Question

Describe how newly translated proteins that are destined to enter the lumen of the ER are translocated across the membrane of the ER. (Can you please include some visuals to understand the process)

Answer 1

The newly translated proteins that are destined to enter the lumen of the ER are translocated by multiple process of signalling. The proteins during translation enter the ER in presence of a signal peptide. In order for them to enter the ER, the proteins need to bind to organelles of endomembrane system. The signal peptide is recognised by signal-recognition particle (SRP) which helps in sending the protein into the ER during the translation process. The SRP brings the ribosome to the ER as it binds to ER surface receptors. The ribosome continues to translare as the polypeptide is fed through the pore into the ER lumen. The signal peptidase breaks the signal peptide and the amino acid chain or newly synthesized protein slides into the ER Lumen. The completed polypeptide then is released into ER lumen where it floats freely.