There is a conditional division of proteins into products and organisms into subspecies::

1. Peptides (polypeptides) protein compounds of 2 to several ten residual amino acids in length, which are formed by the condensation of amino acids.
2. Free (Unbound) amino acids are completely cleaved protein molecules, which are isolated substances or complex compounds.
3. Proteins are substances with a higher degree of polymerization. A separate class of proteins are enzymes that are biological catalysts. These substances contribute to the multiple acceleration of biochemical reactions in the body.

Protein functions:
catalytic - helps to accelerate biochemical reactions (synthesis or cleavage of molecules, etc.).). This function is provided by special proteins - enzymes contained in foods and produced by the body.
Energy - is responsible for the energy production during the degradation of proteins and is activated only when other energy sources (fats and carbohydrates) are consumed.
Protection - protects body at the physical level (blood clotting, maintaining the normal state of connective tissue and epidermis), chemical (neutralization of toxins) and immune defense (forms a reaction to the effects of pathogenic microorganisms or damage, neutralizes viruses and bacteria, etc.).
structural (construction) - manifests itself in the formation of cells and a change in their shape.
Regulatory - regulates the activity of a number of proteins, promoting cell structures in a cycle and other processes (e.g. stimulating the formation of fats from carbohydrates, regulating blood sugar levels, etc.).).
signal - is responsible for the transmission of intercellular and interstitial signals.
transport - provides Transport of small molecules (oxygen, carbon dioxide, etc.) within the body as well as from cells into space and vice versa.
reserve - forms a stock of certain proteins that serve as energy sources or amino acid sources.
receptor - used to receive signals (mechanical effects, chemicals, light, etc.) and transmit them to other cellular components.
Movement capability - provides the processes of movement in the body (intracellular transport, movement of cells, muscle contraction, etc.).