What happens to newly synthesized proteins once they enter the lumen of the rough ER?

1. Ribosomes on the rough ER transfer their newly synthesized proteins into the lumen. 2. Inside the lumen those proteins undergo structural modifications. 3. The modifications named are folding and the acquisition of side chains. 4. Tagging with phosphate groups happens later, in the Golgi, so that answer moves the step to the wrong organelle. 5. In the RER lumen proteins are folded and given side chains. 6. Breaking a protein down into amino acids describes lysosomal digestion, so that answer points at the wrong organelle entirely. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 4 "Cell Structure", section 4.4 The Endomembrane System and Proteins_