A precursor protein is an inactive form of a protein that undergoes modifications to become active. These proteins are synthesized in cells and often require cleavage or other chemical changes to reach their functional state. For example, the proinsulin precursor is converted into active insulin through enzymatic processes. Precursor proteins play essential roles in various biological processes, including hormone production and cellular signaling. They are crucial in the synthesis of proteins like neurotransmitters and peptides, which are vital for communication between cells. Understanding precursor proteins helps researchers develop treatments for diseases related to protein misfolding or deficiencies.