Tuesday 26 March 2019

cell biology - Life cycle of proteins


I try to get a picture of the life cycle of a protein (considered as a specific molecule).


This is how I can imagine it:





  1. After the cell is born a protein molecule is synthesized by gene expression for the very first time de novo. This happens at a specific point in time and in space, typically at an ribosome, which may be located anywhere inside the cell.




  2. From the location of its generation (combination or recombination, see below) the protein travels to its final destination, e.g. as an ion channel in the cell membrane. (But possibly it was already synthesized very close to its point of use.) Or it just floats around in the cytosol. (Possibly, it gathers some other biomolecules around it.)




  3. Whereever it arrives or not: the protein lives and works for some time.




  4. Eventually, it gets damaged (= looses small functional units), but gets repaired in situ. Continue with 3.





  5. Eventually, it gets marked by ubiquitin and destructed in a controlled manner. Continue with 7.




  6. Eventually, it decays spontaneously (= splits into some larger fragments).




  7. Its fragments are released (in case it was bound) and start again to float around in the cytosol.





  8. Eventually, its (or other proteins') fragments are recombined (at specific points in time and in space, possibly at "re-factories" comparable to the ribosome-"factories"). Continue with 2.




Is this rough picture of the life-cycle of a protein essentially correct?


If so: What is known about the time ranges in which these processes take place? Especially: How long is the effective life and working time of typical proteins? Are there proteins that live and work only for minutes or hours, and others that live for months or years? (Specific examples are welcome!)




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