Which of the three is true for insulin receptors?
Signal recognition particle (SRP) receptor, also called docking protein, is a dimer composed of 2 different subunits that are associated exclusively with the rough ER in mammalian cells. The surface of the rough endoplasmic reticulum (often abbreviated RER or Rough ER) (also called granular endoplasmic reticulum) is studded with protein-manufacturing ribosomes giving it a "rough" appearance. so i don't think (3) is the right statement.
the insulin receptors is made up of two hormones, insulin and glucagon, are at the center of this signaling system. there is no such things as hydrophobic sequence in the middle of the protein i believe.
also, Insulin is a peptide hormone produced by beta cells of the pancreatic islets and and insulin receptors doesn't have an hydrophobic signal peptide. so i think (1) is the correct answer.
Edit :
https://en.wikipedia.org/wiki/Signal_recognition_particle_receptor
https://www.healthline.com/health/type-2-diabetes/insulin#Function1
www.news-medical.net/health/What-is-Insulin.aspx