A famous philosopher once said: "Life is a form of existence of protein bodies." And he was absolutely right, because it is this organic substance that is the basis of most organisms. Quaternary structure protein has the most complex structure and unique properties. Our article will be devoted to him. We will also consider the structure of protein molecules.
What is organic matter
A large group of organic substances is united by one common property. They are made up of several chemical elements. They are called organic. These are hydrogen, oxygen, carbon and nitrogen. They form organic substances.
Another common feature is that they are all biopolymers. These are large macromolecules. They are made up of a large number of repeating units called monomers. For carbohydrates, these are monosaccharides, for lipids, glycerol and fatty acids. But DNA and RNA are made up of nucleotides.
Chemicalstructure of proteins
Protein monomers are amino acids, each of which has its own chemical structure. This monomer is based on a carbon atom, it forms four bonds. The first of them - with a hydrogen atom. And the second and third, respectively, are formed with an amino and carbox group. They determine not only the structure of biopolymer molecules, but also their properties. The last group in an amino acid molecule is called a radical. This is exactly the group of atoms in which all monomers differ from each other, which causes a huge variety of proteins and living beings.
Structure of a protein molecule
One of the characteristics of these organic substances is that they can exist at different levels of organization. This is the primary, secondary, tertiary, quaternary structure of the protein. Each of them has certain properties and qualities.
Primary structure
This protein structure is the simplest in structure. It is a chain of amino acids linked by peptide bonds. They are formed between the amino and carboxy groups of neighboring molecules.
Secondary structure
When a chain of amino acids coils into a helix, the secondary structure of a protein is formed. The bond in such a molecule is called hydrogen, and its atoms form the same elements in the functional groups of amino acids. Compared to peptides, they have much less strength, but are able to hold this structure.
Tertiary structure
But the next structure is a ball into which a spiral of amino acids is twisted. It is also called a globule. It exists due to the bonds that arise between the residues of only a certain amino acid - cysteine. They are called disulfides. This structure is also supported by hydrophobic and electrostatic bonds. The former are the result of attraction between amino acids in the aquatic environment. Under such conditions, their hydrophobic residues practically "stick together", forming a globule. In addition, amino acid radicals have opposite charges that attract each other. This results in additional electrostatic bonds.
Protein of quaternary structure
The quaternary structure of a protein is the most complex. This is the result of the merger of several globules. They can differ both in chemical composition and in spatial organization. If a protein of a quaternary structure is formed only from amino acid residues, it is simple. Such biopolymers are also called proteins. But if non-protein components are attached to these molecules, proteins appear. Most often, this is a combination of amino acids with carbohydrates, nucleic and phosphoric acid residues, lipids, individual iron and copper atoms. In nature, complexes of proteins with natural coloring substances - pigments are also known. This structure of protein molecules is more complex.
The spatial form of the quaternary structure of a protein isdefining its properties. Scientists have found that filamentous or fibrillar biopolymers do not dissolve in water. They perform essential functions for living organisms. Thus, the muscle proteins actin and myosin provide movement, and keratin is the basis of human and animal hair. Spherical or globular proteins of the quaternary structure are highly soluble in water. Their role in nature is different. Such substances are able to transport gases like blood hemoglobin, break down food like pepsin, or perform a protective function like antibodies.
Protein properties
A quaternary protein, especially a globular one, can change its structure. This process occurs under the influence of various factors. These are most commonly high temperatures, concentrated acids, or heavy metals.
If a protein molecule unwinds to a chain of amino acids, this property is called denaturation. This process is reversible. This structure is able to form globules of molecules again. This reverse process is called renaturation. If the amino acid molecules move away from each other and peptide bonds are broken, degradation occurs. This process is irreversible. Such a protein cannot be restored. Destruction was carried out by each of us when we fried eggs.
Thus, the quaternary structure of a protein is the type of bond that is formed in a given molecule. It is strong enough, but under the influence of certain factors it can collapse.
