There are four most important classes of organic compounds that make up the body: nucleic acids, fats, carbohydrates and proteins. The latter will be discussed in this article.
What is protein?
These are polymeric chemical compounds built from amino acids. Proteins have a complex structure.
How is protein synthesized?
It happens in the cells of the body. There are special organelles that are responsible for this process. These are ribosomes. They consist of two parts: small and large, which are combined during the operation of the organelle. The process of synthesizing a polypeptide chain from amino acids is called translation.
What are amino acids?
Despite the fact that there are a myriad of types of proteins in the body, there are only twenty amino acids from which they can be formed. Such a variety of proteins is achieved due to different combinations and sequences of these amino acids, as well as different placement of the constructed chain in space.
Amino acids contain in their chemical composition two functional groups opposite in their properties:carboxyl and amino groups, as well as a radical: aromatic, aliphatic or heterocyclic. In addition, the radicals may contain additional functional groups. These can be carboxyl groups, amino groups, amide, hydroxyl, guanide groups. The radical may also contain sulfur.
Here is a list of acids from which proteins can be built:
- alanine;
- glycine;
- leucine;
- valine;
- isoleucine;
- threonine;
- serine;
- glutamic acid;
- aspartic acid;
- glutamine;
- asparagine;
- arginine;
- lysine;
- methionine;
- cysteine;
- tyrosine;
- phenylalanine;
- histidine;
- tryptophan;
- proline.
Of these, ten are irreplaceable - those that cannot be synthesized in the human body. These are valine, leucine, isoleucine, threonine, methionine, phenylalanine, tryptophan, histidine, arginine. They must be ingested with food. Many of these amino acids are found in fish, beef, meat, nuts, legumes.
The primary structure of a protein - what is it?
This is the sequence of amino acids in the chain. Knowing the primary structure of a protein, it is possible to draw up its exact chemical formula.
Secondary structure
This is a way to twist the polypeptide chain. There are two variants of protein configuration: alpha helix and beta structure. The secondary structure of a protein is providedhydrogen bonds between CO and NH groups.
Tertiary protein structure
This is the spatial orientation of the spiral or the way it is laid in a certain volume. It is provided by disulfide and peptide chemical bonds.
Depending on the type of tertiary structure, there are fibrillar and globular proteins. The latter are spherical in shape. The structure of fibrillar proteins resembles a thread, which is formed by stacking beta structures or parallel arrangement of several alpha structures.
Quadternary structure
It is characteristic of proteins that contain not one, but several polypeptide chains. Such proteins are called oligomeric. The individual chains that make up their composition are called protomers. The protomers that make up an oligomeric protein can have either the same or different primary, secondary, or tertiary structure.
What is denaturation?
This is the destruction of the quaternary, tertiary, secondary structures of the protein, as a result of which it loses its chemical, physical properties and can no longer fulfill its role in the body. This process can occur as a result of high temperatures acting on the protein (from 38 degrees Celsius, but this figure is individual for each protein) or aggressive substances such as acids and alkalis.
Some proteins are capable of renaturation - the renewal of their original structure.
Protein classification
Given the chemical composition, they are divided into simple and complex.
Simple proteins (proteins) are those that contain only amino acids.
Complex proteins (proteids) - those that have a prosthetic group in their composition.
Depending on the type of prosthetic group, proteins can be divided into:
- lipoproteins (contain lipids);
- nucleoproteins (contains nucleic acids);
- chromoproteins (contain pigments);
- phosphoproteins (have phosphoric acid in their composition);
- metalloproteins (contains metals);
- glycoproteins (contains carbohydrates).
In addition, depending on the type of tertiary structure, there is a globular and fibrillar protein. Both can be simple or complex.
Properties of fibrillar proteins and their role in the body
They can be divided into three groups depending on the secondary structure:
- Alpha structural. These include keratins, myosin, tropomyosin and others.
- Beta structural. For example, fibroin.
- Collagen. It is a protein that has a special secondary structure that is neither an alpha helix nor a beta structure.
Features of fibrillar proteins of all three groups are that they have a filamentous tertiary structure and are also insoluble in water.
Let's talk about the main fibrillar proteins in more detail in order:
- Keratins. This is a whole group of various proteins that are the main component of hair, nails, feathers, wool, horns, hooves, etc. In addition, the fibrillar protein of this group, cytokeratin, is part of the cells, forming the cytoskeleton.
- Myosin. This is a substance that is part of the muscle fibers. Along with actin, this fibrillar protein is contractile and keeps the muscle functioning.
- Tropomyosin. This substance consists of two intertwined alpha helices. It is also part of the muscles.
- Fibroin. This protein is secreted by many insects and arachnids. It is the main component of web and silk.
- Collagen. It is the most abundant fibrillar protein in the human body. It is part of the tendons, cartilage, muscles, blood vessels, skin, etc. This substance provides tissue elasticity. Collagen production in the body declines with age, resulting in skin wrinkles, weakening of tendons and ligaments, etc.
Next, consider the second group of proteins.
Globular proteins: varieties, properties and biological role
The substances of this group have the shape of a ball. They can be soluble in water, solutions of alkalis, s alts and acids.
The most common globular proteins in the body are:
- Albumins: ovalbumin, lactalbumin, etc.
- Globulins: blood proteins (eg hemoglobin, myoglobin), etc.
More on some of them:
- Ovalbumin. This protein is 60 percent egg white.
- Lactalbumin. The main constituent of milk.
- Hemoglobin. It's complexglobular protein, which contains heme as a prosthetic group, is a pigment group containing iron. Hemoglobin is found in red blood cells. It is a protein that is able to bind to oxygen and transport it.
- Myoglobin. It is a protein similar to hemoglobin. It performs the same function - carrying oxygen. Such a protein is found in muscles (striated and cardiac).
Now you know the basic differences between simple and complex, fibrillar and globular proteins.
