Question

What 3 things occur when a ribosome binds to the translocon (sec61)?

A) GTP hydrolysis, protein translocation, SRP release
B) Ribosome dissociation, SRP binding, signal sequence cleavage
C) Signal recognition, polypeptide elongation, translocation pore closure
D) SRP-R binding, signal peptide cleavage, protein folding

Answer 1

When a ribosome binds to the translocon, three significant events occur: GTP hydrolysis catalyzed by the elongation factor-G (EF-G), protein translocation through the ER membrane, and SRP release to allow translation to continue.

Step-by-step explanation:

When a ribosome binds to the translocon (Sec61) in the process of synthesizing a protein, three key events occur:

1. GTP hydrolysis, which is catalyzed by the translocase (elongation factor-G, EF-G), as the ribosome translocates along the mRNA.
2. Protein translocation through the translocation channel in the rough ER membrane, during which the growing polypeptide chain begins to fold with the help of the ribosome that destabilizes certain interactions preventing premature folding.
3. SRP release, after which the signal recognition particle detaches from the polypeptide, allowing translation to resume and the polypeptide to continue passing through the translocon and into the lumen of the rough ER.

This process is crucial for the correct localization and folding of proteins that are destined for secretion or for residence within the endomembrane system.