Hello, AP Biology students. Let's go over the fifth section in Unit 3. In this section, we're going to go over my favorite topic in Unit 3, and it's called compartmentalization. We can tie this word of compartmentalization into our last unit when we talk about cells. Let's first talk about something called a metabolic pathway.
This is basically a series of linked reactions. As you can see in our diagram here, A is going to be changed into B by enzyme 1. B is then going to be changed into C by enzyme 2, and so on and so forth. But basically what we're seeing here is the product of one reaction is going to become the substrate of the next reaction.
This is a pathway where several enzymes are going to work together to change one molecule into a different molecule with a lot of intermediate steps. Sometimes these metabolic pathways become cycles. As you can see, we have this chain or pathway here, but sometimes they go in a cycle or in almost like a circular pattern. Before I go any further, please understand that in your cells, in your organelles, that the molecules aren't actually going around in a circle. We show them in a circle to help us better understand and teach this process, but don't think in your cells these molecules are standing still and they're just kind of going in a circle.
No, we're just showing that in a circle to help us understand it. All right, so what is compartmentalization? Compartmentalization is the division of something larger into smaller sections for specific functions. I always like to talk about a house being compartmentalized. It's a larger structure with smaller units like you have like the basement, the kitchen, maybe like a bedroom, work area, office.
Each of these different smaller areas is sectioned off and is focused on one particular function. If this whole building was just one big room, it wouldn't be as efficient as having smaller rooms for specific functions. For example, the kitchen. We need all of the kitchen appliances in one small area to help with efficiency. If this was like one big house and you had parts of the kitchen all over the place, it wouldn't be efficient because you'd be traveling back and forth throughout the whole house just to cook a meal.
We focus all of those items that we need in a kitchen in one small area to make it more efficient. My students are probably rolling their eyes because I love that word efficiency. It's basically talking about the return on investment when looking at energy. What we do in a cell is we compartmentalize the different parts in the cell to have specialized functions and these are known as organelles.
Specifically think of the membrane bound organelles that you have in your body. We are subjugating molecules and enzymes and proteins in that one organelle and giving that organelle a specific function. What that is basically doing is it's compartmentalizing the cell to have different organelles, to have different functions, so we can put all of the enzymes and proteins we need in that specific organelle. This optimizes the efficiency because we have all of the things that are needed for that specific function. We typically see this in eukaryotic cells since we have these membrane-bound organelles that have very specialized functions.
Prokaryotes really don't have these membrane-bound organelles like the eukaryotes do, but they also have specialized regions within the cell that do complete these processes. Something else about this compartmentalization that helps us with efficiency is something called a feedback inhibition. This is where a product at the end is going to inhibit an earlier reaction, thus regulating this process. Essentially, this is kind of like a negative feedback inhibition where a product here, D, is going to inhibit enzyme one here. That's going to inhibit the rest of this process since this is a linked series of events.
This helps a cell regulate itself and make it so it doesn't produce too much of a single product. That would be wasteful because those products could break down and not be used, and that's not efficient for a cell. Here's another way of looking at it.
You can see this series of linked reactions where we're changing this triangle into a rectangle, into whatever this blue shape is, into this square that's yellow. This end product then will inhibit this earlier step, stopping the substrate then from going through this series of linked reactions. It's a way to stop. the initial reaction to make sure the cell is efficient in regulating itself with how much product it's actually producing.
We also have this thing called a metabolic pathway disease, where again, we have this series of linked reactions with enzymes, and one of the enzymes along the pathway doesn't work correctly. There could be a bunch of different reasons why this doesn't occur correctly. There could be a gene mutation, there could be just a folding, you know, error in that protein, but for whatever reason, there's an enzyme that doesn't get produced correctly.
So what happens is E stops getting produced into F and then F can't be produced into G even though this enzyme still works. So there's almost a two-part problem here where we have an overabundance of this product E and underabundance of this product G. So sometimes this can cause two different problems where we have too much of E and not enough G. And we're going to end on this Drake meme.
A student made me this a couple years ago, and I thought this was fantastic. Cells love to be compartmentalized.