Which statement correctly distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways?

a) protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.
b) protein kinases are involved in signal transduction in unicellular eukaryotes such as yeast. protein phosphatases are involved in signal transduction in multicellular eukaryotes.
c) protein kinases are more critical than protein phosphatases to signal transduction enzymes.

A) Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.

Explanation:

Protein kinases are enzymes that have the ability to modulate other enzymes (or some other proteins) by adding the phosphate group. This is known as phosphorilation process. As a result of structural change, protein can change its activity (phosphorilation usually increase the activity).

Phosphatases are enzymes with opposite function, they remove phosphate group from the protein causing different effect.