Take a moment and write out some rules on what makes an ER-resident stay in the ER, what makes a lysosomal protein reach the lysosome, a secreted protein the plasma membrane. What tags do you remember? Is there a default trafficking destination for proteins?
Ans. In the cytosol of a cell , a number of process goes on like synthesis of proteins , metabolic processes etc. Proteins are synthesized by rough endoplasmic reticulum for other cell organelles and plasma membrane. Protein is transported from RER to other organelles through nuclear pores , across membrane and transported in vesicles. There is a sorting signal molecule on the protein being synthesized to direct the protein to designate organelle where it is needed.Nuclear localization signal direct a protein from cytosol to nucleus. Proteins targeted to mitochondria has localization signal at N terminal .Proteins remains unfolded due to chaperone. Small protein diffuses while large use translocase to move. The proteins not assembled properly remains in ER by binding to chaperone proteins under folded properly.Yes there is a default trafficking designation for proteins.
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