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Endoplasmic Reticulum

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Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The endoplasmic reticulum is an organelle in which an array of cell functions takes place, notably including the production of proteins, steroids and lipids. Proteins are formed in ribosomes, found in the rough endoplasmic reticulum. Steroids and lipids are formed in the smooth endoplasmic reticulum.

In Biology, one of my favorite words to say is endoplasmic reticulum. It just rolls off your tongue nicely. Unfortunately, for such a nice word to say it's a really long word to write. So typically you'll see it abbreviated ER.

The endoplasmic reticulum, whose name means inside the fluid of the cell network, is just that. It's a network of tubes and sacs and membrane that go throughout the cell. Now there's two versions of the endoplasmic reticulum, the rough endoplasmic reticulum which is named that because it's covered with ribosomes, little bumps on the surface there that are involved in protein synthesis whereas the smooth ER doesn't have any of those ribosomes so its surface will be a lot smoother and the smooth ER is involved in making lipids and steroid molecules such as cholesterol, testosterone as well as making the fossil lipids that make up all the membranes of all the organelles or the plasma membrane or some membrane itself. Additionally in some cells of your body, they may be involved in the breakdown of some materials that would be called detoxification.

Let's take a look at the inside of the cell and see where the ER is. If you're trying to find the ER, you'll always be able to find it right next to the nucleus because part of its membrane is actually merged with the outer membrane of the nucleus. So if we zoom in on this, we can see here this green layer here is the nuclear envelop which has a double layer and the outer layer just becomes this folded over layer here. Now you'll see these ones have all these blue bumpy bits on them. That's the rough ER with its blue bumpy ribosomes and if you ran your finger along it, it would feel greasy and bumpy so you'd hear that grrr sound. So just think RER [IB] is the rough endoplasmic reticulum. While the smooth ER which is much smoother but still it feels greasy cause it's made up of all those fossil lipids which are kind of fat. If you ran your fingers over that, it would go [IB] the smooth endoplasmic reticulum or SER. And we can see here that the rough ER is directly attach because it's working in close coordination with the nucleus and the golgi apparatus. The nucleus give the messenger RNA instructions to the ribosomes that are sitting on the rough ER, they pump their proteins that they're synthesizing into the rough ER and then it sends it off to the golgi apparatus.

Over here, the smooth endoplasmic reticulum, it may not be directly hooked up to the nucleus like that although it's interior ultimately will connect somewhere to those rough ER interiors. And they just take in the materials that are coming in through the cell and it's sending off little sacs of membrane out to whatever part of the cell needs it, and there you go. The endoplasmic reticulum has two main parts, rough and smooth. Rough does proteins smooth does not.