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 handle all of the waste products without being broken down. For example, these reactions do not occur as fast enough for our bodies to cope with them alone. Waste products would build up in our body, and our digestive system would not be as efficient 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. It increases the chance of the reaction occurring and increases the reaction rate.
Not only do they lower the activation energy, but they also increase 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. It is extremely important because, in cells, heat damage can cause 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 activation energy. It lowers the activation energy needed by bringing the specific molecules together rather than relying on them.
What is activation energy?
The amount of energy we have the input for the reaction to convert the reactants to the products. Activation energy is 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 to be spontaneous. It can have a negative Delta G value but take place very slowly. If a reaction takes place very slowly, what does that mean? 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 enzymes lower activation energy. The enzyme reacts with the substrate and makes the products, and the substrate complements the enzyme’s active site.
Now, we will look at what exactly happens while enzymes and substrates interact. We will look at this interaction’s kinetic data, thermodynamics, and structural aspects.
Here is a graph that would help us understand how enzymes and substrate work. In the X-axis of the graph, you have the reaction progression. It’s like a time, and you have free energy change in the Y-axis.
Without any enzyme, if you add some substrate, it would eventually become a product, but it would take a lot of time. The graph looks like this: 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 looks like the black curve. The graph looks like the red curve if you have an enzyme that can catalyze this reaction.
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 activation energy and reaction rate.
- The enzyme does not change the equilibria. It is one of the most critical aspects of how enzymatic reactions work.
Now let’s try to understand things in more detail 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 specific substrate is not fitting into the enzyme’s active site. To understand 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, crystallizes both 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 enzyme’s catalytic power and specificity. So we are going to look at that in a moment.
There are two key principles:
- First, there is something called binding energy, which augments the enzyme-substrate interaction.
- The stereospecificity of an enzyme occurs due to the 3d conformation of the enzyme’s 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 contributes to the binding energy. There is not only one interaction. There could be multiple different small interactions. Some are hydrogen bonds, and some may be hydrophobic or Vander Waals interactions.
All summation of these bond formation energies would contribute to the binding energy, with excellent important implications. Now that gives the enzyme the catalytic power. These weak interactions are optimized in the reaction’s transition state. It must be remembered that enzymes conformation the active site conformation to complement the substrate, not in the ground state. But in the transition state, let us try to visualize this process.
It is the enzyme. Its active site is not complementary to the substrate’s stereospecificity. So the substrate first binds a site away from the active site, and multiple small interactions occur 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.
It 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 only occurs in the transition state, which augments this process and lowers the activation energy. The binding energy provides 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 the ground state.
Frequently asked questions
How does the enzyme affect the activation energy?
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 in the Delta G is the same.
It remains unchanged when the enzyme acts on that chemical reaction but affects activation energy. The enzyme typically does that. It lowers that transition state’s energy by lowering its 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, the enzymes stabilize the transition state and lower its energy. They lower the energy of that transition state, decreasing the activation energy. It 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 many 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.
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Sources:
Stryer L, Berg JM, Tymoczko JL. Biochemistry (5th ed.). San Francisco: W.H. Freeman.
Murphy JM, Farhan H, Eyers. “Bio-Zombie: the rise of pseudoenzymes in biology.” Biochem Soc Trans.
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