Final answer:
Proteasomes degrade only ubiquitin-tagged proteins because the addition of an ubiquitin group marks a protein for degradation. One way to control gene expression is by altering the longevity of the protein through the ubiquitin-proteasome system.
Step-by-step explanation:
Proteasomes degrade only ubiquitin-tagged proteins because the addition of an ubiquitin group marks a protein for degradation. Ubiquitin acts as a flag indicating that the protein's lifespan is complete. These tagged proteins are then moved to the proteasome, an organelle that functions to remove and degrade proteins. One way to control gene expression is by altering the longevity of the protein through the ubiquitin-proteasome system.
Proteasomes degrade ubiquitin-tagged proteins by recognizing the ubiquitin tag and then unfolding the protein with ATP hydrolysis. The protein is digested into peptides within the proteasome, and these peptides are broken down into amino acids in the cytoplasm. The process is crucial for cellular regulation and the removal of damaged proteins.
Proteasomes are complex protein structures in cells responsible for degrading ubiquitin-tagged proteins. When a protein is marked for degradation, ubiquitin serves as a flag signaling that the protein's life span has ended. Ubiquitin is a small regulatory protein that can be attached to other proteins to label them for destruction. This process begins with enzymes known as ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligases (E3), with E3 controlling the specificity of protein degradation.
Once tagged by ubiquitin, the protein is recognized by a proteasome and subsequently unfolded and translocated into its core. This unfolding is powered by ATP hydrolysis. Inside the proteasome, the protein is digested into peptide fragments by proteolytic enzymes. These fragments are then released and further broken down into free amino acids in the cytoplasm.
The process of ubiquitin-mediated protein degradation is essential for various cellular functions, including control of gene expression, cell-cycle regulation, response to stress, and removal of damaged or misfolded proteins. The specificity and versatility of the process are underscored by the existence of many different ubiquitin-protein combinations, catering to the diverse array of proteins that require degradation.