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Question Video: Identifying the Activation Energy of an Enzyme-Controlled Reaction Biology

The graph provided shows the reaction profile of a biological reaction. Which letter indicates the activation energy?

02:15

Video Transcript

The graph provided shows the reaction profile of a biological reaction. Which letter indicates the activation energy?

In order to answer this question, let us review what a reaction is, what activation energy means, and how this is graphed in an energy diagram.

A reaction, such as this chemical one, starts with reactants. Something happens which will change the reactants and form a product or products. In this example, the reactants are two hydrogen molecules and one oxygen molecule. They will react together to form the product: two water molecules.

A reaction can happen more or less spontaneously, depending on how high the activation energy needed for it is. The activation energy refers to the minimum amount of energy required for a reaction to occur. Enzymes work by lowering the activation energy so that the reaction can proceed at a faster rate. Let’s have a look at the graph to understand this more properly.

We start at the beginning of a reaction in progress on the left-hand side of the graph. Let’s imagine that the reactant of this reaction is a large boulder, and we want to produce smaller pebbles. π‘Š is referring to the free energy of the reactants for this particular reaction. In our example, that would be the free energy of the boulder. In order to break the boulder up into smaller pieces, we need to add energy. This could be done by banging on it with a hammer or by transporting it up a steep hill from which we can drop it into the deep.

𝑋 is referring to this amount of energy required for the reactants to be converted into their products, and this is the value that enzymes lower as biological catalysts. This energy is called activation energy. π‘Œ shows the free energy change between the reactants and their products, since 𝑍 is referring to the free energy of the products themselves.

Now that we have reviewed our graph, we are able to answer our question. The answer to our question about which letter indicates the activation energy is 𝑋 since it refers to the minimum amount of energy required for the reactants to be converted into their products. Therefore, the correct answer is 𝑋.

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