is the substrate concentration at which the reaction velocity is half of Vmax. A low Km value indicates high affinity, meaning the enzyme can reach half maximum velocity even at low substrate concentrations, whereas a high Km suggests weaker binding.

This is false. At saturation, all available enzyme active sites are occupied by substrate molecules. The reaction reaches its maximum velocity Vmax, and further increases in substrate concentration cannot speed up the reaction because the enzyme is working at its full capacity.

Enzymes use various chemical strategies. Acid base catalysis involves proton transfer. Covalent catalysis forms a temporary bond between enzyme and substrate. Metal ion catalysis uses ions to orient substrates or stabilize charges. These interactions are precisely arranged within the active site to facilitate bond breaking and forming.

The Induced Fit model proposes that the enzyme is flexible. When the substrate enters the active site, the enzyme changes its shape slightly to bind the substrate more snugly, placing chemical strain on the substrate bonds to facilitate the reaction.

The Lineweaver Burk plot turns the Michaelis Menten equation into a straight line. The y intercept represents 1 divided by Vmax, while the x intercept represents negative 1 divided by Km. This plot is particularly useful for distinguishing between different types of enzyme inhibition.

This is false. Competitive inhibitors resemble the substrate and compete directly for the active site. This increases the apparent Km meaning lower affinity but does not change Vmax because the inhibition can be overcome by adding more substrate.

Non competitive inhibitors bind to an allosteric site, changing the enzyme shape and reducing its catalytic efficiency. This lowers the Vmax because the enzyme cannot function as effectively regardless of substrate concentration. However, it does not interfere with substrate binding, so Km remains unchanged.

Temperature, pH, and salinity affect the non covalent interactions like hydrogen bonds and ionic attractions that maintain an enzyme 3D shape. If the active site is distorted, the enzyme cannot bind the substrate properly. Substrate concentration affects the rate but does not alter the physical structure of the enzyme itself.

Many enzymes require cofactors like magnesium ions or coenzymes like vitamins to function. The protein part alone is called an apoenzyme, and the fully functional enzyme with its cofactor is called a holoenzyme.

This is true. The transition state is the peak of the energy barrier in a reaction. Enzymes stabilize this state, reducing the energy difference between the reactants and the transition state, which is the definition of lowering activation energy.

High thermal energy disrupts the weak forces holding the enzyme complex 3D shape together. Once the enzyme denatures, the specific geometry of the active site is lost, rendering the catalyst non functional.

The active site is a relatively small region of the total enzyme, composed of amino acids that may be far apart in the primary sequence but are brought together by 3D folding. Its specific shape and chemical environment ensure that only specific substrates can bind.

The turnover number measures the maximum catalytic activity of a single enzyme molecule. It represents the number of substrate molecules turned over into product by one active site per second when the enzyme is fully saturated.

This is true. Allosteric enzymes typically have multiple subunits and exhibit cooperativity, where the binding of a substrate to one active site affects the others. This results in an S shaped curve, allowing the enzyme to be highly sensitive to small changes in substrate concentration.