Proteins and enzymes are two closely related names that are often misused. Both refer to biological macromolecules but the definition of each is based on different criteria . The proteins are defined based on its chemical composition , while the enzymes are defined based on its function :
- Protein : is a biological macromolecule formed by one or more chains of amino acids.
- Enzyme : is a biological macromolecule that catalyzes biological reactions.
Proteins have numerous functions; these are:to transport substances between organs and between the outside and inside the cell, they form antibodies for the immune system, form the membrane receptors and many signaling substances, and regulation of hormones.
Another function of proteins, one of the most important and best known, is the catalysis of biological reactions ; the proteins that have this function are those that act like enzymes. Practically 100% of the metabolic processes require the participation of enzymes to run at a rate sufficient to sustain life .
It is very common that enzymes are understood as proteins with catalytic function, but this is not always the case. Not all enzymes are proteins ; there are other biological macromolecules with catalytic action.
Until 1982 all known enzymes were proteins, and all proteins are the result of DNA transcription, a process in which RNA is formed which is subsequently translated into proteins. That year ribozymes , ribonucleic acid (RNA) molecules with catalytic function were discovered .
The discovery of ribozymes was the first evidence that nucleotides , the basic unit of genetics, are not mere passive carriers of information , the catalytic role of ribozymes is essential for life, and therefore play an active role. Thomas Cech and Sidney Altman won the Nobel Prize in chemistry in 1989 for the discovery of ribozymes.
Catalysis is defined as the increase in the speed of a chemical reaction caused by the participation of another substance other than the substrates and products. This third substance is called the catalyst and is able to decrease the activation energy of a given reaction, which allows a higher speed without increasing the temperature .
Enzymatic catalysis participates in almost 100% of the metabolic reactions that occur in the cellular interior. Some enzymes increase the rate of reaction millions of times ; some reactions that would not occur in thousands of years, occur in a few milliseconds inside the cell. Without the presence of enzymes these reactions would be too slow to sustain life.
Enzymatic proteins are very numerous. Almost all are of the globular type but are very heterogeneous and variable in size. They can act alone or as part of enzymatic complexes in which other proteins and other substances, for example metal ions, participate.
Ribozymes ( ribonucleic acid enzymes ), on the other hand, are molecules formed by a chain of nucleotides and catalyze very specific reactions related to RNA processing and protein synthesis . Like enzyme proteins, ribozymes can act alone or in association with proteins in enzymatic complexes.
Many ribozymes are autocatalytic introns (one part of the molecule catalyzes a reaction in another part of the same molecule). Among the reactions that catalyze ribozymes stand out the maturation of tRNA and transpeptidation .
The fact that RNA can act as genetic material that transmits information and as biological catalysts is a strong argument in the hypothesis of the world of RNA , one of the main hypothesis of abiogenesis (orgien of life). According to this hypothesis, RNA molecules that could duplicate themselves could be at the origin of life, probably in the form of viroids whose evolution would lead to the first prokaryotic cells.
The two key differences
- Proteins are molecules formed by chains of amino acids and includes numerous enzymatic activity ; other proteins have transport, structural, hormonal, immunological, etc. activity.
- The enzymes are molecules with catalytic function and almost all known are proteins. The ribozymes are formed by nucleotides ribonucleic acid enzymes.