Question

Using what you know about the structures of the amino acid side chains and the mechanisms presented in this chapter, which of the following amino acid side chain may play the following roles in an enzymatic mechanism: a. participate in proton transfer, b. act as a nucleophile

Answer 1

In enzymatic mechanisms, histidine can facilitate proton transfer, whereas serine or cysteine can act as nucleophiles due to their unique side chains.

Step-by-step explanation:

In enzymatic mechanisms, the roles of certain amino acids are critical due to their unique side chains. For proton transfer, amino acids with side chains that can donate or accept protons are essential. This includes histidine (His), which can facilitate proton transfer due to its imidazole ring capable of acting as an acid or a base. When it comes to acting as a nucleophile, amino acids such as serine (Ser) or cysteine (Cys), with their hydroxyl and thiol groups respectively, can form covalent bonds with substrate molecules, therefore participating in mechanisms like acyl substitution reactions.

For example, in the case of the pepsin enzyme, histidine and cysteine side chains are involved in the catalytic process. Asparagine is another example of an amino acid which acts as a base catalyst due to its amide functional group, as seen in acetyl-CoA substrate interactions.

Answer 2

a. participate in proton transfer - His

b. acts as a nucleophile - Ser

Step-by-step explanation:

Enzymes are regulated because they are proteins. They are categorize based on how they catalyze. Heat weakens and inactivates the enzymes because of non covalent interaction. His amino acid participate in proton transfer because it is able to act as an acid as well as a base while Ser amino acid can act as nucleophile.