Signal transduction is the process by which cells communicate with one another and respond to external stimuli. It involves the transmission of signals from the outside of a cell to the inside, leading to changes in cellular behavior or gene expression. This process is essential for many important cellular functions, such as growth, differentiation, and immune response. Signal transduction pathways involve a series of protein interactions and modifications that relay the signal from the cell surface to the nucleus. Understanding signal transduction is crucial for elucidating the mechanisms underlying diseases such as cancer, diabetes, and neurological disorders, and for developing targeted therapies.