This week we will talk about enzymes, those molecules that participate in almost the majority of the reactions that occur in any living cell. Despite having repeated the word enzyme in much of the post written so far, something that shows its great importance, we have never focused on talking specifically about them.
Today we will discuss, in more detail, what they are about, how they are classified and what they are used for… KEEP READING!
What are enzymes?
Enzymes are biocatalysts, that is, they are the catalysts of biological reactions. Considering that a catalyst is a substance that accelerates the course of a chemical reaction, a biocatalyst or enzyme is a substance that accelerates a biological reaction, which, without its presence, could take years to complete.
Therefore, the role of enzymes is the catalysis or acceleration of biological reactions, which occur in living beings. An example? Degrade the proteins in the meat we eat to absorb all its nutrients. This biological reaction would be carried out by a specific type of enzymes, present in our gastrointestinal tract: proteases.
In addition to accelerating the speed of a certain reaction, enzymes have another characteristic characteristic of any catalyst, whether biological or not, and that is that they are not consumed during the reaction. That is, the enzyme acts, and after conducting and accelerating one reaction it can re-catalyze another.
What enzymes do have that non-biological catalysts do have are characteristics such as high specificity, since each type of enzyme acts on a single reaction; that they always act at the temperature of the living being in which they are; and that they have a very high activity, managing to increase the reaction speed in more than a million times.
Why does an enzyme speed up a biological reaction?
What the enzyme does is lower the activation energy that is needed for such a reaction to start. And here I will tell you the typical simile that appears in school textbooks: if you want to throw an object, which is on the ground, for the sale, you first have to force yourself to lift the object to the edge of the sale, ¿ true?
That would be the activation energy. Once that energy is exceeded, the reaction proceeds, or the object falls from the window, quickly. If the more expensive stage is accelerated, the reaction generally occurs more quickly. That is the mission of any enzyme.
How do enzymes work?
Enzymes consist of a region called the active center, the part of the enzyme to which the substrate, the molecule on which the reaction will take place, binds, specifically and exclusively.
The formation of the enzyme-substrate complex creates an environment that promotes biological reaction, if we continue with the example of proteins, protein degradation. Once the protein has been broken down into smaller fragments, these leave the enzyme and it remains intact, being able to act again, breaking down another protein.
What determines that an enzyme only has specificity for a specific substrate and reaction?
The specificity between the enzyme and the substrate can be:
Absolute: If the enzyme only acts on a substrate.
Group: The enzyme works on a certain group of molecules.
Class: The enzyme recognizes and acts depending on a specific area of the substrate, and therefore does not depend on the type of molecule itself.
The substrate may fit into the active center of the enzyme like a key in your lock, it may have to change its shape to bind and form the enzyme-substrate complex, or both parts have to change their conformation. In both three cases, the enzyme-substrate interaction is carried out through specific links between both parties.
And watch out, because there are 3 factors that affect enzyme activity: temperature, pH and inhibitors. Normally, increasing the temperature increases the mobility of the molecules and therefore it is easier for the substrate and enzyme to meet and the reaction to take place. However, if we exceed a certain temperature, the enzyme breaks down and becomes unusable. Something similar happens with pH, since outside of limit values, enzymes do not work properly either.
And finally the inhibitors, substances that prevent or diminish the action of an enzyme. Why? Because having a very similar shape to the substrate, they bind to the enzyme, blocking its active center and preventing the entry of the true substrate and therefore, the reaction.
How are enzymes classified?
Enzymes are classified into six main classes, according to the general type of reaction in which they participate:
Oxidoreductases: Accelerate or catalyze oxidation and reduction reactions. An example would be oxidases and dehydrogenases.
Transferase: They are dedicated to transfer groups or radicals between different molecules, such as hexokinase.
Hydrolases: Break chemical bonds by adding a molecule of water. A clear example would be lysozyme.
Liases: They separate groups without the intervention of water (without hydrolysis), originate double bonds or add CO2, such as rubisco.
Isomerases: They perform conversions within the same molecule, such as triosaphosphate isomerase.
Ligasas: They catalyze the union of molecules or groups thanks to ATP, such as DNA-ligase.
Within each class there are groups, subgroups and series, so each enzyme is assigned a 4-digit number that identifies it. And I don’t know if you have noticed, but a large part of the enzymes end in -asa, a trick that can be useful to identify them. For example: the enzyme that breaks down lactose is called lactase and it is the enzyme that lactose intolerant does not possess. Or the protein-degrading enzyme, protease.
Although at the moment only about 3000 different enzymes have been described, it is estimated that up to 10,000 could exist in nature.
What are enzymes used for in our day to day?
They are part of products such as detergents, in which enzymes such as lipases or proteases are added to break down the food residues that form stains on our clothes. In addition, they are used in manufacturing processes such as cheese, in which renin is added to curdle milk. They are part of diagnostic kits in clinical tests, such as peroxidase. Or they are used for the synthesis of antibiotics among many other applications.
More related information?
Zymogens or proenzymes: Enzymes or ions that have the function of activating an enzyme.
Isoenzymes: They are different forms of the same enzyme that catalyze the same reaction but can be present at different stages of life or in different organs and tissues.
Enzymes can be classified into two types according to their composition:
If they are strictly proteinic.
Holoenzymes: they have a protein part and a non-protein part called a cofactor. These cofactors can be inorganic (ions) or organic, also called coenzymes such as ATP or coenzyme A.