AS.020.305 Midterm: cell bio final study sheet (dragged) 11
Document Summary
Many*proteins*are*controlled*by*regulated*destruction: the activity of a ubiquitin ligase is turned on either by e3 phosphorylation or by an allosteric transition in an e3 protein caused by its binding to a specific small or large molecule. For example, the anaphase- promoting complex (apc) is a multi-subunit ubiquitin ligase that is activated by a cell-cycle-timed subunit addition at mitosis. One common way to create such a signal is to phosphorylate a specific site on a protein that unmasks a normally hidden degradation signal. Another way to unmask such a signal is by the regulated dissociation of a protein subunit. Finally, powerful degradation signals can be created by cleaving a single peptide bond, provided that this cleavage creates a new n-terminus that is recognized by a specific e3 as a destabilizing n-terminal residue! Apoptosis: apoptosis is a form of programmed cell death, cells dying by apoptosis undergo characteristic morphological changes. In some cases, cell death gets rid of uneccesary cells.
