Types of Hormones Steroid hormone Cell membrane (a Ribosome mRNA 基因表达学说 Nucleus mRNA Protein receptor DNA c) rmone-receplo complex a)a steroid hormone crosses a cell membrane and [b] combines with a protein receptor usually in the nucleus. (c The hormone- receptor complex activates messenger RNA (mRNA] synthesis. [d The mRNA leaves the nucleus and [e] guides protein synthesis基因表达学说