In this video, we're going to introduce yet another way that cells can regulate their biochemical reactions, and that is through negative feedback. And so negative feedback is also sometimes referred to as just feedback inhibition. And so negative feedback or feedback inhibition is an efficient and a very common means for biochemical regulation. And so cells use negative feedback all the time to regulate their reactions. Now really the purpose of negative feedback is to prevent the overproduction as well as the wasteful production of a product. And so as we'll see moving forward, negative feedback is really just a way for molecules such as a product to regulate the production of its own activity. And so negative feedback inhibition is when the final product or just a later product in a metabolic pathway can come back and inhibit an earlier step in the same exact metabolic pathway that led to that product's production. And so ultimately, this is going to slow down the entire metabolic pathway, and that is going to begin to decrease the final concentration of that product that acted to inhibit the reaction. And so, as we'll see down below in our example, negative feedback inhibitors really do, inhibitors, really do act as inhibitors. And recall that inhibitors are commonly represented with a negative symbol. And so these negative feedback inhibitors are going to bind to an allosteric an allosteric site on the allosteric enzyme and of course that means that it's not going to bind to the enzyme's active site. And so down below in our example, notice we're saying that negative feedback inhibition really acts like the red light, to inhibit metabolic pathways. And so over here what we have is a red light to show you that, really negative feedback acts like a red light and slows down these, metabolic pathways. And so over here we're showing you an example of a metabolic pathway. And so you can see that we have all of these reactions here and notice that most of these reactions are being catalyzed by Michaelis Menten enzymes. But here we do have one enzyme that is displaying allosteric kinetics. And so, notice here that we have a final product f and if the concentration of f happens to get way too high, then f can actually come back and inhibit the allosteric enzyme number 1 here. And we know that it's inhibiting because, again, we have a minus sign here, that represents inhibition. And so if f comes all the way back to inhibit enzyme number 1, then that's going to prevent the conversion from a to b. And, ultimately, that's going to lead to the decrease of the concentration of product f. And so when the final concentration of the product f over here is returned back to normal or lower levels, then, the feedback inhibition that is caused by product f here is essentially going to stop, and that's going to allow the metabolic pathway to proceed once again. And so, clearly here we're talking about negative feedback inhibition. And you can see how really through negative feedback inhibition, molecules such as product f here are able to regulate their own production. And so, by coming back and inhibiting enzyme number 1, product f can influence the decrease or the lowering of its concentration. And so, it turns out again that negative feedback inhibition is an efficient and a common means for biochemical regulation. So later in our course we're going to talk about many different examples of negative feedback. And in our next lesson video, we'll specifically talk about one particular example. And so, I'll see you guys in that video.
Negative Feedback - Online Tutor, Practice Problems & Exam Prep
Negative Feedback
Video transcript
Negative Feedback Example 1
Video transcript
So now that we've covered the basics of negative feedback or feedback inhibition, in this video we're going to cover an example of feedback regulation in glycolysis. And so recall from your previous biology courses that glycolysis is just a process in cellular respiration that breaks down glucose to generate energy in the form of ATP. Notice in the image below, we're showing you a snippet of the glycolysis process or metabolic pathway. Over here on the far left, notice we are starting with a glucose molecule. One of the final products of glycolysis is the net generation of ATP. We're not showing the full glycolysis metabolic pathway here, but we will cover it later in our course. For now, we just want to emphasize that the cell already has plenty of ATP. And in that scenario, the cell would not want to be breaking down glucose to generate even more ATP. In this scenario, ATP can act as a negative feedback regulator to inhibit one of the enzymes that act in glycolysis, and this enzyme is known as phosphofructokinase, abbreviated as PFK. Phosphofructokinase or PFK is an allosteric enzyme that catalyzes a particular reaction in glycolysis. If we look below, notice that PFK catalyzes the conversion of fructose 6-phosphate into fructose 1,6-bisphosphate, essentially adding an extra phosphate group at this position. It needs to utilize ATP here as a co-substrate to catalyze this reaction. Again, PFK is going to be regulated via negative feedback by ATP. ATP can come back and negatively regulate PFK to inhibit it, essentially leading to the decrease of ATP or preventing the production of ATP. Because ATP is also utilized as a co-substrate for PFK, and ATP also acts as a negative allosteric regulator of PFK, that actually makes ATP a homotrophic allosteric effector. And that's because ATP is used as a substrate as well as an allosteric effector. Because the substrate is the same as the allosteric effector, that makes the allosteric effector homotrophic. This is just one example of negative feedback in glycolysis, but later in our course, we'll talk about a lot more examples of negative feedback throughout all of cellular respiration. But for now, this concludes our example of feedback regulation in glycolysis, and in our next video, we will be able to get some practice utilizing the concepts that we've learned. So I'll see you guys in that video.
The scheme below represents a hypothetical metabolic pathway for the synthesis of compound Y. The pathway is regulated by feedback inhibition. If S → T is the rate-limiting step, circle what the most likely inhibitor is and indicate with an arrow where the inhibition most likely occurs:
S → T → U → V → W → X → Y
Problem Transcript
Which of the following is TRUE about feedback inhibition?