In this video, we're going to begin our lesson on endocytosis and exocytosis. Up until this point in our course, we've been discussing the membrane transport of very small molecules. But what about large molecules? How do they get across a cell's plasma membrane? Well, large biomolecules, for example, large proteins, large carbohydrates, or nucleic acids like DNA, are simply too large to diffuse through membranes or even through protein channels. Therefore, they are not able to use the methods we have discussed so far. Instead, large macromolecules are transported across cell membranes via either the process of endocytosis and or the process of exocytosis. We'll discuss endocytosis and exocytosis more as we move forward in our course. Below here, we're showing you a snippet of our map of the lesson on membrane transport, focusing on bulk transport or the transport of very large molecules. These large molecules can either be transported via endocytosis to enter the cell and or exocytosis to exit the cell. We're going to start our lesson by focusing on endocytosis, entering the cell. There are three types of endocytosis that we're briefly going to touch on: phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis, which is a form of pinocytosis. Later, after we discuss endocytosis, we'll talk about exocytosis, exiting the cell. But for now, this concludes our introduction to endocytosis and exocytosis, and we'll learn more about these processes as we move forward in our course. So, I'll see you all in our next video.
Endocytosis and Exocytosis - Video Tutorials & Practice Problems
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Endocytosis and Exocytosis
Video transcript
Endocytosis Allows Entry to the Cell
Video transcript
In this video, we're going to focus on endocytosis and how endocytosis allows entry into the cell. And so the EN in endocytosis is going to be very helpful to remind you about what it does, and that's because endocytosis is defined as macromolecule engulfment by the cell membrane allowing for entry into the cell via a lipid vesicle. And so you can see the EN in endocytosis is for the EN in engulfment and the EN in entry. And so the big idea here is that molecules are going to be brought into the cell with endocytosis.
Now really there are three main types of endocytosis that you all should know. The first type is phagocytosis. Now phagocytosis is when a large solid material is being taken into the cell via endocytosis. And because it is a solid material, it's commonly known as cell eating.
Now, the second type of endocytosis that you all should know is pinocytosis. And pinocytosis is defined as when a small liquid material is being taken into the cell by endocytosis. And because the materials are liquid, it's commonly known as cell drinking.
And then the third and final type of endocytosis that you all should know is receptor-mediated endocytosis. And really, receptor-mediated endocytosis is just a special form of pinocytosis, and that's why we have this little indentation here to show that, hey, receptor-mediated endocytosis is just a special type of pinocytosis. And it says here it's a specific form of pinocytosis that uses receptor proteins.
So let's take a look at our image down below to get a better understanding of these ideas. So on the far left over here, notice that we're showing you the first type of endocytosis, phagocytosis. And so notice that the outside of the cell is over here and the inside of the cell is over here, and notice that a bacterium is being brought into the cell here, and when it's brought into the cell, it ends up inside of a lipid vesicle. And recall, vesicles are just these little membrane bubbles, and it will bring in these large solid materials such as the bacteria here.
Now moving on, pinocytosis is over here in the middle and notice that the outside is over here and the inside of the cell is over here, and so these small liquid materials are being brought into the cell via a lipid vesicle. And so this is pinocytosis or cellular drinking.
Now the final type of endocytosis that you all should know is receptor-mediated endocytosis, which is really just a form of pinocytosis, so cellular drinking. So you can see the same blue molecules embedded in the membrane at these positions here. And so, the receptors are proteins that have a specific binding attraction to these blue liquid molecules. And then, of course, because it's a form of endocytosis, it's going to be brought into the cell in a lipid vesicle. And so the big idea here is that receptor-mediated endocytosis uses these receptors, these orange receptors.
This here concludes our introduction to endocytosis and how endocytosis, the EN, is going to remind you that it allows for entry into the cell. And so we'll be able to talk about exocytosis in our next video. So I'll see you all there.
Endocytosis and Exocytosis Example 1
Video transcript
Alright. So here we have an example problem that says white blood cells of our immune systems engulf bacteria using which type of endocytosis? And we've got these 4 potential answer options down below. Now, after reading through these options, we know from our last lesson video that phagocytosis and pinocytosis are definitely types of endocytosis that we talked about in our last lesson video. But osmosis is definitely not one of the types of endocytosis. And, also, when we look at option d, it says receptor mediated exocytosis. But receptor mediated exocytosis is not a type of endocytosis, and so receptor mediated endocytosis would be a type of endocytosis, but receptor-mediated exocytosis is not. And so, we did not talk about that in our last lesson video. So we can eliminate options c and d. So now we're between either option a or option b. And so, notice it's saying white blood cells of our immune systems engulf bacteria. And bacteria is going to be a solid. And because bacteria is a solid, it's going to be involved with cellular eating. And if it were a liquid, then it would be involved with cellular drinking. And recall from our last lesson video that it's phagocytosis that is involved with cellular eating, eating essentially solid materials like bacteria. And so pinocytosis is involved with cellular drinking, but again, bacteria are not liquids, they are solids. And so option b is not going to be correct, and option a is the correct answer to this example problem. So that concludes this example, and I'll see you all in our next video.
The difference between pinocytosis and receptor-mediated endocytosis is that ________.
Exocytosis Allows Exiting from the Cell
Video transcript
So, in our last lesson video, we talked about endocytosis and how it allows for entry into the cell. And so in this video, we're going to talk about the complete opposite of endocytosis, which is exocytosis, and how exocytosis allows exiting from the cell. The "EX" in exocytosis is going to be very helpful for you all to remember exactly what exocytosis is about. Exocytosis can be defined as vesicle fusion with the cell membrane, allowing the contents of the vesicle to exit the cell into the extracellular space or the outside space outside of a cell. You can think the “EX” in exocytosis is for the “EX” in exit and the “ex” in extracellular space. Now, there are many different types of molecules that can undergo exocytosis, but a few examples include hormones, neurotransmitters, and digestive enzymes. This is just a small subset of all of the examples of molecules that can undergo exocytosis, allowing exiting from the cell. Let's take a look at our image down below to get a better understanding of this. Notice the inside of the cell is over here on the right-hand side, and the outside of the cell is over here on the left-hand side. Notice that, originally, these red molecules that you see here that are representing hormones are inside of a vesicle, inside of a membrane bubble here on the inside of a cell. This membrane bubble, this vesicle can start to fuse with the cell's plasma membrane here. And when that vesicle fully fuses, it can release the contents that used to be on the inside of the vesicle. Ultimately, what we get is the vesicle contents being released into the outside of the cell. These contents are exiting the cell, via exocytosis. This here concludes our introduction to exocytosis and how it allows exiting from the cell, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.
Which of the following is NOT a true statement regarding exocytosis?
Which means of particle transport is shown in the figure below?