Endocytosis & Exocytosis - Video Tutorials & Practice Problems
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Endocytosis & Exocytosis
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Video transcript
Alright. So now that we've covered molecular transport of really small molecules, including passive transport and active transport, we're finally going to move on to the last section of our map of the lesson on membrane transport, Now macro Now macro prefix and macromolecules really just means large, and so macromolecules include really really large proteins, polysaccharides, and DNA molecules as well. And these macromolecules are simply just way too large in order to diffuse through membranes or channels, And so they will not be able to use the mechanisms of molecular transport that we talked about in our previous lesson videos, including the forms of passive transport or the forms of active transport that we discussed. And so instead these macromolecules must be transported across cell membranes using the process of either endocytosis and or exocytosis, as you can see down below in our map. And so we'll be able to define endocytosis and exocytosis a little bit later in our course. But for now, I'd like to foreshadow for you guys that integral membrane proteins, very specific ones called fusion proteins, are really important to the process of, endocytosis and exocytosis. And so these fusion proteins are integral membrane proteins that help fuse membranes as their name implies, and both, again, the process of endocytosis and exocytosis. But really moving forward in our course, we're really only going to talk about fusion proteins in the context of exocytosis, more specifically in the process of neurotransmitter release. But it's important to also keep in mind that fusion of membranes also takes place in endocytosis as well, and there are fusion proteins that we're not really going to talk about that are involved in the process of endocytosis, as well. And so of course because we're exploring our map using the leftmost branches first, in our next video we're going to explore endocytosis and the different types of endocytosis. So I'll see you guys in that video.
2
concept
Endocytosis & Exocytosis
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4m
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Video transcript
In this video, we're going to introduce endocytosis. And really the biggest takeaway of this video is that endocytosis allows entry into the cell. And so endocytosis is really just defined as macromolecule engulfment by the cell membrane allowing entry into the cell as a lipid vesicle. And so really the e n in endocytosis can remind you of the e n in engulfment and the e n in entry to the cell. And really there are 3 main types of endocytosis that you guys should be somewhat familiar with, and you can see that we're going to introduce those 3 down below. And of course the numbers that you see up above here correspond with the numbers that you see in our image down below. And so the first type of endocytosis that you guys should know is phagocytosis. And so phagocytosis is when large and solid materials are taken up by the process of endocytosis, also known as cellular eating. And again, it's called cellular eating because the materials that are brought in are large and solid, and so it's almost like the cell is eating something. Now the second type of endocytosis that you guys should know is pinocytosis. And so pinocytosis is when small and liquid materials are taken up by the process of endocytosis, also known as cellular drinking. And again it's called drinking because the materials that are brought into the cell are small and liquid. Now the 3rd and final type of endocytosis that you guys know is really just a specific type of pinocytosis, which is why we have this indentation here to show that it's really just a subtype of the previous. And so this third type is called receptor mediated endocytosis. And again, it's just a specific form of pinocytosis that uses receptor proteins. And so we'll be able to see examples of each of these down below in our image. And so on the far left over here what we have is an example of phagocytosis. And so notice over here what we have is the cell's plasma membrane and you can see the blue background represents the outside of the cell and this other background represents the inside of the cell. And so you can see that during the process of phagocytosis, really large and solid materials such as an entire bacterium and multiple bacteria even can be brought into the cell here as you can see by this arrow in the form of a lipid vesicle. And so phagocytosis is a process that is utilized by some of our white blood cells and so it can be involved in immunity, essentially protecting us from harmful bacteria. But also phagocytosis could be just a general process that's used to bring in nutrients to the cell. Again, another reason why it's referred to as cellular eating. Now over here in the middle, what we have is the process of pinocytosis, and really the biggest difference is the types of molecules that are brought in. Because notice here what we have are very small and liquid type of materials that are being brought into the cell. So again, it's a type of cellular drinking. Now the 3rd and final type of endocytosis is receptor mediated endocytosis, and notice that it's really just a specific type of pinocytosis. You can see that the materials are very very similar, but really the biggest difference is that there are receptor proteins. As you can see here, we're labeling these orange structures embedded in the membrane as receptors, and these receptor proteins are, involved in the endocytotic allows entry into the cell. And so we'll be able to get a little bit of practice with these concepts in our next video, and then we'll talk about exocytosis. So I'll see you guys there.
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Problem
Problem
Which of the following is FALSE about endocytotic movements?
A
Phagocytosis could be used against invading microorganisms.
B
Ingestion of plasma membrane along with extracellular fluid is a kind of pinocytosis.
C
Phagocytosis is a means of feeding in some eukaryotes and is important in animal nutrition.
D
The materials engulfed will be enclosed by a small portion of the ER membrane.
4
concept
Endocytosis & Exocytosis
Video duration:
2m
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Video transcript
So now that we've covered endocytosis, in this video we're going to introduce exocytosis. And really the biggest takeaway of this video is that exocytosis allows exiting from the cell. And so exocytosis is really defined as vesicle fusion with the cell membrane allowing the vesicle contents to exit the cell into the extracellular space. And so you can think that the EX in exocytosis is for the EX in exit and the EX of extracellular space. Now many biological processes rely on exocytosis, and so neurotransmitters and zymogens of digestive enzymes are just specific examples of substances that are released by exocytosis. And so if we take a look at our image down below, notice that this here represents a cell's plasma membrane. And so over here you can see the white background represents the outside of the cell or the extracellular space. And of course, this other background over here represents the inside of the cell. And so here what you can see is that there's a vesicle filled with some cellular contents, perhaps neurotransmitters or perhaps zymogens of digestive enzymes, and this vesicle filled with, contents are is making its way towards the cell's plasma membrane, and ultimately what it does is it begins to fuse with the cell's plasma membrane until it is fully fused with the cell's plasma membrane and the vesicle contents are released to the outside of the cell, to the extracellular space. And so you can see here that the vesicle contents here are exiting the cell, and again, that's the biggest takeaway of this video. And so this here concludes our introduction to exocytosis and we'll be able to get some practice applying these concepts in our next couple of videos. So I'll see you guys there.
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Problem
Problem
Which of the following is NOT a true statement regarding exocytosis?
A
It forms intracellular vesicles from inward folding of the plasma membrane.
B
It requires fusion of vesicles with the plasma membrane.
C
It secretes large molecules out of the cell.
D
It is responsible for neurotransmitter release of acetylcholine to stimulate muscle contractions.
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Problem
Problem
Label the following phrases based on if they apply to A) Only Endocytosis, B) Only Exocytosis, or C) Both:
a) Decreases the surface area of the plasma membrane: _________.
b) Increases the surface area of the plasma membrane: _________.
c) Secretes large molecules out of the cell: _________.
d) Brings molecules into the cell: _________.
e) Requires cellular energy: _________.
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7
Problem
Problem
Which means of particle transport is shown in the figure below?