text: Proteins are not too large to enter and leave the cell, however, proteins must be broken down into amino acids to pass the gut wall and enter the blood stream.  This is probably what you heard, afterall if large proteins were passing the gut wall regularly people would have a lot of allergic reactions (the basis for not feeding infants younger than six months cows milk).  \n\nProteins that are transcribed in the cytosol are for use inside the cell.  Moving on, proteins that are manufactured on the RER (rough endoplasmic reticulum) are made for excretion from the cell.  These proteins are then modified in the Golgi Apparatus and then excreted by the cell via vesicles that fuse with the plasma membrane.  I mean think about it!  Do you really think we could survive without our cells being able to excrete large compounds from our cells.  For example, insulin is a protein that regulate glucose uptake by cells,  if our body wasn't able to excrete this protein from pancreatic cells we wouldn't be able to survive!\n\nHope this helps.