Protein kinase is an enzyme that protein kinase is an enzyme that activates or inactivates other proteins by adding a phosphate group to them functions as a second messenger molecule serves as a receptor for various signal molecules produces second messenger molecules

The best answer to the question: Protein kinase is an enzyme that:___, would be: Activates or inactivates other proteins by adding a phosphate group to them.

Explanation:

Proteins are constantly being produced by the human body not just because they are the basic units of our muscles, but also because they virtually perform all kinds of functions within the body. Essentially, it could be said that the human body functions thanks to these particular molecules.

When the body assembles proteins from its genetic material, it forms strains of aminoacids that initially are inactive and therefore non-functional. However, when the precursor of the final protein is added with phosphate groups from ATP, the protein assumes its active formation and is capable of carrying out its intended function. This process of phosphorilation, or adding a phosphate group to proteins, is the job of protein kinases in the body.