Ribosomes are the RNA-protein enzyme complexes that synthesize proteins. There are no ribosomes inside the lumen of the secretor
y 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.
A membrane is made of amphipathic molecules with the hydrophobic part pointing to the lumen and cytosol and the hydrophobic part (much bigger makes up most of the membrane) in the middle, the protein chains that are embedded in the membrane are thus mostly hydrophobic because the membrane is mostly hydrophobic and like likes like
