We have the rough endoplasmic reticulum that contains these dots, and this smooth endoplasmic reticulum, shown in region five that lacks those dots. So the endoplasmic reticulum, right next to our nucleus contains ribosomes embedded in our membrane of that Er. And this gives it a granular appearance under the microscope. And that's exactly why we call it the rough Er, because it contains those ribosomes inside the membrane of the Er. Now, what exactly is the function, the purpose of our Er? So basically the Er, the rough endoplasmic reticulum, functions to synthesize our proteins.