Final answer:
Ubiquitin is transferred to proteins tagged for degradation by ubiquitin-activating enzyme (E1), followed by ubiquitin-conjugating enzyme (E2) and finally ubiquitin ligase (E3), which signal the protein for destruction in the proteasome.
Step-by-step explanation:
In the process of protein degradation, ubiquitin is transferred by a series of enzymes to proteins destined to be broken down. Ubiquitin-activating enzyme (E1) initiates the process by binding with ubiquitin in an ATP-dependent manner. Subsequently, an ubiquitin-conjugating enzyme (E2) takes over from E1, and finally, the target protein gets replaced by ubiquitin ligase (E3), which facilitates the transfer of ubiquitin to the target protein, signalling it for destruction. The tagged protein is then led to the proteasome where, through ATP hydrolysis, it is unfolded and digested into small peptides and eventually into amino acids. This process is crucial for maintaining cellular health by controlling the quality of proteins and regulating gene expression through the degradation of specific proteins