Lecture 19 Questions Lecture 19 Questions 1. Chemical signals that travel between cells are found only in vertebrates. Steroid hormones can control protein synthesis in their target cells.
Hormone diffuses through the lipid bilayer of the plasma membrane.
Hormone binds with a specific receptor molecule, which is a protein. These molecules are too large to enter cells. These molecules cannot readily pass across the lipid bilayer that forms the plasma membrane. These molecules have too large an electrical charge to cross the plasma membrane. The concentration of these hormones in the blood is so low that it takes too long for these molecules to diffuse into the cell.