Final answer:
After rNTP uptake and RNA exit channel formation, translation elongation resumes with polypeptide chains passing through the RER translocation channel, signal peptide cleavage, and polypeptide folding. mRNA is exported from the nucleus to the cytoplasm, where its stability is regulated before translation. RNA synthesis proceeds until termination signals are reached, and ribosomal subunits are assembled before exiting the nucleus.
Step-by-step explanation:
Following the uptake of ribonucleoside triphosphates (rNTPs) and the formation of RNA exit channels, several processes occur to ensure the correct translation and localization of proteins within a cell. Protein synthesis begins with the initiation of translation, followed by elongation, where polypeptide chains are formed and pass through a translocation channel in the Rough Endoplasmic Reticulum (RER) membrane.
Once a signal recognition particle (SRP) binds to the signal peptide, protein elongation halts until the SRP-ribosome complex locates the RER. Upon docking at the RER membrane, the SRP detaches, allowing translation elongation to resume. A signal peptidase in the RER membrane conducts co-translational cleavage of the signal peptide that remains in the membrane, while the elongating polypeptide begins to fold inside the RER.
In parallel, mRNA processing includes utilization of a 5' methyl guanosine cap and poly(A) tail for its export from the nucleus to the cytoplasm. The mRNA is transported through nuclear pores aided by a nuclear transport receptor and other associated proteins. Once in the cytoplasm, these mRNAs are stabilized by RNA-binding proteins and microRNAs, determining the mRNA's lifespan and thus the level of protein synthesis.
RNA synthesis starts with an ATP or GTP residue and continues until RNA polymerase encounters a termination signal, such as a rho-dependent termination factor in bacteria. In eukaryotes, pre-rRNAs bound to ribosomal proteins in the nucleolus begin to assemble both small and large ribosomal subunits, which eventually exit the nucleus to partake in the translation process in the cytoplasm.