Endomembrane System: Protein Secretion - Video Tutorials & Practice Problems
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1
concept
Endomembrane System: Protein Secretion
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4m
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In this video, we're going to begin our introduction to the endomembrane system and to one of the major functions of the endomembrane system, which is protein secretion. And so the endomembrane system can be defined as a group of membrane bound organelles that are inside of a eukaryotic cell. And so the root endo- and endomembrane system means inside. And so you can see that we're talking about membranes that are found on the inside of the cell. And the system here is really just, referring to the fact that it's made up of a group of organelles, and all of these organelles are membrane bound, meaning that their boundaries are made up of membranes. Now the endomembrane system includes many different organelles that we're going to mention down below in this table. However, all of these organelles that are part of the endomembrane system are interconnected to each other by these structures that are called vesicles. And so vesicles is just a fancy name for these tiny little membrane bubbles that can carry materials on the inside. And so all of these organelles that are part of the endomembrane system, they are interconnected, by these vesicles, and we'll get to see examples of vesicles as we move forward in our course. Now the endomendobraining system has a lot of different functions. It has multiple functions, we're not gonna talk about all of the different functions. We're mainly going to focus on 2 of its functions. And, those include protein secretion, as well as cellular digestion. And so notice that down below in our example here, we have a table that shows the organelles of the endomembrane system. And notice that behind them, we have this green color coding that links, the organelles that we're gonna talk about in our course moving forward that are involved with protein secretion. And then, notice that in yellow, we have the organelles that are involved, with cellular digestion that we're gonna talk about moving forward in our course. And then, over here with this white background, we have the cell membrane, which we're not gonna focus on in this, particular portion of our lesson. We'll talk more about cell membranes, later in a different, lesson. However, what you'll see is that all of these numbers that you see here are showing you organelles that are part of the endomembrane system, and we have them grouped based on their functions, whether they're involved with protein secretion or cellular digestion. So moving forward in our course, we're gonna focus mainly on the organelles that are involved with protein secretion, which include the nuclear envelope or the nucleus of the eukaryotic cell, the endoplasmic reticulum of the eukaryotic cell, the Golgi apparatus, as well as transport vesicles, which we mentioned again are these little membrane bubbles. And then later in our course, we'll get to talk more about the, organelles of the endomembrane system that are involved in cellular digestion, which include, the lysosomes and peroxisomes, as well as, vacuoles, such as central vacuoles and things like that. And so this here really just, is outlining, the organelles of the endomembrane system and grouping them by their functions, and we'll get to talk more about each of these organelles that are on here as we move forward in our course. So that being said, I'll see you all in our next video.
2
concept
Protein Secretion
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1m
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So from our last lesson video, we know that one of the major functions of the endomembrane system is protein secretion. But what exactly does protein secretion even mean? Well, the word secretion is just a fancy name for a process by which a substance is released into the environment or released into the surroundings of the cell. And so protein secretion is a process by which a protein is being released into the environment or released into the surroundings of the cell. And so protein secretion involves several different organelles that interact with each other in a very specific order. And so moving forward in our course, we're going to talk about each of the organelles that are involved with protein secretion. And so here, we're showing you an image of these organelles, but moving forward in our course, we're going to talk about each of the organelles in their own endoplasmic reticulum and the Golgi apparatus that we see here. And so once again, we'll get to talk about each of these organelles moving forward in our course in their own separate video. So I'll see you all in our next video.
3
concept
Nucleus
Video duration:
6m
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In this video, we're going to talk about the first organelle of the endomembrane system, which is the nucleus. And so protein secretion is going to start in the nucleus, and this is because the nucleus of a eukaryotic cell stores the DNA of the cell. And recall that the DNA of the cell carries the recipe or the code for making the protein. And so that's exactly why protein secretion starts in the nucleus, because you can't secrete the protein until after you've made the protein. Now the nucleus can be defined as a rounded structure that contains and protects most of a eukaryotic cell's DNA. Now there are these three structures that we're gonna talk about, in the nucleus that you all should be aware of. Now remember that the nucleus is part of the endomembrane system, which means that its border is going to be a membrane itself. And the border of the nucleus has a specific name that we refer to as the nuclear envelope. And so the nuclear envelope is really just defining the double membrane barrier that surrounds the nucleus, and again acts as the barrier of the nucleus, basically separating the inside of the nucleus from the outside of the nucleus. Now nuclear pores are referring to tiny little pores or holes that are found in the nuclear envelope. And these tiny little nuclear pores or holes in the nuclear envelope are going to allow the entry and exit into and out of the nucleus. So they basically can control and monitor what leaves the nucleus and also what enters the nucleus. Now this other, word here, the nucleolus, is referring to a small dense structure that's on the inside of the nucleus, and this is specifically where ribosomes are assembled. And recall from our previous lesson videos that ribosomes are important for making proteins, which is another reason why the nucleus is the first step of protein secretion, because it is involved with making ribosomes. And so let's take a look at our image down below right here to get a better understanding of the eukaryotic nucleus. So over here on the left hand side, we're showing you our representation of the eukaryotic cell, and notice right here, we are showing you the nucleus of the cell. And so if we zoom in here to the nucleus of the cell, what you'll notice is that it is made up of a membrane, a double membrane. And this double membrane that you see here acts as the barrier of the nucleus. And so, the gray, structures that you see here are referring to the nuclear envelope. And And so we can label this as the nuclear envelope, the double membrane that surrounds the nucleus and acts as its barrier, basically what you see surrounding the nucleus here. Now notice that in the nuclear envelope, there are these holes that you see throughout, these pores, if you will, the nuclear pores. So, this hole that you see right here in the nuclear envelope is referring to the nuclear pore. Now notice that on the inside of the nucleus, we have DNA. And so these structures that you see here represent DNA, and the DNA, most of the eukaryotic cell's DNA is found inside of the nucleus, so that's important to keep in mind. Now, also, within the nucleus right here at the core of the nucleus, there's another small dense structure on the inside of the nucleus, and this is where ribosomes are going to be assembled. So this is specifically the nuclei oles. So this is the nucleolus, a structure within the inside of the nucleus itself that is involved with building or assembling ribosomes. Now, the reason once again that, the protein secretion process starts in the nucleus is because the nucleus is what is going to contain the DNA of the cell. And so the DNA of a cell, which is again found in the nucleus of the cell, is going to be transcribed into RNA, and then the RNA will then be translated into a protein itself. And, the protein, recall, is being built by the ribosome. And there's gonna be a lot more details on this process that we're mentioning right here, later in our course. And we'll talk more about this idea of transcription or being transcribed as well as translation, again, later in our course. For now, what you should note is that, protein secretion starts in the nucleus because, in order for a protein to be made, it first needs the DNA in the nucleus needs to be transcribed into RNA, and then the RNA needs to be translated into the protein. And then once the protein is made, it can then be, secreted. And so this here concludes our introduction to the nucleus, and we'll be able to talk more about the other organelles of the endomembrane system moving forward in our course. So I'll see you guys in our next video.
4
Problem
Problem
Which part of the nucleus is responsible for assembling ribosomes and ribosomal RNA?
A
The mitochondria.
B
Nuclear Envelope.
C
Nuclear pores.
D
Nucleolus.
5
concept
Endoplasmic Reticulum
Video duration:
8m
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In this video we're going to talk about the 2nd organelle of the endomembrane system which is the endoplasmic reticulum And so the endoplasmic reticulum is commonly abbreviated with the letters e r, and you'll see this abbreviation e r throughout our lesson moving forward a lot. And so 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. And so really, 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. Now, 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. And so 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 number 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. Now 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. And 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. And so, recall from our previous lesson videos that ribosomes are non membranous organelles that perform translation. The process of making proteins. And so ribosomes make proteins and because ribosomes are coating the surface of the rough ER and again ribosomes make proteins, the rough ER will also be associated with these newly built proteins. And so, the newly built proteins will actually fold and can be modified in the rough ER lumen or in the inside of the rough ER, newly built proteins are able to fold and be modified. Now the second main type of ER is going to be again the Smooth ER and the Smooth ER is commonly abbreviated as the SER. And so, the smooth ER or the SER is going to be further from the nucleus in comparison to the rough ER and as its name implies, the smooth ER is going to have a smooth surface that is going to be ribosome free. And so, 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. Now again because the Smooth ER lacks ribosomes, it's ribosome free, it is not going to be associated with making proteins. Instead, the smooth er is going to be associated with synthesizing or making lipids as well as detoxifying drugs and poisons. And so if we take a look at our image down below, we can further distinguish between the rough ER and the smooth ER. And so notice on the left hand side over here we're showing you 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 And then in this lighter colored structure over here, this is actually going to be the smooth ER. So we can label it as so. And 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. And so 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. And so, 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.
6
concept
Golgi Apparatus
Video duration:
6m
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In this video we're going to introduce the 3rd organelle of the endomembrane system which is the Golgi apparatus. And so what's important to note is that molecules that are synthesized or built in the endoplasmic reticulum or the ER such as proteins that are built in the rough ER and lipids that are built in the smooth ER are going to be transported by vesicles or these little membrane bubbles to the Golgi apparatus. And so the Golgi apparatus is really just a stack of flat membranous sacs and because it is membranous it's no surprise that the Golgi apparatus is part of the endomembrane system. Now these flat membranous sacs are specifically referred to as cisternae And so this term here cisternae just refers to the flat membranous sacs that make up the Golgi apparatus. Now the Golgi apparatus functions as a processing center and this is because the Golgi apparatus is going to receive packages, modify the contents of those packages and then repackage those modified contents and distribute those modified contents to different parts of the cell or outside of the cell. And so once again the Golgi apparatus is going to receive vesicles, and then it will modify the vesicle contents, then it will repackage the contents into vesicles for export of those contents out of the Golgi apparatus. And so those contents can again either be distributed to different locations within the cell or perhaps, to a location outside of the cell so that those contents are secreted. And so, in this case, what this means is that the Golgi apparatus must have a receiving end and so the receiving end of the Golgi where it will be receiving packages is going to be called the sys end And then the shipping end of the Golgi where it will be repackaging and distributing these contents is going to be called the trans end of the Golgi apparatus. Now some vegetables are going to be shipped from the Golgi apparatus and confused with the cell membrane allowing for those contents to be secreted. And so, this will allow for secretion and again secretions just a fancy term that means being released into the environment of the cell. And so, this is why the Golgi apparatus is one of the final organelles in protein secretion. And so if we take a look at our image down below, we can get a better understanding here of this Golgi apparatus. And so notice on the left hand side we're showing you an image that should look familiar to you from some of our previous lesson videos where you can see, the nucleus of the cell here which is surrounded by the endoplasmic reticulum, the rough ER and the smooth ER over here. And then notice in this image we're introducing the Golgi apparatus and so you can see the Golgi apparatus is right here within this image. Now on the right hand side we're showing you a bird's eye view, a different vantage point of these same sets of organelles over here. And what you'll notice is that it's showing you the nucleus of the cell and then it's only showing you the rough endoplasmic reticulum or the rough ER just for simplicity and the smooth ER is not being shown on the right hand side. Again, just for simplicity here. And so what you'll notice is that this rough ER is gonna be studded with ribosomes and so those ribosomes will make proteins, those proteins will end up in the lumen of the rough ER and then those proteins can end up in these little membrane bubbles that are called vesicles. So these are vesicles that are going to be carrying proteins because these vesicles are budding from the rough ER. And so these vesicles again can make their way to the Golgi apparatus and so the Golgi apparatus is going to have a receiving end and the receiving end where it receives packages is going to be called the cis end or the sys face of the Golgi and then, those packages that are received will be modified throughout the Golgi apparatus until it gets to the trans end. And so here we can say this is the trans end of the Golgi or the trans face of the Golgi. And this is going to be the shipping end where the modified contents are going to be repackaged into vesicles and those vesicles can either be distributed to different locations within the cell or those vesicles could travel to the cell membrane where they can fuse with the cell membrane and release the contents of those, vesicles. And so, each of these little individual membranous, flat membranous sacs that you see here is, the cisterna. And so we can go ahead and label those right here. And so really this is the pathway for protein secretion. Proteins will be made in these ribosomes in the rough ER, they'll go to vesicles then they'll go to the cis face of the Golgi, be modified in the Golgi, go to the trans face of the Golgi, be repackaged into vesicles and then they'll make their way to the cell membrane where those proteins will be secreted. And so this here concludes our brief introduction to the Golgi apparatus and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.