In this video, we'll discuss the standard level or core curriculum from B2.2 on organelles and compartmentalization. Now, an organelle can be defined as a structure that is specialized for a specific function within a cell. Okay, so it's got to be something within a cell, and it has to have a specific function. These are covered in much greater detail in A2.2, which is all about cell structure. But for now, we'll just go over basic features, right?
So any cell structure that has a specific function within a cell, like the mitochondria or the rough ER, things like that, those are organelles. There are some cell structures that are important, but just are not considered an organelle. So things like the cell wall or the cytoskeleton or even that cytoplasm, they're all important, but they are not an organelle. A lot of students get confused into thinking that organelles is what separates prokaryotes from eukaryotes, and that's not quite right.
Prokaryotes do have some organelles, but they don't have any organelles that are surrounded by a membrane or membrane-bound organelles. So let's take a look at the different types of organelles and which ones have membranes. So things like ribosomes or centrioles or microtubules.
Those do not have a membrane surrounding them. There are some structures that are membrane bound by only one membrane, and that includes things like the Golgi apparatus, lysosomes, vacuoles and vesicles, and both the smooth and the rough endoplasmic reticulum. Things like the nucleus, the mitochondria, and chloroplast, those all have not one, but two membranes.
They are double membrane bound. And so it's important to understand which features or which structures in the cell, which organelles are going to have different numbers of membranes. So again, non-membrane bound organelles, okay, we can find those in prokaryotes, but you won't find any of these. Anything surrounding a membrane-bound or anything that has a membrane-bound organelle must only be found in eukaryotic cells. Now, speaking of eukaryotes, we often refer to them as being compartmentalized.
Well, compartmentalized just means that they have these membrane-bound organelles. And it seems quite complicated. So what's the advantage of having those?
Well, when it comes to something like the nucleus, that's really great in terms of protecting the DNA. Now you may remember in prokaryotes, it's just free floating and also for mRNA editing. So what's going to happen is when we have a cell and we're going to do transcription, DNA is going to be transcribed into mRNA inside the nucleus.
We have the option of editing that mRNA before it goes out and is translated by one of the ribosomes. Prokaryotes, because they don't have a nuclear membrane or don't have a nucleus, don't have the option of that mRNA editing. Prokaryotes also don't have the option of really surrounding and concentrating enzymes where they need to be. It's one of the reasons why prokaryotes must remain very small because it makes it easier for the virus to enter the body.
they need those enzymes to be in a certain place, but they don't have really a way of compartmentalizing them. So things like the mitochondria, let's say, surrounded by a double membrane, well, all of those enzymes that are necessary for doing whatever the mitochondria does can really be tightly concentrated in this small area due to that membrane, due to that compartmentalization. It can also maintain different areas that have different pHs or different solute concentrations, and that can be really necessary for specific cell functions.
So let's say I need something in a particular concentration over here, but not necessarily over here. Well, the membrane-bound organelles, that compartmentalization allows for that. And then of course, storing of dangerous substances. So something like a lysosome is going to be a membrane-bound structure, a membrane-bound organelle that can help you. contain these really destructive enzymes.
They're great for some things, but I don't want them running loose inside of the cell. So there are a lot of advantages here for compartmentalization. And one of the things I want you to make sure that you're associating with this is that this is a property of eukaryotic cells when we're talking about membrane-bound organelles. Prokaryotes are compartmentalized.
just in the fact that their cell membrane separates them from the outside environment. But in terms of form and function, if we're talking about compartmentalization in terms of these membrane-bound organelles, that is something that we want to associate with eukaryotic cells only.