Enzymes: what they are, examples and classification

Enzymes are proteins that catalyze chemical reactions which occur in living beings.

They 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 also not consumed. Thus, they can participate several times in the same type of reaction, 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 high. It is estimated that, in general, an enzyme molecule is capable of converting 1000 substrate molecules into their respective products, this in just 1 minute.

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 generically called

substrate. The great enzyme-substrate specificity is related to the three-dimensional shape of both.

The enzyme binds to a substrate molecule in a specific region called link site. For this, both the enzyme and the substrate undergo a change in conformation for the fitting.

They fit perfectly like keys in locks. This behavior is called Key-Lock Theory.

Operation of the Key-Lock model

Among the factors that alter the activity of enzymes are:

• Temperature: Temperature conditions the reaction rate. Extremely high temperatures can denature enzymes. Each enzyme works at an ideal temperature.
• pH: Each enzyme has a pH range considered ideal. Within these values ​​the activity is maximum.
• Time: The longer the enzyme has contact with the substrate, the more products will be produced.
• Enzyme and substrate concentration: The higher the concentration of enzyme and substrate, the faster the reaction will be.

Classification

Enzymes are classified into the following groups, according to the type of chemical reaction they catalyze:

1. Oxido-reductases: oxidation-reduction or electron transfer reactions. Example: Dehydrogenases and Oxidases.
2. Transferases: transfer of functional groups such as amine, phosphate, acyl and carboxy. Example: Kinases and Transaminases.
3. Hydrolases: covalent bond hydrolysis reactions. Example: Peptidases.
4. Liases: Covalent bond breaking reactions and the removal of water, ammonia and carbon dioxide molecules. Example: Dehydratases and Decarboxylases.
5. Isomerases: interconversion reactions between optical or geometric isomers. Example: Epimerases.
6. Ligases: reactions of formation of new molecules from the link between two pre-existing ones. Example: Synthetases.

Examples and Types

Enzymes are formed by a protein part, called the apoenzyme and another non-protein part, called the cofactor.

When the cofactor is an organic molecule, it is called coenzyme. Many coenzymes are related to vitamins.

The enzyme + cofactor set is called holoenzyme.

See some of the main enzymes and their actions:

• catalase: decomposes hydrogen peroxide;
• DNA polymerase or reverse transcriptase: catalyzes DNA duplication;
• lactase: facilitates lactose hydrolysis;
• Lipase: facilitates lipid digestion;
• Protease: act on proteins;
• urease: facilitates urea degradation;
• Pthyalin or Amylase: acts on the degradation of starch in the mouth, transforming it into maltose (smallest molecule);
• Pepsin or Protease: acts on proteins, degrading them into smaller molecules;
• Trypsin: participates in the breakdown of undigested proteins in the stomach.

Restriction Enzymes

Restriction enzymes or restriction endonucleases are produced by bacteria.

They are able to cut DNA at specific points.

We can consider them molecular scissors. Restriction enzymes are fundamental to the manipulation of DNA.

Also know about recombinant DNA.

Ribozymes

Ribozymes are RNA molecules that act like enzymes. Many chemical reactions that take place inside cells are catalyzed by RNA.

Like proteins that act as enzymes, these RNA molecules accelerate the speed of certain chemical reactions.

They are also highly substrate specific and remain chemically intact after the reaction.

The performance of these ribozymes is linked to various stages of protein synthesis in the cells.

Also read about:

• Cell Metabolism
• Digestion