There are four of the 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 polymer chemical compounds built from amino acids. Proteins have a complex structure.
How is protein synthesized?
This occurs 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 the 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 various 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 of opposite properties: a carboxyl and an amino group, as well as a radical: aromatic, aliphatic or heterocyclic. In addition, the composition of radicals may include additional functional groups. These can be carboxyl groups, amino groups, amide, hydroxyl, guanide groups. Also, the radical may 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 indispensable - those that cannot be synthesized in the human body. These are valine, leucine, isoleucine, threonine, methionine, phenylalanine, tryptophan, histidine, arginine. They must enter the human body with food. Many of these amino acids are found in fish, beef, meat, nuts, and legumes.
Primary protein structure - what is it?
This is the sequence of amino acids in a chain. Knowing the primary structure of the protein, it is possible to make up its exact chemical formula.
Secondary structure
This is a way to twist a polypeptide chain. There are two protein configuration options: alpha helix and beta structure. The secondary structure of the protein is provided by hydrogen bonds between the 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, fibrillar and globular proteins exist. The latter have a spherical shape. The structure of fibrillar proteins resembles a thread, which is formed by multilayer stacking of beta structures or the parallel arrangement of several alpha structures.
Quaternary structure
It is characteristic of proteins that have in their composition not one, but several polypeptide chains. Such proteins are called oligomeric. Individual chains included in their composition are called protomers. The protomers of which the oligomeric protein is built may have 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 the action of high temperatures on the protein (from 38 degrees Celsius, but for each protein this figure is individual) or aggressive substances such as acids and alkalis.
Some proteins are capable of renaturation - the resumption of its 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) are 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 (there are nucleic acids in the composition);
- chromoproteins (contain pigments);
- phosphoproteins (composed of phosphoric acid);
- metalloproteins (contain metals);
- glycoproteins (there are carbohydrates in the composition).
In addition, depending on the type of tertiary structure, there is a globular and fibrillar protein. Both can be both simple and 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. This is a protein that has a special secondary structure, which is neither an alpha helix nor a beta structure.
The features of fibrillar proteins of all three groups are that they have a threadlike 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 diverse 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 muscle fibers. Along with actin, this fibrillar protein is contractile and provides muscle function.
- Tropomyosin. This substance consists of two interlaced 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 the web and silk.
- Collagen. This is the most common fibrillar protein in the human body. It is part of tendons, cartilage, muscles, blood vessels, skin, etc. This substance provides tissue elasticity. Collagen production in the body decreases with age, which causes wrinkles on the skin, tendons and ligaments weaken, etc.
Next, consider the second group of proteins.
Globular proteins: varieties, properties and biological role
Substances of this group have the shape of a ball. They can be soluble in water, solutions of alkalis, salts and acids.
The most common globular proteins in the body are:
- Albumin: ovalbumin, lactalbumin, etc.
- Globulins: blood proteins (e.g. hemoglobin, myoglobin), etc.
More about some of them:
- Ovalbumin. 60 percent of this protein is egg white.
- Lactalbumin The main component of milk.
- Hemoglobin. This is a complex globular protein, in which heme is present as a prosthetic group - it is a pigment group containing iron. Hemoglobin is found in red blood cells. This is a protein that is able to bind to oxygen and transport it.
- Myoglobin. This is a hemoglobin-like protein. It performs the same function - oxygen transfer. Such a protein is found in the muscles (striated and cardiac).
Now you know the basic differences between simple and complex, fibrillar and globular proteins.