What is a transition state? a. the shape adopted by an enzyme that has an inhibitory molecule bound at its active site b. the amount of kinetic energy required for a reaction to proceed c. the intermediate complex formed as covalent bonds in the reactants are being broken and re-formed during a reaction d. the enzyme shape after binding an allosteric regulatory molecule

Video transcript

Welcome back. Here's our next problem and the energy diagram for a biological reaction, identify the correct labeling for capitals, A. B. And C. So we have our reaction energy diagram here with three different levels here labeled on the diagram or the energy levels of the reactant and products. Um But we have this third level at the high point of the curve labeled as capital A. And we recall for a reaction to take place. Our reactant need to be um the chemical bonds need to be broken to form the new bonds in the products. And so the reactant molecules have to be sort of bent or deformed to put strain on those bonds and break them. So that state in which they are, you know, having their shape sort of contorted. Is this very unstable high energy state called the transition state. So this point here at this highest energy level of this reaction will be the transition state of the reaction. So the energy level energy amount needed to reach that transition state which is labeled here as capital B. Is as we can recall learning from a condom videos, it's called the activation energy. The activation energy is that amount of energy that needs to be put in for the reactors to reach that transition state in order for the reaction to proceed. So even if we're going to have a net gain of energy at the end, we have to put a little extra boost of energy um to allow that reaction to proceed. And that's called the activation energy. So we see two curves here with two different activation energies and we can recall as we've learned, what is it? That lowers this activation energy because this red curve has a lower activation energy. Lower energy in the transition state. Well, that's also an activation energy. As you can see, it's the high point of energy needed. But this would be in the presence of a catalyst or with a catalyst. And the catalyst is an enzyme. So the enzyme by having this specifically shaped active site that binds to the reactant and then can slightly change their shape. It helps to stabilize that transition state means less energy has to be put in to reach the transition state and therefore the activation energy for the reaction will be lower. So this lower curve is the activation energy with an enzyme meaning on our original curve, the original activation energy is without an enzyme. Just the reaction had to proceed by itself. So we have this uh point at the top of the curve labeled capital A. At the transition state. The energy needed to reach that point labeled capital B. Is the activation energy without an enzyme. And then on our lower curve, the energy needed to reach that new lower activation energy is the activation energy with with an enzyme. So let's look over answers and see which ones are labeled properly. Well, first of all, we know that Capital A. Needs to be transition state. So Choice A. And Choice B. Both have that properly labeled, but Choice C. And Choice D. Have capital A. Labeled as an activation state, which is not the correct terminology. So we can eliminate them. Capital B. We know is the activation energy without an enzyme. So Choice A. Says capital B activation energy and the absence of an enzyme. That is correct. But Choice B says letter B is activation energy in the presence of an enzyme and that is not correct. So we can eliminate Choice B. So we've just got a left. We'll just double check. Make sure C. Is labeled correctly. And in choice A letter C. Is labeled activation energy in the presence of an enzyme, which is correct. So we know that choice A must be our correct answer. So in the energy diagram for the biological reaction given here the correct labeling for A. B. And C. Is choice A. A. Is the letter is the transition state. Letter B. Is the activation energy in the absence of an enzyme. And let her see the activation energy in the presence of an enzyme. Hope to see you in the next video