Enzymes are proteins that catalyze chemical reactions that take place in living beings.
Characteristics
- Enzymes accelerate the speed of reactions, which contributes to metabolism. Without enzymes, many reactions would be extremely slow.
- During the reaction, the enzymes do not change their composition and are not consumed. In this way, they can participate in the same type of reaction several times, in a short period of time.
- Almost all cellular metabolism reactions are catalyzed by enzymes.
- An example of enzyme activity occurs in the digestion process. Thanks to the action of digestive enzymes, food molecules are broken down into simpler substances.
- The efficiency of an enzyme molecule is very great. It is estimated that, in general, one enzyme molecule is capable of converting 1000 substrate molecules into their respective products, that in just 1 minute.
- Almost all enzymes are of protein origin, with the exception of some catalytic RNAs. Some of them work without adding any other molecule to their polypeptide chain, others need to connect to another group, which we call cofactor, inorganic ions, or to a group of organic molecules that we call coenzyme (folic acid, vitamins, for example).
- In some cases, it can bind to both types and in others it can undergo alterations through processes such as glycosylation or phosphorylation.
- Each enzyme is unique for a given reaction. For its effective functioning, it must have its three-dimensional structure preserved (tertiary and quaternary).
- The conformation of this region forms a perfect and unique fit between a given enzyme and a substrate, usually by transient covalent junctions. At the end of the reaction it is released from the substrate and continues with its shape for new activities.
- Like any protein, it can denature under some conditions, such as high temperatures, extreme variation in pH, thus losing its function. Like all proteins, they need an ideal temperature and pH to activate reactions.
- The enzyme acts by varying the entropy of the reaction, directing the substrate so that it does not collide randomly, increasing the efficiency of the reaction.
- It also decreases the activation energy, without altering its balance. The regulation of enzymatic activity can be controlled by the cell itself, in protein coding, as well as by itself, varying according to some molecule that binds to it.
How do they work?
Each enzyme is specific for a type of reaction. That is, they act only on a certain compound and always carry out the same type of reaction.
The compound on which the enzyme acts is generally called a substrate. The great enzyme-substrate specificity is linked to the three-dimensional appearance that both present.
The enzyme binds to a substrate molecule in a specific region called the binding site. To do this, both the enzyme and the substrate undergo a conformational change to fit.
These fit perfectly like keys in locks. This behavior is called Key-Lock Theory.
Among the factors that alter the activity of enzymes are:
- Temperature: Temperature determines the reaction speed. Extremely high temperatures can denature enzymes. Each enzyme acts under an ideal temperature.
- pH: Each enzyme has a pH range that is considered ideal. Within these values the activity is maximum.
- Time: The longer the enzyme is in contact with the substrate, the more products will be produced.
- Concentration of the enzyme and substrate: The higher the concentration of the enzyme and substrate, the faster the reaction rate.
Classification
Enzymes are classified into the following groups, depending on the type of chemical reaction they catalyze:
- Oxidoreductases: oxidation and reduction reactions or electron transfer. Example: Dehydrogenases and Oxidases.
- Transferases: transfer of functional groups such as amine, phosphate, acyl and carboxy. Example: Kinases and Transaminases.
- Hydrolases: covalent bonding hydrolysis reactions. Example: Peptidases.
- Lyases: reactions that break covalent connections and eliminate water, ammonia and carbon dioxide molecules. Example: Dehydratases and decarboxylase.
- Isomerases: interconversion reactions between optical or geometric isomers. Example: Epimerases.
- Ligases: reactions to form new molecules from the bond between two pre-existing ones. Example: Synthetases.
Examples and Types
Enzymes are made up of a protein part, called apoenzyme, and another non-protein part, called cofactor. When the cofactor is an organic molecule, it is called a coenzyme. Many coenzymes are related to vitamins. The whole enzyme + cofactor is called a holoenzyme.
Some of the main enzymes and their functions:
- Catalase: breaks down hydrogen peroxide.
- DNA polymerase or reverse transcriptase: catalyzes the duplication of DNA.
- Lactase: facilitates the hydrolysis of lactose.
- Lipase: facilitates lipid digestion.
- Protease: act on proteins.
- Urease: helps in the urea degradation process.
- Amylase or Ptyalin: acts in the degradation of the starch found in the mouth, converting it into maltose (smaller molecule).
- Pepsin or Protease: acts on proteins, breaking them down into smaller molecules.
- Trypsin: participates in the degradation of proteins that have not been digested in the stomach.