Why are the hydrophobic amino acid R-groups on the outside of the alpha helix integral protein?
Assuming you’re refering to a transmembrane bitopic alpha helix (we should really stop naming different helices “alpha”!) then the hydrophobic R-groups are on the outside of the transmembrane portion, i.e. they will favour the hydrophobic environment inside the plasma membrane. This is what helps locate the protein in the membrane. If it were all hydrophillic, then it would favour the intra/extracellular environment (which would rather fail as a transmembrane protein!) In reality the ribosome is actually connected to the ER/Golgi membrane and the protein is partially transcribed through the membrane, and partially outside it, leaving it fixed inside. All this happens on golgi vesicles which then exocytose onto the membrane, taking their transmembrane proteins with them.
