Tyrosine kinases are a type of enzyme that play a crucial role in cell signaling. They add a phosphate group to the amino acid tyrosine on proteins, which can activate or deactivate various cellular functions. This process is essential for regulating cell growth, division, and metabolism. There are two main classes of tyrosine kinases: receptor tyrosine kinases (RTKs) and non-receptor tyrosine kinases. RTKs are found on the cell surface and respond to external signals, while non-receptor tyrosine kinases operate within the cell. Dysregulation of tyrosine kinases is often linked to diseases, including cancer.