Enzyme Substrate Complex: Definition and Example

Enzyme Substrate Complex Definition

The enzyme-substrate complex is a temporary molecule formed when an enzyme comes into perfect contact with its substrate. Without its substrate, an enzyme is in a slightly different shape. The substrate causes a conformational change, or shape change when the substrate enters the active site. The active site is the area of the enzyme capable of forming weak bonds with the substrate. This shape change can force two or more substrate molecules together, or split individual molecules into smaller parts. Most reactions that cells use to stay alive require the actions of enzymes to happen fast enough to be useful. These enzymes are directly coded in the DNA of the organism.

The enzyme-substrate complex is extremely important for a number of reasons. First, the enzyme-substrate complex is only temporary. This means that once the substrate has changed, it can no longer bind to the enzyme. The products are released and the enzyme is ready for another substrate molecule. A single enzyme can operate repeatedly millions of times, meaning only a small amount of enzyme is needed in each cell.

Enzymes are complex molecules, like little machines meant for one purpose. Built out of a chain of amino acids, this long string experiences interactions between the different amino acids and twists and turns into complex structures. These structures can operate like hinges, wedges, and all sorts of other shapes intended to speed certain reactions. Different mutations give rise to slightly different forms of the enzyme. In mutations that are beneficial to the organism, the enzyme-substrate complex is changed in a way that affects the output of the product or the function of the enzyme as a whole. This change in the organism is only beneficial if it somehow helps the organism reproduce more.

Enzymes are usually named after the substrate that they work on, and have the -ase suffix to designate they are enzymes. Each enzyme has a certain specificity for the substrate it works on, which determines which molecules it can bind to. Some molecules that are similar in structure to the substrate may get stuck in the active site, because they cannot undergo the reaction intended by the enzyme. In this warped enzyme-substrate complex, the competitive inhibitor binds to the enzyme and inhibits its further action. Other inhibitors do not copy the substrate but modify the enzyme in other ways so the enzyme-substrate complex cannot be formed.

Examples of Enzyme Substrate Complex

Amylase and Amylose

Amylose is a complex sugar produced by plants. In our saliva is an enzyme, amylase, used to break amylose apart. Amylase uses one substrate molecule of amylose and a cofactor of one water molecule to produce an enzyme-substrate complex. The complex severely reduces the amount of energy required to start the reaction, which increases the time in which it happens. A typical sugar molecule would take millions of years to break apart, were it not for the actions of enzymes such as amylase.

In fact, enzymes are so important in digesting the foods we eat that our body produces an enzyme for almost every type of food the body is evolutionarily prepared to consume. New foods are poorly processed because the enzymes have not had time to adjust their efficiency. For instance, the modern diet of processed foods is leading to an obesity epidemic because processed foods are rich in easily accessible nutrients, but only to the pathways that are used to store fat. As a result, much of the population experiences weight-related illnesses. Many nutritionists are pushing for more natural, whole-food, plant-based diets that tend to support the enzymes our bodies have naturally developed.

Allosteric Regulation in Enzymes

Although the enzyme-substrate complex forming quickly is important for most reactions, in some cases it is important to “turn off” the enzyme to conserve energy or resources. Many enzymes are regulated in this way to provide just the right amount of energy and products. One of the most important places this happens is in the production of adenosine triphosphate (ATP), or the molecule that provides energy to cellular processes. Many of the enzymes in the pathway that creates ATP are inactivated by ATP. In this way, when too much ATP is produced, the enzyme shuts off. This is known as feedback inhibition, or the ability to self-regulate. In the same way, the enzymes can be reactivated by the presence of adenosine diphosphate ADP, an ATP that has used a phosphate group to provide energy to a process or reaction.

Many bodily processes are controlled in this manner, and the enzyme-substrate complex in these cases can only be formed with the proper molecules present. Many of the cofactors that activate enzymes are vitamins, minerals, and other inorganic molecules present in the diet.

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