The least-stable reaction intermediate Protein catalyst Site on the enzyme where catalysis takes place Reactant in an enzyme-catalyzed reaction Small vitamin-derived organic cofactors Change in enzyme structure Function of Enzyme plus cofactor A coenzyme or metal Enzyme minus its cofactor

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Explanation:

An enzyme is a biological substance(particularly protein) that catalyze a  chemical reaction in a cell. They have an active site to which a substrate molecule bind, thus forming an enzyme- substrate complex. Sometimes an enzyme has to change its shape slightly so that a substrate molecule can bind to it. This phenomenon is called induced fit.

Cofactors are non protein substances, such as metal ions that are required for the speed up the catalytic activity of an enzyme

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.

c is the correct answer hope this !