QCM : Enzyme Function and Regulation — 10 questions

Explication

The induced fit model of enzyme action was proposed by Daniel Koshland in 1958. It describes how enzyme flexibility allows the enzyme to change shape upon substrate binding, enhancing catalytic efficiency. The other options are well-known scientists but are associated with different discoveries: Pauling with chemical bonding, Pasteur with germ theory, and Koch with germ identification.

Explication

The lock-and-key model was first proposed by Emil Fischer in 1894, describing enzyme specificity based on complementary shapes between enzyme and substrate. The other dates correspond to the proposal of the induced fit model (1958), a later development, or are unrelated.

Explication

Enzymes are proteins that function as biological catalysts, increasing the rate of biochemical reactions without being consumed or permanently altered, which is fundamental to their role in cells.

Explication

The induced fit model describes enzymes as flexible molecules that undergo conformational changes upon substrate binding, leading to a better fit and more efficient catalysis. This flexibility is a key property that distinguishes it from the lock-and-key model, which assumes a rigid enzyme structure.

Explication

The enzyme described transfers a methyl group from S-adenosylmethionine to a substrate, which is characteristic of transferases. Transferases facilitate the transfer of functional groups between molecules, and methyl transfer is a common subclass of transferases, often called methyltransferases. The other options are incorrect as oxidoreductases transfer electrons, hydrolases catalyze hydrolysis, and lyases cleave bonds without hydrolysis or oxidation.

Explication

Oxidoreductases are enzymes that catalyze oxidation-reduction (redox) reactions, transferring electrons between molecules, whereas transferases catalyze the transfer of functional groups from one molecule to another. This distinction makes option 0 correct, as it accurately describes their different catalytic roles.

Explication

Enzymes facilitate reactions primarily by stabilizing the transition state, which lowers the activation energy required for the reaction. This reduction in activation energy results in an increased reaction rate. The stabilization does not increase activation energy or affect the thermodynamic favorability; rather, it makes the pathway to the product more accessible. Enzymes are not consumed in the reaction, so they are not destroyed or used up.

Explication

pH and temperature are crucial for maintaining the proper three-dimensional structure of enzymes, which is necessary for their activity. Deviations from optimal conditions can lead to denaturation or decreased activity, making their role primarily to influence enzyme stability and conformation.

Explication

Leonor Michaelis, along with Maud Menten, proposed the Michaelis-Menten kinetics model, which provides the foundation for understanding enzyme behavior, including how inhibitors affect enzyme activity. The other scientists made significant contributions to biochemistry but are not credited with proposing enzyme inhibition mechanisms.

Explication

Coenzymes are organic molecules that are derived from vitamins, which help enzymes carry out their catalytic functions. This distinguishes them from inorganic cofactors like metal ions.