We explain what proteins are and the types of proteins that exist. What are they for, their structural levels, and food?
What is Protein?
Proteins are macromolecules made up of structural units called amino acids. They always contain carbon, oxygen, nitrogen, hydrogen, and often also sulfur in their structure.
Amino acids are organic molecules composed of an amino functional group (-NH2) at one end and an active carboxyl group (-COOH) at the other. There are twenty essential amino acids, which in different combinations, constitute the basis of proteins. Two examples of amino acids are alanine and cysteine:
To form proteins, amino acids are joined together by peptide bonds, that is, the union of the end with the amino functional group (-NH2) of one amino acid, with the future that contains the active carboxyl group (-COOH) of another amino acid. Thus, the amino acids are linked in different combinations and as many times as necessary until each specific protein is formed. An example of how the peptide bond is started can be seen in the following figure, where an alanine is represented in pink, cysteine in red, and the peptide bond in blue:
Proteins are essential for the organism since they participate in all its processes. They can be classified according to the following:
It’s chemical composition:
Simple proteins. Also known as holoproteins, they are made up only of amino acids or their derivatives.
Conjugated proteins. Also known as hemoproteins, their structure is formed, in addition to amino acids, by other substances such as metals and ions.
Its three-dimensional shape (distribution in the space of its structure):
Fibrous proteins. Their structure is in the form of long fibers and is insoluble in water.
Globular proteins. Their design is coiled, compact, almost spherical, and usually soluble in water.
What do proteins serve?
Proteins are essential for the human body and its growth. Some of its functions are:
Structural. Many proteins are responsible for giving shape, elasticity, and support to cells and, therefore, to tissues, for example, collagen, elastin, and tubulin.
Immunological. Antibodies are proteins that defend against external agents or infections that affect human and animal bodies.
Motorboat. Myosin and actin are proteins that allow movement. In addition, myosin is part of the contractile ring in cell division, allowing cytokinesis (separation of cells by strangulation).
Enzymatic. Some proteins speed up specific metabolic processes. Some examples of enzyme proteins are pepsin and sucrase.
Homeostatic. Homeostasis is the maintenance of internal balance in organisms. Proteins with a homeostatic function, together with other regulatory systems, maintain the regulation of the pH of these organisms.
Booking. Many proteins are a source of energy and carbon for many organisms. For example, casein and ovalbumin.
Structural levels of proteins
When a protein loses any of its structural levels, it becomes denatured.
The structure of a protein can be classified into various levels of organization and distribution of the units that compose it, according to:
Primary structure. It is the sequence of amino acids that make up a protein (it refers only to the types of amino acids that make up its structure and the order in which they are linked).
Secondary structure. It describes the local orientation of the different segments that make up a protein. Although there are other types, the main ones are Alpha Helix (a part with a spiral structure) and Folded Beta Sheet (a piece with a stretched and folded shape, similar to an accordion). The conditions of both segments are generated and stabilized mainly by hydrogen bonding interactions.
Tertiary structure. It consists of the arrangement in the space of the secondary structure, which can be molded to form globular or fibrous proteins. Tertiary structure is stabilized by Van der Waals interactions, disulfide bonds between sulfur-containing amino acids, hydrophobic forces, and interactions between amino acid radicals.
Quaternary structure. The union of several peptide segments forms it, which is composed of the association of several proteins. Proteins with a quaternary structure are also called oligomeric proteins and do not constitute the majority of proteins. This structure is stabilized by the same interactions that stabilize the tertiary structure.
When proteins are subjected to high temperatures, drastic changes in pH, and some organic solvents’ action, among other factors, they become denatured. Denaturation is the loss of secondary, tertiary, and quaternary structures, which leaves the polypeptide chain without any fixed three-dimensional structure; it could be said it is reduced to its primary system. If tIt denatures if the protein recovers these structures (returns to its original form), the following image represents the different structures of a protein:
Eating a certain amount of protein is the foundation of any healthy diet.
Protein-rich foods are recommended for a healthy, high-protein diet. Shakes provide much of the recommended daily protein source.
There are two types of foods rich in protein, those of plant origin and those of animal origin. High-protein foods of animal origin are eggs, fish, dairy products, and red and white meats. Nuts, soybeans, cereals