Hi. In this video, we're going to be talking about lysosomal and other degradation pathways. So, first, we're going to talk about the lysosome. Everything that the lysosome needs and has and does in order to degrade things. The lysosome actually contains many enzymes that degrade intracellular and extracellular materials. You can think of the lysosome as the cell's stomach. When things come in, whether it's from the internal environment or the external environment, they are going to get degraded. How it actually degrades is very similar to the stomach. The lysosome is actually very acidic, and it maintains that acidity because there's an ATP pump that's responsible for pumping protons across the membrane. Here, we have another proton gradient. In Cell Biology, we deal a lot with proton gradients, and this gradient is really important because it maintains that acidity, the cell's stomach, so that it can degrade things. But you may ask, well, that's great, but why doesn't the lysosome degrade itself if it's so acidic? The reason it doesn't degrade itself is because those membrane lipids and proteins have a lot of glycosylation. What that means, first, do you remember what glycosylation is? Right. It's going to be the addition of sugars, and it can happen on lipids or proteins. But either way, it stops that acidity from affecting the lysosomal membrane and the lysosomal proteins themselves. So, they can exist in this acidic environment. It's very similar to the way your gut cells function. Your stomach doesn't digest itself. So the lysosome doesn't digest itself. It's just the place for digestion. The enzymes responsible for this digestion or degradation are called lysosomal acid hydrolases. They break down all different kinds of materials and there are a lot of them, around 50 types in every single lysosome. Here we have a lysosome. I don't know why these have faces on them, but they do. But, anyway, these are the proteins and enzymes, all the different kinds that can degrade proteins, inside the lysosome. I don't know. Maybe the happy ones are just happy about degrading things. What proteins actually get degraded in the lysosome? Well, proteins that need to get to the lysosome must contain the appropriate mannose 6-phosphate tag. And so lysosomal proteins that need to get to the lysosomes, these are these acid hydrolases, different types of membrane proteins, any specifically lysosomal protein has to have this mannose 6-phosphate tag. Once it has that signal on it, the lysosomal receptors will actually recognize it. These are actually found in the Golgi. That's important. So it's a little misleading. Lysosomal receptors, you think that's in the lysosome. Eventually, they make it there, but, to begin with, those proteins start out in the ER and the Golgi. They need to be sorted to the lysosome. So they bind these receptors in the Golgi, and then, once that tag is interacted with this lysosomal receptor, they're going to be sorted into transport vesicles and travel to the lysosome where they can then exert their function. Here we have a protein here and it needs to get to the lysosome. That's where its function is. So, it binds to lysosomal receptors in the Golgi. Once it's bound, that vesicle will bud off and it will travel to the lysosome where this protein gets released, and then it can exert its function. This is a pretty important pathway to know. You have your cargo, it binds to the lysosomal receptors in the Golgi, once it's there, travels to the lysosome, and it enacts its function. Super, super important. So with that, let's now turn the page.
Lysosomal and Degradation Pathways: Study with Video Lessons, Practice Problems & Examples
Created using AIThe lysosome functions as the cell's digestive system, containing enzymes called lysosomal acid hydrolases that degrade various materials. It maintains an acidic environment through an ATP-driven proton pump, preventing self-digestion due to glycosylation of its membrane proteins. Proteins destined for the lysosome require a mannose-6-phosphate tag for recognition by lysosomal receptors in the Golgi apparatus. Additionally, autophagy and phagocytosis are key degradation pathways, where autophagosomes and phagosomes fuse with lysosomes to form autolysosomes and phagolysosomes, respectively, facilitating the breakdown of cellular components and external particles.
Lysosomal Sorting
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Autophagy
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Okay. So, in this video, I'm going to be talking about other degradation pathways in the cell. The first one is going to be autophagy. Autophagy involves the process of the cell eating itself. This occurs when the cell controls its own death or the degradation of certain large entities within the cell. It does this by degrading large molecules or organelles in the cell. This happens as autophagosomes form, which are membrane-enclosed compartments that can enclose old organelles, such as old Golgi components or old mitochondria that are dying and need to be degraded. Autophagosomes will enclose them with a double membrane. Remember, this is a double membrane. Then you have this huge compartment, right, with this old dead mitochondria or chloroplast or whatever it is in it. This huge complex will actually end up fusing with a lysosome, and this is called an autolysosome because it has to get pretty large, much larger than a lysosome would normally be. It has a special name. You may actually see this sometimes called macrophagy because it's large. Microphagy is a different process with a smaller vesicle and also a single bilayer, but autophagy is going to be macrophagy because it's huge. Remember, the autophagosome has this double membrane. You have a lysosome, so this is going to have something in it. We'll just say this is the mitochondria. It's dead. It's dying. It doesn't want to be there. It needs to be degraded. This actually fuses with the lysosome to create this autolysosome, this huge complex macrophage. Eventually, the autophagosome and the mitochondria will get degraded.
A separate degradation pathway is called phagocytosis, and I know you heard about this in your intro class. This is going to be the process of the cell actually internalizing large particles from the extracellular environment. When it internalizes these large extracellular molecules, it forms phagosomes, which also enclose these molecules with a double membrane. This double membrane is a very repetitive theme throughout these other degradation pathways that is important. Eventually, like the autophagosome, this phagosome will fuse with the lysosome to form the phagolysosome. This is also called macrophage because it's dealing with large particles. So, here we have a bacteria, for example, as a large particle. It undergoes phagocytosis, enters into a phagosome. It eventually fuses with a lysosome to form a phagolysosome, and this is degraded. Sometimes that can be just released, or it can be further degraded and used by the cell, whatever it wants to do. But it forms these cytolexosomes in order to be degraded.
So those are the overview of the two other degradation pathways that we're going to talk about. So with that, let's turn the page.
Which of the following terms describes the cell eating itself?
The mannose 6 phosphate tag is added onto proteins for what region?
Macrophagy differs from microphagy in which of the following ways?
Here’s what students ask on this topic:
What is the function of lysosomes in the cell?
Lysosomes function as the cell's digestive system. They contain enzymes called lysosomal acid hydrolases that degrade various intracellular and extracellular materials. The lysosome maintains an acidic environment through an ATP-driven proton pump, which is crucial for the activity of these enzymes. This acidic environment is similar to the stomach's, allowing the lysosome to break down proteins, lipids, and other macromolecules. The lysosome's membrane is protected from self-digestion by glycosylation, which involves the addition of sugars to its membrane proteins and lipids.
Created using AIHow do proteins get targeted to the lysosome?
Proteins destined for the lysosome require a mannose-6-phosphate (M6P) tag. This tag is recognized by lysosomal receptors located in the Golgi apparatus. Once the M6P-tagged protein binds to these receptors, it is sorted into transport vesicles that bud off from the Golgi and travel to the lysosome. Upon reaching the lysosome, the protein is released and can exert its function. This targeting mechanism ensures that lysosomal enzymes and other proteins reach their correct destination within the cell.
Created using AIWhat is autophagy and how does it work?
Autophagy is a cellular degradation pathway where the cell degrades its own components, such as damaged organelles or large molecules. During autophagy, double-membrane structures called autophagosomes form around the material to be degraded. These autophagosomes then fuse with lysosomes to create autolysosomes, where the enclosed material is broken down by lysosomal enzymes. This process helps the cell maintain homeostasis and recycle cellular components.
Created using AIWhat is the difference between autophagy and phagocytosis?
Autophagy and phagocytosis are both degradation pathways but differ in their targets and mechanisms. Autophagy involves the degradation of the cell's own components, such as damaged organelles, through the formation of autophagosomes that fuse with lysosomes. Phagocytosis, on the other hand, involves the internalization of large extracellular particles, such as bacteria, into phagosomes. These phagosomes also fuse with lysosomes to form phagolysosomes, where the ingested material is degraded. Both processes involve the fusion with lysosomes but target different types of material.
Created using AIWhy don't lysosomes digest themselves?
Lysosomes do not digest themselves due to the glycosylation of their membrane proteins and lipids. Glycosylation involves the addition of sugar molecules, which protect the lysosomal membrane from the acidic environment inside the lysosome. This protective mechanism is similar to how the stomach lining prevents self-digestion. Additionally, the enzymes within lysosomes are specifically activated by the acidic pH, ensuring they function optimally only within the lysosome and not elsewhere in the cell.
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