In: Biology
Predict where the proteins with the following features end up in a cell. Explain your answer:
a) N-terminal ER targeting sequence, a cleavable signal sequence and a stop transfer sequence.
b) N-terminal ER targeting sequence, and a cleavable signal sequence.
A signal sequence is a targetting sequence that allows protein translocation to a specific organelle of the cell. An ER tageting sequence is present in both which means that the protein will be targetted to the ER. This signal sequence is usually present in the N terminal and is cleavable meaning that it will be cleaved by intercellular proteases when the protein is translocated to the ER. Protein will then move into the lumen of the ER. Again presence of a stop transfer sequence stops the translocation of the protein. Protein translocation into ER is guided by many proteins like SRP - Sec 61 complex, Sec A complex etc and they can recognise the signal seq or the stop transfer seq. When a stop transfer seq is recognised translocation to the lumen is immediately stopped and the protein gets halted in the membrane of the ER. So according to the given data, the proteins are:
a. ER transmembrane protein found lodged in the membrane of ER.
a. ER resident protein found in the lumen.
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