Globular and fibrillar protein: basic characteristics

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 of amino acids. Proteins have a complex structure.

How is the protein synthesized?

This happens in the cells of the body. There are special organoids that are responsible for this process. These are ribosomes. They consist of two parts: small and large, which are combined during the work of the organelle. The process of synthesizing a polypeptide chain of amino acids is called translation.

What are the amino acids?

Despite the fact that the variety of proteins in the body of a myriad of amino acids, from which they can be formed, there are only twenty. Such a variety of proteins is achieved due to various combinations and sequence of these amino acids, as well as different placement of the constructed chain in space.

Amino acids contain in their chemical composition two opposing functional groups: carboxyl and amino, and also the radical: aromatic, aliphatic or heterocyclic. In addition, radicals may include additional functional groups. These can be carboxyl groups, amino groups, amide, hydroxyl, guanide groups. Also, the radical can contain sulfur in its composition.

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 can not be synthesized in the human body. These are valine, leucine, isoleucine, threonine, methionine, phenylalanine, tryptophan, histidine, arginine. They must necessarily enter the human body with food. Many such amino acids are found in fish, beef, meat, nuts, beans.

The primary structure of the protein - what is it?

This is the sequence of amino acids in the chain. Knowing the primary structure of the protein, you can make up its exact chemical formula.

Secondary structure

This is the method of twisting the polypeptide chain. There are two variants of protein configuration: alpha helix and beta structure. The secondary structure of the protein is provided by hydrogen bonds between the CO and NH groups.

Tertiary structure of the protein

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 have a spherical shape. The structure of fibrillar proteins resembles a filament that 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 not one but several polypeptide chains in their composition. Such proteins are called oligomeric. The individual chains that make up their composition are called protomers. The protomers from which the oligomeric protein is constructed can have either the same or different primary, secondary or tertiary structure.

What is denaturation?

This is the destruction of the quaternary, tertiary, secondary protein structures, 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 renewal of their original structure.

Classification of proteins

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 (they have phosphoric acid in the composition);
• Metalloproteins (contain metals);
• Glycoproteins (in the composition there are 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 keratin, 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 consist in the fact that they have a threadlike tertiary structure, and are also insoluble in water.

Let's talk about the basic fibrillar proteins in more detail in order:

• Keratin. This is a whole group of various proteins, which are the main component of hair, nails, feathers, wool, horns, hoofs, etc. In addition, the fibrillar protein of this group of cytokeratin is part of the cells, forming a cytoskeleton.
• Myosin. It is a substance that is a part of muscle fibers. Along with actin, this fibrillar protein is contractile and ensures the functioning of the muscle.
• Tropomyosin. This substance consists of two interlaced alpha-helices. It is also a part of the muscles.
• Fibroin. This protein is isolated 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 a part of tendons, cartilage, muscles, vessels, skin, etc. This substance provides elasticity of tissues. The production of collagen in the body decreases with age, in connection with which wrinkles appear 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 form of a sphere. They can be soluble in water, solutions of alkalis, salts and acids.

The most common globular proteins in the body are:

• Albumins: ovalbumin, lactalbumin, etc.
• Globulins: blood proteins (eg, hemoglobin, myoglobin), etc.

More details about some of them:

• Ovalbumin. Of this protein, egg white is 60 percent.
• Lactalbumin. The main component of milk.
• Hemoglobin. It is a complex globular protein, in which the composition of the prosthetic group is heme - 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's a protein that looks like hemoglobin. It performs the same function - the transfer of oxygen. Such protein is contained in the muscles (striated and cardiac).

Now you know the main differences between simple and complex, fibrillar and globular proteins.