Enzyme Activation Energy - Online Tutor, Practice Problems & Exam Prep

Activation energy (EA) is the minimum energy required to initiate a chemical reaction, defined as the energy difference between reactants and the transition state. Enzymes lower this activation energy, facilitating faster reactions. In exergonic reactions, the reactants possess higher energy than the products. The transition state represents a temporary peak energy state. Lowering the activation energy through enzymatic catalysis significantly accelerates reaction rates, highlighting the crucial role of enzymes in biochemical processes.

Enzyme Activation Energy

In this video, we're going to begin our lesson on the enzyme activation energy. And so the activation energy is sometimes called the energy of activation, and it's commonly abbreviated as just Ea. And so the activation energy or energy of activation or Ea is really defined as the difference in energy between the reactants of a reaction and the transition state of a reaction. Now we'll define the transition state here very, very shortly. But first, focusing in on the activation energy or the Ea, the Ea or the activation energy represents the minimum amount of energy that's required to start a chemical reaction.

Now all reactions have an activation energy, and that includes both exergonic and endergonic reactions. And so the higher the energy of activation is, the slower the reaction will be. And so the energy of activation is really just going to dictate the speed that the reaction will occur. The higher the reaction energy of activation is, the slower the reaction will take place. And so the lower the energy of activation is, the faster the reaction will take place.

Now the transition state is defined as a temporary state of maximum energy within a reaction. And so let's take a look at our image down below to start to clear some of this stuff up. And so notice that we're showing you this graph down below where on the y-axis we have the free energy and on the x-axis we have the reaction progress or the time as the reaction proceeds. And so notice that we're starting off with some reactants and the reactants have higher free energy than the products which are down below which have lower free energy. And so that makes this an exergonic reaction.

And so we can label the reactants as having higher energy than the products which have low energy. And so notice that the transition state again is going to be a temporary state of maximum energy in a reaction. And so where there is maximum energy is at the peak of this curve here. And so at the very, very peak is where we will find the transition state. And so we can label this as the transition state.

And so the activation energy, recall, is defined as the difference in energy between the reactants and the transition state. And so if we find the reactants, notice the reactants are right here and the transition state is right here. And so the difference in energy between the two is going to be represented by this region that is right here, the activation energy. And so we can label the activation energy, which is shown by this yellow bar here. The activation energy is abbreviated as Ea, and it's going to represent the minimum amount of energy required to start the chemical reaction.

And so even in an exergonic reaction like this, there is a minimum amount of energy that needs to be overcome in order for the reaction to proceed. And so this here is showing how the activation energy is represented by this difference in energy between the transition state and the reactants, and the activation energy is going to determine the speed of the reaction. The higher the activation energy is, the slower the reaction will be. And so now that we better understand the activation energy or Ea, in our next video, we'll talk about how enzymes affect the activation energy. So I'll see you all in that video.

Enzymes Lower Activation Energy

So now that we've introduced the activation energy in our last lesson video, in this video we're going to talk about how enzymes affect the activation energy of chemical reactions and more specifically how enzymes will lower the activation energy. And so once again, enzymes catalyze chemical reactions by lowering their activation energy barrier or essentially lowering the transition state energy. Now reactions are going to occur much, much faster in the presence of an enzyme because the activation energy has been lowered. And remember, the lower the activation energy, the faster the reaction. The higher the activation energy, the slower the reaction.

And so let's take a look at our example down below to clear some of this up, looking at the reaction coordinate for enzymatic catalysis. And so once again, we've got this graph where we got the free energy on the y-axis and the reaction progress on the x-axis or the time as the reaction progresses. And so notice that we're showing an exergonic reaction because the reactants have higher energy than the products, which have lower energy. And so notice that the activation energy is being represented in two different ways here in this image, and that's because we have two different curves. We have this blue curve that you can see right here, and then we also have this red curve that you can see right here.

And so the blue curve corresponds with the enzymatic reaction without an enzyme. And so you can see that the energy of activation without the enzyme is quite large. You can see that it's going to be the difference in the energy between the reactants and the transition state for the blue curve, which is, this large, blue arrow that you see right here. And this is again without an enzyme. So notice that the activation energy is large and that makes the reaction slow.

But then notice that with the red curve right here, this represents the same exact chemical reaction except in the presence of an enzyme with an enzyme being present. And so notice that the red curve here has a much smaller activation energy. You can see it's shorter in comparison to the activation energy without an enzyme. And so because the activation energy is smaller with an enzyme, that makes the reaction occur much, much faster. And so, you can see that the transition state here for the reaction in the presence of an enzyme with an enzyme is much much lower.

And so that makes the activation energy lower and that ends up making the reaction proceed faster in the presence of an enzyme. So really the main takeaway here of this video is that enzymes speed up chemical reactions by lowering the energy of activation. And so this here concludes our video and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Which of the following statements is TRUE regarding an enzyme's function?

• A. It is generally increased if the structure or conformation of an enzyme is altered.
• B. It is independent of factors such as pH and temperature.
• C. It increases the rate of chemical reactions by lowering activation energy barriers.

Here’s what students ask on this topic:

What is activation energy and why is it important in chemical reactions?

Activation energy (Ea) is the minimum amount of energy required to initiate a chemical reaction. It is defined as the energy difference between the reactants and the transition state. This energy barrier must be overcome for reactants to be converted into products. Activation energy is crucial because it determines the rate at which a reaction will occur. Higher activation energy means a slower reaction, while lower activation energy results in a faster reaction. Understanding activation energy helps in controlling and optimizing reaction conditions in various biochemical and industrial processes.

How do enzymes lower activation energy in biochemical reactions?

Enzymes lower the activation energy (Ea) of biochemical reactions by stabilizing the transition state and reducing the energy barrier that must be overcome for the reaction to proceed. This is achieved through various mechanisms, such as providing an alternative reaction pathway, bringing reactants into close proximity, and properly orienting them for the reaction. By lowering the activation energy, enzymes significantly increase the reaction rate, allowing biochemical processes to occur rapidly and efficiently under physiological conditions.

What is the transition state in a chemical reaction?

The transition state in a chemical reaction is a temporary, high-energy state that occurs during the conversion of reactants to products. It represents the point at which the reactants have absorbed enough energy to break their bonds and form new ones, leading to the formation of products. The transition state is characterized by maximum energy, and it is the peak of the energy barrier that must be overcome for the reaction to proceed. Understanding the transition state is essential for studying reaction mechanisms and the role of catalysts like enzymes.

How does the activation energy affect the speed of a chemical reaction?

The activation energy (Ea) directly affects the speed of a chemical reaction. A higher activation energy means that more energy is required to initiate the reaction, resulting in a slower reaction rate. Conversely, a lower activation energy means that less energy is needed, leading to a faster reaction rate. Enzymes and other catalysts work by lowering the activation energy, thereby increasing the reaction speed. This relationship is crucial for understanding how reactions can be controlled and optimized in various scientific and industrial applications.

What is the difference between exergonic and endergonic reactions in terms of activation energy?

Exergonic and endergonic reactions differ in their energy profiles but both require activation energy (Ea) to proceed. In exergonic reactions, the reactants have higher free energy than the products, and the reaction releases energy. Despite this, an initial input of activation energy is still needed to reach the transition state. In endergonic reactions, the reactants have lower free energy than the products, and the reaction absorbs energy. These reactions also require activation energy to reach the transition state. The key difference lies in the overall energy change: exergonic reactions release energy, while endergonic reactions absorb it.