The following results were obtained in early studies on the translation of secretory proteins. Based on what we now know of this process, explain the reason why each result was observed. 

(a) An in vitro translation system consisting only of mRNA and ribosomes resulted in secretory proteins that were larger than the identical protein when translated in a cell. 

(b) A similar system that also included microsomes produced secretory proteins that were identical in size to those found in a cell. 

(c) When the microsomes were added after in vitro translation, the synthesized proteins were again larger than those made in a cell.