Ubiquitin is a small protein found in all eukaryotic cells, playing a crucial role in regulating various cellular processes. It is best known for its function in tagging other proteins for degradation, a process that helps maintain cellular health by removing damaged or unneeded proteins. This tagging occurs through a process called ubiquitination, where ubiquitin molecules attach to target proteins. The ubiquitin-proteasome system is essential for controlling protein levels and ensuring proper cellular function. Dysregulation of this system can lead to various diseases, including cancer and neurodegenerative disorders like Alzheimer's disease. Understanding ubiquitin's role is vital for developing potential therapeutic strategies.