In this video, we're going to talk about the 3rd organelle of the endomembrane system, which is the Golgi apparatus. Now molecules that are synthesized or built in the endoplasmic reticulum, such as proteins in the rough ER and lipids in the smooth ER, these molecules are transported by vesicles or tiny little membrane bubbles. These molecules that are transported by vesicles can be transported to the Golgi apparatus. The Golgi apparatus is really just a stack of flat membranous sacs. And because it is membranous, it's no surprise that it's part of the endomembrane system. The stacks of flat membrane sacs have a scientific name that is cisternae. Cisternae is just the scientific name that's referring to those flat membranous sacs. The Golgi apparatus's function is to act as a processing center because it's able to receive packages, modify the contents of the packages, and then deliver the packages. It's acting like a processing center in that way. The Golgi apparatus is capable of receiving vesicles that transport molecules that are being synthesized by the ER, either proteins or lipids. So, the Golgi apparatus receives those vesicles and then it modifies the vesicle contents, which would again either be proteins or lipids. After it modifies the vesicle contents, it will actually repackage the modified contents back into vesicles for export from the Golgi apparatus. This is why the Golgi apparatus functions as a processing center because it receives vesicles, it modifies the vesicle contents, and then it repackages the contents for export either out of the cell or to a different location within the cell. This means that the Golgi apparatus is going to have a receiving end where it receives vesicles, and that's going to be the receiving end of the Golgi apparatus referred to as the cis end of the Golgi apparatus. The shipping end, which is basically the end that repackages and exports, the shipping end of the Golgi apparatus is going to be the trans end of the Golgi apparatus. Some of the vesicles that are being shipped from the Golgi apparatus can actually fuse with the cell membrane for secretion. This is why the Golgi apparatus here is one of the last organelles involved in protein secretion.
The Golgi apparatus in this image is this pink structure that you see right here. You can see its position relative to other organelles that we already talked about in our previous lesson videos such as the nucleus, the rough endoplasmic reticulum, and the smooth endoplasmic reticulum. Here's a different view of the Golgi apparatus and some of these other organelles. Notice it's a bird's eye view. Here we have the nucleus. We're showing you only the smooth ER for simplicity's sake. We're showing you the rough ER, the one that's here in blue. The rough ER is studded with ribosomes. Those ribosomes make proteins, and those proteins can end up on the inside of vesicles, these little tiny membrane bubbles. This here is representing a vesicle that's carrying a protein because it's coming from the rough ER. The vesicles, the receiving end of the Golgi apparatus, recall the receiving end of the Golgi apparatus is going to be the cis end of the Golgi apparatus. Once those contents make it to the Golgi apparatus, they get modified and they make their way through the Golgi apparatus until they get to the other side of the Golgi apparatus, which is going to be the shipping end of the Golgi apparatus or the trans end of the Golgi apparatus. Down below, this end over here is going to be the trans end of the Golgi apparatus or the trans face of the Golgi apparatus. This means that vesicles are going to be created at this end and these vesicles are carrying the modified contents. These vesicles can travel to the cell membrane as we indicated above. They can travel and fuse with the cell membrane for secretion. At this point, traveling to the cell membrane, the contents can be exported and released to the outside of the cell. Once again, each of these flat sacs that you see here, these flat membranous sacs, is referred to as cisternae. The cisternae, once again, are the flat membranous sacs of the Golgi apparatus. This here concludes our introduction to the Golgi apparatus and the organelles involved with protein secretion. We'll be able to get some practice applying the concepts that we've learned in our next video here. I'll see you all there.