Endocytosis and Exocytosis - Online Tutor, Practice Problems & Exam Prep

Endocytosis and Exocytosis

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, they're simply just way too large to diffuse through membranes or even to move through protein channels.

They're not able to diffuse through the methods that we've talked about so far. Instead, large macromolecules will be transported across cell membranes via either the process of endocytosis or the process of exocytosis. We'll talk a lot more about endocytosis and exocytosis as we move forward in our course. Below here, we're showing you a snippet of our map of the lesson on membrane transport. Notice that we're focusing on bulk transport or the transport of very large molecules.

These large molecules can either be transported via endocytosis to enter the cell or exocytosis to exit the cell. We're going to start off our lesson by focusing on endocytosis, entering the cell. There are three types of endocytosis that we're briefly going to touch on, which are phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis, a form of pinocytosis. Later, after we talk about endocytosis, we'll discuss 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 Allows Entry to the Cell

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 3 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 it is, 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 being brought in as pinocytosis. But the real difference is that receptor-mediated endocytosis uses these orange receptors that you can see 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 vessel.

And so the big idea here is that receptor-mediated endocytosis uses these receptors, these orange receptors. And so 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

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 ________.

• A. Pinocytosis brings only water molecules into the cell, receptor-mediated endocytosis brings in other molecules also
• B. Pinocytosis increases the surface area of the plasma membrane, receptor-mediated endocytosis decreases it
• C. Pinocytosis is nonselective, receptor-mediated endocytosis offers more selectivity
• D. Pinocytosis can concentrate substances from the extracellular fluid, receptor-mediated endocytosis cannot

Exocytosis Allows Exiting from the Cell

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. And so the EX in exocytosis is going to be very helpful for you all to remember exactly what exocytosis is about. And so 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. And so 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 the examples of molecules that can undergo exocytosis, allowing exiting from the cell. So let's take a look at our image down below to get a better understanding of this. And 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. And so 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. And 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.

And so ultimately, what we get is the vesicle contents are being released into the outside of the cell, and so these contents are exiting the cell, via exocytosis. And so 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. So I'll see you all in our next video.

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 removing large waste particles that cannot be recycled by the cell.

Which means of particle transport is shown in the figure below?

• A. Exocytosis
• B. Endocytosis
• C. Facilitated diffusion
• D. Simple diffusion

Here’s what students ask on this topic:

What is the difference between endocytosis and exocytosis?

Endocytosis and exocytosis are processes used by cells to transport large molecules across the cell membrane. Endocytosis involves the engulfment of substances into the cell, forming vesicles from the plasma membrane. It includes three types: phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis. Exocytosis, on the other hand, involves the fusion of vesicles with the plasma membrane to release their contents outside the cell. This process is crucial for the secretion of hormones, neurotransmitters, and digestive enzymes. Both processes are essential for maintaining cellular functions and homeostasis.

What are the three types of endocytosis?

The three types of endocytosis are phagocytosis, pinocytosis, and receptor-mediated endocytosis. Phagocytosis, or cell eating, involves the engulfment of large solid particles, such as bacteria, into the cell. Pinocytosis, or cell drinking, involves the uptake of small liquid particles. Receptor-mediated endocytosis is a specialized form of pinocytosis that uses receptor proteins to specifically bind and internalize certain molecules. These processes allow cells to intake various substances necessary for their functions.

How does receptor-mediated endocytosis differ from pinocytosis?

Receptor-mediated endocytosis is a specific form of pinocytosis that involves the use of receptor proteins on the cell membrane. These receptors specifically bind to target molecules, allowing for the selective uptake of substances into the cell. In contrast, pinocytosis is a non-specific process where the cell engulfs extracellular fluid and its dissolved solutes without the use of specific receptors. Receptor-mediated endocytosis ensures that only certain molecules are internalized, making it a more selective and efficient process compared to general pinocytosis.

What role does exocytosis play in cellular function?

Exocytosis plays a crucial role in cellular function by allowing the cell to expel various substances into the extracellular space. This process involves the fusion of vesicles with the plasma membrane, releasing their contents outside the cell. Exocytosis is essential for the secretion of hormones, neurotransmitters, and digestive enzymes. It also helps in removing waste products and maintaining the cell's internal environment. By facilitating the export of important molecules, exocytosis supports various physiological processes and overall cellular homeostasis.

What types of molecules are typically transported via exocytosis?

Exocytosis typically transports a variety of molecules, including hormones, neurotransmitters, and digestive enzymes. Hormones are released into the bloodstream to regulate various physiological processes. Neurotransmitters are secreted by nerve cells to transmit signals across synapses. Digestive enzymes are released into the digestive tract to aid in the breakdown of food. These molecules are packaged into vesicles within the cell, which then fuse with the plasma membrane to release their contents into the extracellular space. Exocytosis is essential for the proper functioning of these and other cellular activities.