Final answer:
Ubiquitination (option 1) is the process that marks a protein for degradation in proteasomes. It involves the addition of an ubiquitin group and is crucial for regulating protein lifespan and gene expression.
Step-by-step explanation:
The process that marks a protein for degradation in proteasomes is called ubiquitination. This modification involves the addition of an ubiquitin group to a protein, signaling that the protein's lifespan has ended. The protein is then targeted and moved to a proteasome, which is a complex dedicated to the degradation of proteins.
The sequence of events starts with the activation of ubiquitin by ATP hydrolysis, binding of this active ubiquitin to an ubiquitin-activating enzyme, followed by a transfer to an ubiquitin-conjugating enzyme, and ultimately the protein that is meant to be destroyed replaces the conjugating enzyme and gets tagged with ubiquitin.
This regulatory mechanism not only ensures the removal of proteins that are no longer needed or damaged but also plays a crucial role in controlling gene expression by altering protein longevity.