Question

i need help answering this question in full paragraph please . typed and not hand written

2. What is necessary in an enzyme's active site in order for a symmetric molecule to react asymmetrically with the enzyme? Please provide an example of this phenomenon using an enzyme from the citric acid cycle.

Answer 1

Ans. The set of amino acids found in the active site, along with their positions in 3D space, give the active site a very specific size, shape, and chemical behavior. Thus, an enzyme's active site is uniquely suited to bind to a particular target—the enzyme's substrate or substrates—and help them undergo a chemical reaction.

asymmetry results in different binding affinities for the ligands.

distribution of catalytic groups and substrate molecules at the active site relative to such binding feature.
Example of TCA enzyme. - Fumarate hydratase (fumarase), the ubiquitous citric acid cycle
enzyme, catalyzes the addition of D2O to fumarate to give (3R)-L-malate. the enzyme catalyzes
the removal of the 3R hydrogen. If at the active site the conformation of L- malate approximates to the structure of fumarate, the substrates being stretched
between two counter ions , then the overall stereochemistry of the elimination is anti. The basic and acidic catalytic groups on the enzyme must be
so positioned as to abstract the pro-3R hydrogen and protonate the -OR group.

Another citric acid cycle enzyme aconitate hydratase (aconitase)
catalyses additions of water to cis-aconitate 12 to give either citrate 11 or (2R,3S)­ isocitrate 13, and in both cases the addition apparently anti. Furthermore, an essentially quantitative transfer of hydrogen, though not of OH, occurs when citrate goes to isocitrate without the intervention of free aconitate.