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Candidates who are preparing for their CSIR UGC NET exam might in need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point of time, We at BYJU'S Exam Prep come up with short notes on Transport of Protein Across the Endoplasmic Reticulum, which comes under the Biochemistry section of the Life Science syllabus. It includes the most important concepts from the CSIR-NET exam perspective. This set of short notes for Biochemistry have been meticulously designed by our experienced subject-matter experts, in order to give you the most standard set of study materials to be focused upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them in the learning process and for their future. Here we are offering the best study notes that are reliable and can be used by the students during their preparations for the upcoming CSIR-NET 2021 exam.
Transport of Protein Across Endoplasmic Reticulum
Proteins synthesized by membrane-bound ribosomes translocate the ER membrane co-translationally.
- Some proteins, however, are translocated into the endoplasmic reticulum and after their synthesis has been completed.
- Synthesis of these protein begins on an unattached ribosome in the cytosol.
- Ribosome engaged in the synthesis of proteins are targeted to the endoplasmic reticulum by the signal sequence at the N-terminus of the growing polypeptide chain.
- N-terminal signal sequences are cleaved from the polypeptide chain during its transfer to the ER lumen.
Sabatini and Blobel first proposed the hypothesis known as Signal hypothesis in 1971.
- A signal recognition particle SRP, a cytosolic particle binds to the signal sequence of the nascent polypeptide chain, and the complex of SRP, nascent polypeptide, and a ribosome then binds to the alpha subunit of the SRP receptor in the ER membrane.
- SRP receptor contains two polypeptide subunits: a transmembrane beta subunit and a peripheral alpha subunit.
- SRP Binding to the signal sequence slows translation, a phenomenon termed as elongation arrest.
- The interaction of SRP and SRP receptors directs the SRP-ribosome complex to the translocon.
- In mammals, translocon is made up of three polypeptides called the Sec61 complex.
The driving force for uni-directional translocation of across the ER membrane is provided by a protein Complex called Sec63 Complex and a member of the hsp70 family of molecular chaperones known as BiP(BiP for binding protein). The ATP-driven cycle of BiP binding and release pulls the protein into the lumen. Cleavage of the signal sequence by signal peptidase releases the polypeptide in the ER lumen.
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