text: question about  cell receptors? what chemical reason would explain the observation that peptide hormones act by binding to cell surface receptors while steroid hormones act by binding to cytosolic receptors?  this question counts as a test question..thank you it relates to the polarity of the ligands in question.  peptide hormones are normally charged (that is their r substituent groups have polar atoms or groups) whereas steroid hormones are nonpolar molecules.  the phospholipid membrane of a cell is permeable only to nonpolar molecules such as steroid hormones and it acts to keep the peptide hormones out because of their charge.  for this reason, the cell has developed surface receptors located outside of the cell for peptide hormones and cystolic receptors for the steroid hormones that have direct access into the cell.