Ribosomes are the RNA-protein enzyme complexes that synthesize proteins. There are no ribosomes inside the lumen of the secretory pathway. Instead, secreted and membrane-bound proteins are synthesized in the cytosol, but have short stretches of amino acids called "signal sequences" that target the newly-forming proteins to a special channel in the membrane of the ER that enables the movement of the newly-forming proteins into the ER. This "translocation" ceases if a protein sequence is reached that will be embedded in the plasma membrane. Protein synthesis will proceed, and the membrane-spanning sequence will eventually be embedded in the ER membrane. Which of the following features would such a transmembrane amino acid sequence have?
A. The amino acids would have mostly hydrophobic side-chains.
B. The amino acids would have mostly hydrophilic side-chains.
C.There's no way to predict the relative number of hydrophobic and hydrophilic side-chains in transmembrane amino acid sequences.