So a polypeptide that is destined for secretion or to be inside the cell membrane contains a special sequence of amino acids beginning at the beginning of that growing polypeptide chain, at the end terminus. And as soon as the ribosome synthesizes the signal sequence, a group of molecules known as the signal recognition particles, or SRP, can recognize that sequence. So as soon as the signal sequence is synthesized by the free ribosomes, the signal recognition particles, the complex of proteins and RNA molecules, binds to the signal sequence and moves the ribosome to the er membrane. Now, how exactly does the binding between the SRP ribosome complex and the membrane of our endoplasmic reticulum actually take place? So let's take a look at our Er membrane. So, this is the phospholipid bilayer of the Er membrane.