In this video, we're going to talk about the 2nd organelle of the endomembrane system, which is the endoplasmic reticulum. The endoplasmic reticulum is commonly abbreviated with the letters ER, and you'll see this abbreviation ER throughout our lesson moving forward a lot. The endoplasmic reticulum, or the ER, once again is a part of the endomembrane system which means that the endoplasmic reticulum is a membranous structure whose border is made of a membrane, and the endoplasmic reticulum, or the ER, is actually a membranous structure that is continuous with the nuclear envelope, which you might recall from some of our previous lesson videos, is really just another membrane structure that makes up the perimeter of the nucleus. The endoplasmic reticulum, or the ER, is an extension of the nucleus since it is continuous with the nuclear envelope.
Now, the endoplasmic reticulum, or the ER, actually has multiple functions, and we'll get to talk about some of those functions down below in our lesson. Again, the endoplasmic reticulum, or the ER, is a membranous structure whose border is made of a membrane, and that membrane serves as a barrier to separate the outside of the endoplasmic reticulum from the inside of the endoplasmic reticulum, and scientists refer to the inside of the endoplasmic reticulum as the ER lumen. The ER lumen can be defined as the internal space or compartment of the ER.
Now, there are actually 2 main types of endoplasmic reticulum that you should be familiar with, and we have those numbered down below: number 1 and number 2. The first type of endoplasmic reticulum that you should be aware of is the rough endoplasmic reticulum, or the rough ER, and the rough ER is commonly abbreviated as the RER for short. The rough endoplasmic reticulum is actually closer to the nucleus than the second type of endoplasmic reticulum, which you can see is the smooth ER. The rough ER, as its name implies, is going to have a rough ribosome-coated surface, which means that the rough ER is going to have a surface that is coated or studded with many ribosomes, making the surface of the rough ER appear to be rough. Recall from our previous lesson videos that ribosomes are non-membranous organelles that perform translation, the process of making proteins. Ribosomes make proteins, and because ribosomes are coating the surface of the rough ER, the rough ER will also be associated with these newly built proteins. Newly built proteins will fold and can be modified in the rough ER lumen or inside the rough ER.
The second main type of ER is going to be the smooth ER, commonly abbreviated as the SER. The smooth ER, or the SER, is going to be further from the nucleus compared to the rough ER, and, as its name implies, the smooth ER is going to have a smooth surface that is ribosome-free. The smooth ER does not have any ribosomes on its surface, and so its surface appears to be smooth in comparison to the rough ER, which has lots of ribosomes on its surface, making the surface rough. Because the smooth ER lacks ribosomes, it is ribosome-free and is not going to be associated with making proteins. Instead, the smooth ER is going to be associated with synthesizing lipids as well as detoxifying drugs and poisons.
If we take a look at our image down below, we can further distinguish between the rough ER and the smooth ER. Notice on the left-hand side over here we're showing our representation of a eukaryotic cell, and what you'll notice is that if we zoom into the cell here, that it is going to have, if we zoom into this region, that's what this image is showing you. You can see that we have the nucleus here in the center, and you'll notice that we have the rough ER here in a darker shade of red so we can go ahead and label it as the rough ER. Then in this lighter-colored structure over here, this is actually going to be the smooth ER. So we can label it as so. All of these little blue dots that you see throughout our image all over, all of these little blue dots, as you can see indicated by this blue arrow right here, these are going to be the ribosomes. Notice that the rough ER appears to have a rough surface because it is studded and coated with these ribosomes. Whereas the smooth ER, which is over here, notice that it is not coated with those ribosomes, and so its surface appears to be smooth.
This here concludes our brief introduction to the endoplasmic reticulum, the smooth ER, the rough ER, and the smooth ER, and we'll be able to get some practice applying these concepts and learn more as we move forward. So I'll see you all in our next video.