Protein phosphorylation is a biochemical process where a phosphate group is added to a protein molecule. This modification typically occurs on specific amino acids, such as serine, threonine, or tyrosine. Phosphorylation can change the protein's function, activity, or location within the cell, playing a crucial role in regulating various cellular processes. The addition of the phosphate group is usually catalyzed by enzymes called kinases, while the removal of the phosphate group is performed by phosphatases. This dynamic process is essential for many cellular functions, including cell signaling, metabolism, and cell division, making it a key mechanism in cellular regulation.