A common question in biology is – How do enzymes lower activation energy? If enzymes did not exist, our body would have to rely on them during reactions spontaneously. It would not be able to handle all of the waste products building up without being broken down.
For example, these reactions do not occur as fast enough for our body to cope with that alone. Waste products would build up in our body, and our digestive system would not be as efficient as it is without enzymes.
Activation energy is needed to break down chemical bonds allowing the reaction to occur. When an enzyme binds to a substrate, it lowers the substrate molecules’ energy to react to form products. This increases the chance of the reaction occurring and therefore increases the rate of reaction.
Not only do they lower the activation energy, but it also increases the possibility of the reaction. If the reaction were to happen spontaneously, an enzyme’s role is to lower the activation energy needed to start a reaction to proceed quickly without a temperature change.
Make sure that our body does not change in temperature. This is extremely important because, in cells, heat damage can make some a lot of damage to our living tissues.
For a chemical reaction to begin an activation, energy is necessary. So, the enzyme does not provide the activation energy. It only lowers the activation energy needed by bringing the specific molecules together rather than relying on them.
What is activation energy?
It is the amount of energy that we have the input for the reaction to convert the reactants to the products. Activation energy is simply the difference between the high molecule state’s energy and that reactant’s energy. This is called the Gibbs free energy, which Delta G gives.
The activation energy describes how quickly a reaction takes place so a reaction can be spontaneous. It can have a negative Delta G value, but it can take place very slowly if a reaction takes place very slowly, what that means. It means that it has very high activation energy.
So activation energy is not the same thing as Gibbs free energy. Gibbs free energy describes the difference between the energy of the reactants and the products. But activation energy explains how quickly a reaction takes place.
So Gibbs free energy talks about where that equilibrium will be achieved, while activation energy talks about how quickly the equilibrium will be achieved.
How do enzymes lower activation energy?
This lecture will look at how enzymes work and the process of enzymes lower activation energy. The enzyme reacts with substrate and makes the products, and the substrate is kind of complementary towards the enzymes active site.
Now, We are going to look at what is exactly happening while enzymes and substrates are interacting. We will look at the kinetic data, the thermodynamic and the structural aspect of this interaction.
Here is a graph that would help us to understand how enzymes and substrate work. In the X-axis of the graph, you have the reaction progression. It’s kind of like a time, and in the Y-axis, you have free energy change.
Now without any enzyme, if you add some substrate, it would be eventually become a product, but it would take a lot of time. The graph looks like this where you have the reactants’ energy as the initial part, and then eventually, it would get converted into the product.
The difference between the energy of the reactant and the transition state is the activation energy. So activation energy without the enzyme kind of looks like the black curve. If you have an enzyme that can catalyze this reaction, the graph looks like the red curve.
As you can notice, the activation energy has been reduced to start the reaction with the enzyme. This reduction in the activation energy is the key aspect of the enzyme-substrate reaction because it reduces the active activation energy. So what is activation energy?
- The difference between the ground state’s energy levels and the transition state can be defined as activation energy.
The enzyme and enzyme-substrate interaction decrease the react enzyme-substrate reaction’s activation energy and reaction rate.
- The enzyme does not change the equilibria. This is one of the most critical aspects of how enzymatic reactions work.
Now let’s try to understand things in bit more details and understand how enzyme specificity is brought about.
Here is an enzyme binding to this particular substrate, but this specific enzyme will not bind with another substrate. There is a mismatch, or this particular substrate is not fitting into the enzyme’s active site. And to understand all of these aspects, we need to look at the structural elements of these enzyme-substrate interactions and develop an x-ray crystallography technique.
Structural biology has flourished. It looks at the enzyme substrate-bound structure or the enzyme structure individually in an unbound situation, crystallises both of these confirmations, and follows a different crystallographic technique.
Scientists have found out how exactly enzyme-substrate works. They figured out that several principles are associated with the catalytic power and the specificity of the enzyme. So we are going to look at that in a moment.
There are two key principles:
- First of all, there is something called binding energy, which augments the enzyme-substrate interaction.
- There is something called stereospecificity of an enzyme occurring due to the 3d conformation of the enzymes active site.
Let’s talk about binding energy. So the energy that is derived from the enzyme-substrate interaction maybe it’s a weak interaction that is known as the binding energy.
Binding energy is the primary energy source used by the enzyme to lower the activation energy. So the key aspect of the enzyme-substrate reaction is that the enzyme reduces the activation energy for this reaction, thereby augmenting the rate.
The binding energy provides this. The substrate is bound with an enzyme. In the active site, there are several interactions. Non-covalent or equivalent interactions are forming in the active area.
For example, a hydrogen bond is formed between two particular residues between these two substrates and enzymes. That bond formation energy is contributing to the binding energy.
There is not only one interaction. There could be multiple different small interactions. Some are hydrogen bonds, and some are maybe hydrophobic interactions or Vander Waals interaction.
All summation of all these bond formation energies would contribute to the binding energy, which has excellent important implications. Now that gives the enzyme the catalytic power, and also, these weak interactions are optimised in the reactions transition state.
And it has to be remembered that enzymes conformation the active site conformation is complementary to the substrate not in the ground state. But in the transition state to understand that let us try to visualize this process.
This is the enzyme. Its active site is not complementary to the substrate’s stereospecificity. So the substrate first binds a site away to the active site, and multiple small interactions are happening between the enzyme and substrate.
But while the enzyme-substrate reaction is going through a transition state in that situation, the active site’s confirmation is also changed. It is induced by the initial weak interactions between the enzyme and substrate. It changes the active site’s conformation such that the substrate fits nicely in the enzyme’s active site.
This is the importance of binding energy. We learned from this that there is a loose binding of enzyme and substrate in the ground state, but the form binding occurs in the transition state only, which augments this process and lowers the activation energy. The binding energy is providing the energy to lower the activation energy. Thereby ultimately, the reaction can go on, and products are formed.
We also learned that the optimal interaction between substrate and enzyme occurs only in the transition state, not in the ground state.
Frequently asked questions
The enzyme does not change the Gibbs free energy of the reaction. It does not affect the energy of the reactants and the products. So their difference the Delta G is the same.
It remains unchanged when the enzyme acts on that chemical reaction, but it affects activation energy. The enzyme typically does that. It lowers that transition state’s energy by lowering the transition state’s energy.
– Enzymes do not affect equilibrium. They do not affect the Gibbs free energy of that reaction. The reactants’ thermal free energy and the free energy of products remain unchanged for any catalyzed reaction.
However, what the enzymes do is stabilize the transition state lower its energy. They lower the energy of that transition state, and so they decrease the activation energy. This speeds up that chemical reaction.
When they act on chemical reactions, enzymes do not change the Gibbs free energy, which means they do not increase or decrease how much products are formed at the end of that reaction. But they allow equilibrium to be achieved quicker by increasing the rate by reducing that activation energy.