Question

Describe the molecular players and the distinct steps involved in the cotranslational translocation of an integral membrane protein with an N-terminal signal sequence and a stop-tranfer anchor sequence in the middle of the protein. What topology will the protein have on the plasma membrane?

Answer 1

Frist, when translation start it N terminal binds with srp which then binds with srp receptor and after which with the help of bio protein these polypeptide chain hi inside the ER.

THIS TYOE OF PROTEIN IS MAINLY TRANSMEMBRANE PROTEINS HAVE THEIR HYDROPHILIC N TERMINAL SEGMENT ON THE ENDOPLASMIC FACE AND HYDROPHILIC C TERMINAL SEGMENT IN THE CYTOSOLIC FACE.IT CONTAINS INTERNAL STOP TRANSFER SIGNAL and cleavable n terminal signal sequence .

When the chain enters the lumen of ENDOPLASMIC reticulum it's n terminal signal se6 is cleaved.a sequences of nonpolar amino acids in these protein acts as a stop transfer signal which stops the transfers of growing polypeptide chain.the internal sequences then becomes anchored in the lipid bilayers of the membrane.

Although , translocations is stop but translation is continuied at the ribosomes.

So when the c terminal amino acid is synthesized it loops out on the cytoplasmic side of the membrane .

This protein's n terminal sequence remain in the monocytosolic part and c terminal part on cytoplasmic side.

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