A macromolecule is a molecule that has a high molecular weight. Its structure is presented in the form of repeatedly repeating links. Consider the features of such compounds, their significance for the life of living beings.
Features of the composition
Biological macromolecules are formed from hundreds of thousands of small starting materials. Living organisms are characterized by three main types of macromolecules: proteins, polysaccharides, nucleic acids.
The initial monomers for them are monosaccharides, nucleotides, amino acids. A macromolecule is almost 90 percent of the cell mass. Depending on the sequence of amino acid residues, a specific protein molecule is formed.
High molecular weight are those substances that have a molar mass greater than 103 Da.
History of the term
When did the macromolecule appear? This concept was introduced by Nobel Laureate in Chemistry Hermann Staudinger in 1922.
The polymer ball can be seen as a tangled thread that was formed by accidental unwindingthroughout the coil room. This coil systematically changes its conformation; this is the spatial configuration of the macromolecule. It is similar to the trajectory of Brownian motion.
The formation of such a coil occurs due to the fact that at a certain distance the polymer chain "loses" information about the direction. It is possible to talk about a coil in the case when high-molecular compounds are much longer in length than the length of the structural fragment.
Globular configuration
A macromolecule is a dense conformation in which one can compare the volume fraction of a polymer with a unit. The globular state is realized in those cases when, under the mutual action of individual polymer units between themselves and the external environment, mutual attraction occurs.
A replica of the structure of a macromolecule is that part of the water that is embedded as an element of such a structure. It is the closest hydration environment of the macromolecule.
Characterization of a protein molecule
Protein macromolecules are hydrophilic substances. When a dry protein is dissolved in water, it initially swells, then a gradual transition into solution is observed. During swelling, water molecules penetrate into the protein, binding its structure with polar groups. This loosens the dense packing of the polypeptide chain. A swollen protein molecule is considered a back solution. With the subsequent absorption of water molecules, the separation of protein molecules from the total mass is observed, andthere is also a process of dissolution.
But the swelling of a protein molecule does not in all cases cause dissolution. For example, collagen after absorption of water molecules remains in a swollen state.
Hydrate theory
High-molecular compounds according to this theory do not just adsorb, there is an electrostatic binding of water molecules with polar fragments of side radicals of amino acids that have a negative charge, as well as basic amino acids that carry a positive charge.
Partially hydrated water is bound by peptide groups that form hydrogen bonds with water molecules.
For example, polypeptides that have non-polar side groups swell. When binding to peptide groups, it pushes the polypeptide chains apart. The presence of interchain bridges does not allow protein molecules to completely break away, go into the form of a solution.
The structure of macromolecules is destroyed when heated, resulting in a break and release of polypeptide chains.
Features of gelatin
The chemical composition of gelatin is similar to collagen, it forms a viscous liquid with water. Among the characteristic properties of gelatin is its ability to gel.
These types of molecules are used as hemostatic and plasma-substituting agents. The ability of gelatin to form gels is used in the production of capsules in the pharmaceutical industry.
Solubility Featuremacromolecules
These types of molecules have different solubility in water. It is determined by the amino acid composition. In the presence of polar amino acids in the structure, the ability to dissolve in water increases significantly.
Also, this property is affected by the peculiarity of the organization of the macromolecule. Globular proteins have a higher solubility than fibrillar macromolecules. In the course of numerous experiments, the dependence of dissolution on the characteristics of the solvent used was established.
The primary structure of each protein molecule is different, which gives the protein individual properties. The presence of cross-links between polypeptide chains reduces solubility.
The primary structure of protein molecules is formed due to peptide (amide) bonds; when it is destroyed, protein denaturation occurs.
S alting out
To increase the solubility of protein molecules, solutions of neutral s alts are used. For example, in a similar way it is possible to carry out selective precipitation of proteins, to carry out their fractionation. The resulting number of molecules depends on the initial composition of the mixture.
The peculiarity of proteins, which are obtained by s alting out, is the preservation of biological characteristics after complete removal of s alt.
The essence of the process is the removal by anions and cations of the s alt of the hydrated protein shell, which ensures the stability of the macromolecule. The maximum number of protein molecules is s alted out when sulfates are used. This method is used to purify and separate protein macromolecules, since they are essentiallydiffer in the magnitude of the charge, the parameters of the hydration shell. Each protein has its own s alting out zone, that is, for it you need to select s alt of a given concentration.
Amino acids
Currently, about two hundred amino acids are known that are part of protein molecules. Depending on the structure, they are divided into two groups:
- proteinogenic, which are part of macromolecules;
- non-proteinogenic, not actively involved in the formation of proteins.
Scientists have managed to decipher the sequence of amino acids in many protein molecules of animal and plant origin. Among the amino acids that are quite often found in the composition of protein molecules, we note serine, glycine, leucine, alanine. Each natural biopolymer has its own amino acid composition. For example, protamines contain about 85 percent arginine, but they do not contain acidic, cyclic amino acids. Fibroin is a protein molecule of natural silk, which contains about half of the glycine. Collagen contains such rare amino acids as hydroxyproline, hydroxylysine, which are absent in other protein macromolecules.
Amino acid composition is determined not only by the characteristics of amino acids, but also by the functions and purpose of protein macromolecules. Their sequence is determined by the genetic code.
Levels of structural organization of biopolymers
There are four levels: primary, secondary, tertiary, and also quaternary. Each structurethere are distinctive characteristics.
The primary structure of protein molecules is a linear polypeptide chain of amino acid residues linked by peptide bonds.
It is this structure that is the most stable, since it contains peptide covalent bonds between the carboxyl group of one amino acid and the amino group of another molecule.
The secondary structure involves the stacking of the polypeptide chain using hydrogen bonds in a helical form.
The tertiary type of biopolymer is obtained by the spatial packing of the polypeptide. They subdivide spiral and layered-folded forms of tertiary structures.
Globular proteins have an elliptical shape, while fibrillar molecules have an elongated shape.
If a macromolecule contains only one polypeptide chain, the protein has only a tertiary structure. For example, it is a muscle tissue protein (myoglobin) necessary for oxygen binding. Some biopolymers are built from several polypeptide chains, each of which has a tertiary structure. In this case, the macromolecule has a quaternary structure, consisting of several globules combined into a large structure. Hemoglobin can be considered the only quaternary protein that contains about 8 percent histidine. It is he who is an active intracellular buffer in erythrocytes, which allows maintaining a stable blood pH value.
Nucleic acids
They are macromolecular compounds that are formed by fragmentsnucleotides. RNA and DNA are found in all living cells; it is they that perform the function of storing, transmitting, and also implementing hereditary information. Nucleotides act as monomers. Each of them contains a residue of a nitrogenous base, a carbohydrate, and also phosphoric acid. Studies have shown that the principle of complementarity (complementarity) is observed in the DNA of different living organisms. Nucleic acids are soluble in water but insoluble in organic solvents. These biopolymers are destroyed by increasing temperature, ultraviolet radiation.
Instead of a conclusion
In addition to various proteins and nucleic acids, carbohydrates are macromolecules. Polysaccharides in their composition have hundreds of monomers, which have a pleasant sweetish taste. Examples of the hierarchical structure of macromolecules include huge molecules of proteins and nucleic acids with complex subunits.
For example, the spatial structure of a globular protein molecule is a consequence of the hierarchical multilevel organization of amino acids. There is a close connection between the individual levels, the elements of a higher level are connected with the lower layers.
All biopolymers perform an important similar function. They are the building material for living cells, responsible for the storage and transmission of hereditary information. Each living being is characterized by specific proteins, so biochemists face a difficult and responsible task, solving which they save living organisms from certain death.
