Protein: structure and function.

It is known that proteins - the basis of the origin of life on our planet.According to the theory of Oparin-Haldane was coacervate drops consisting of peptide molecules, it became the basis of origin of living things.This is no doubt because the analysis of the internal structure of any representative of biomass shows that these substances have everything: plants, animals, microorganisms, fungi, viruses.And they are very diverse and macromolecular nature.

name from four of these structures, they are synonymous:

• proteins;
• proteins;
• polypeptides;
• peptides.

Protein molecules

Their number is truly incalculable.In this case all protein molecules can be divided into two major groups:

• simple - composed only of the amino acid sequences joined by peptide bonds;
• complex - structure and structure of a protein characterized by additional protolytic (prosthetic) groups, also called cofactors.

This complex molecules also have their own classification.

graduation complex peptides

1. glycoproteins - are closely related compounds of proteins and carbohydrates.The structure of the molecules are intertwined prosthetic groups mucopolysaccharides.
2. lipoproteins - complex compound of proteins and lipids.
3. metalloproteins - to act as a prosthetic group metal ions (iron, manganese, copper, and others).
4. Nucleoproteins - link proteins and nucleic acids (DNA, RNA).
5. Fosfoproteidy - conformation of the protein and phosphoric acid residue.
6. chromoproteids - very similar to metalloproteins, however, an element that is part of the prosthetic group is a set of colored (red - hemoglobin, green - chlorophyll, and so on).

Each group discussed the structure and properties of proteins are different.The functions that they perform, also vary depending on the type of molecule.

chemical structure of proteins

From this perspective, the proteins - it's a long, solid chain of amino acid residues interconnected specific bonds called peptide.From the side structures acids depart branches - radicals.Such a structure of the molecule was discovered by E. Fischer at the beginning of the XXI century.

more detail later were studied proteins, the structure and function of proteins.It became clear that the amino acids constituting the peptide structure, a total of 20, but they can thus be combined in different ways.Hence, a variety of polypeptide structures.In addition, the process of life and the performance of its functions proteins are able to undergo a series of chemical transformations.As a result, they change the structure of, and there is a completely new type of connection.

To break the peptide bond, ie, break the protein structure of the circuits, it is necessary to choose the very harsh conditions (high temperatures, acids or alkalis, catalyst).This is due to the high strength of the covalent bonds in the molecule, namely in the peptide group.

Detection of protein structure in the laboratory is carried out using biuret reaction - influence on the polypeptide-precipitated hydroxide, copper (II).The complex peptide group and the copper ion gives a bright violet color.

There are four basic structural organization, each of which has its own characteristics of the structure of proteins.

organization levels: the primary structure

As mentioned above, the peptide - a sequence of amino acid residues with inclusions, coenzymes or without them.So this is called the primary structure of the molecule, which is natural, of course, it is the true amino acids joined by peptide bonds, and nothing more.That is, the polypeptide is a linear structure.This particular structure of the proteins of the plan - that is a combination of acids is crucial for the performance of the functions of the protein molecule.Thanks to these features is possible not only to identify the peptide, but also to predict the properties and the role of an entirely new, as yet undiscovered.Examples of peptides having the primary structure of the natural - insulin, pepsin, chymotrypsin, and others.

secondary conformation

Structure and properties of proteins in this category are several changes.Such a structure can be formed initially on the nature or when exposed to harsh initial hydrolysis temperature or other conditions.

This conformation has three varieties:

1. smooth, correct, stereoregular coils constructed from amino acid residues that are twisted around the main axis of the connection.Held together only by hydrogen bonds that occur between oxygen one peptide group and the other hydrogen.Wherein the structure is considered to be due to the fact that the windings are uniformly repeated every 4 unit.Such a structure can be either left-handed or pravozakruchennoy.But in most known proteins dextrorotatory isomer predominates.Such conformation called alpha-structures.
2. composition and structure of proteins following type differs from the previous in that the hydrogen bonds are formed between a number of not standing on one side of the molecule residues, and the considerable distance between, and far enough.For this reason, the whole structure becomes more undulating, snake convoluted polypeptide chains.There is one feature that should be protein.The structure of amino acids on the branches should be as short as that of glycine or alanine, for example.This type of secondary conformation is called beta-sheets for their ability to stick together if the formation of the overall structure.
3. belonging to the third type of structure of the protein biology indicates how complex raznorazbrosannye, disordered fragments that have no stereoregularity and can change the structure under the influence of external conditions.

Examples of proteins having a secondary structure by nature, is not revealed.

Tertiary education

This is a fairly complex conformation that has the name "globule".What is a protein?Its structure is based on secondary structure, however, adding new types of interactions between groups of atoms, and the entire molecule like folds, guided thereby, to ensure that the hydrophilic groups are directed towards the interior of the globule and hydrophobic - outwardly.

This explains the charge of protein molecules in colloidal solutions of water.What types of interactions are there?

1. Hydrogen bonds - remain unchanged between the same parts as in the secondary structure.
2. hydrophobic (hydrophilic) interaction - arise when dissolved in water polypeptide.
3. Ionic attraction - raznozaryazhennymi formed between groups of amino acid residues (radicals).
4. covalent interactions - can be formed between the specific acid sites - cysteine ​​molecules, or rather, their tails.

Thus, the composition and structure of proteins having the tertiary structure can be described as globules rolled into polypeptide chains, holding and stabilizing its conformation due to different types of chemical reactions.Examples of such peptides: fosfoglitseratkenaza, tRNA, alpha-keratin, silk fibroin, and others.

quaternary structure

This is one of the most complex globules that form proteins.Structure and function of proteins, such a plan is very specific and multifaceted.

What is this conformation?This is a multiple (in some cases tens) large and small polypeptide chains, which are formed independently of each other.But then, by the same interactions that we have considered for the tertiary structure, these peptides are twisted and intertwined.Thus obtained complex conformational globules that may contain metal atoms, and lipid groups, and carbohydrate.Examples of such proteins: DNA polymerase, tobacco virus envelope protein, hemoglobin, and others.

All we reviewed the structure of the peptides have their own methods of identification in the laboratory, based on current possibilities of using chromatography, centrifugation, electronic and optical microscopy and high computer technologies.

Functions

structure and function of proteins is closely correlated with each other.That is, each peptide plays a role that is unique and specific.There are those who are able to perform in a living cell, several significant transactions.However, it can in summary form to express the basic functions of protein molecules in the organisms of living beings:

1. propulsion.Celled organisms or organelles, or some type of cell mobility, reductions displaced.This is ensured by proteins that make up the structure of the motor apparatus: cilia, flagella, the cytoplasmic membrane.If we talk about the inability of cells to displacement, the proteins may contribute to their reduction (muscle myosin).
2. nutritional or backup function.It represents the accumulation of protein molecules in egg cells, embryos and plant seeds for future replenishment of the missing nutrients.Upon cleavage of the peptides and amino acids give the biologically active substances that are essential for the normal development of the living organisms.
3. energy function.Apart from carbohydrates forces the body can produce and proteins.In the decay of 1 g of peptide released 17.6 kJ of useful energy in the form of adenosine triphosphate (ATP), which is consumed in the processes of life.
4. warning and regulatory function.It is to implement the close monitoring of ongoing processes and signaling of the cells to tissues from them to the bodies of the latter systems, and so forth.A typical example is insulin, which is strictly fixes the amount of glucose in the blood.
5. receptor function.Carried out by changing the conformation of the peptide with one side of the membrane and engaging the other end of the restructuring.When this occurs the signal transmission and the information required.Most of these proteins are embedded in the cytoplasmic membrane of cells and maintains strict control over all of the material passing through it.Alerting you to the chemical and physical changes in the environment.
6. transport function of the peptides.It is carried out protein channels and carrier proteins.Their role is clear - transport molecules necessary for places with a low concentration of the parts with high.A typical example is the transport of oxygen and carbon dioxide to organs and tissues protein hemoglobin.They also carried out the delivery of compounds with low molecular weight through the cell membrane inside.
7. structure function.One of the most important of those that performs protein.The structure of all cells and their organelles peptides is provided.They are like the frame and shape the structure.Furthermore, they also support and modify it if necessary.Therefore, for the growth and development of all living organisms proteins needed in the diet.Such peptides include elastin, tubulin, collagen, actin, and other keratin.
8. catalytic function.Her performing enzymes.Numerous and varied, they accelerate all chemical and biochemical reactions in the body.Without their participation, ordinary apple in the stomach would be able to digest only for two days, is likely to bend at the same time.Under the action of catalase, peroxidases and other enzymes, this process takes two hours.In general, it is through this role of protein anabolism and catabolism is carried out, that is, the plastic and energy metabolism.

protective role

There are several types of threats, from which proteins are designed to protect the body.

Firstly, chemical attack traumatic reactant gas molecules of substances of different spectrum.Peptides are able to join with them in a chemical reaction, translating into a harmless form or simply neutralizing.

Second, the physical threat of injuries - if the protein fibrinogen time is not transformed into fibrin at the site of injury, the blood does not curdle, and hence blockage will occur.Then, on the contrary, it needs to plasmin peptide capable sucked clot and restore patency of the vessel.

Thirdly, the threat of immunity.The structure and value of the proteins that form the immune defenses, is crucial.Antibodies, immunoglobulins, interferons - are all important and significant elements of the lymphatic and immune system.Any foreign particles, malicious molecule of the dead cells, or the whole structure undergoes immediate study by the peptide compound.That is why a person can own, without the help of drugs every day to protect themselves from infection and simple viruses.

physical properties

cell protein structure is very specific and depends on the function.But the physical properties of peptides are similar and are reduced to the following characteristics.

1. molecular weight - up to 1,000,000 Daltons.
2. in aqueous solution form colloidal systems.There structure acquires charge capable vary depending on the acidity.
3. When exposed to harsh conditions (radiation, acid or alkali, temperature, etc.) can pass to other layers conformations, i.e. denature.This process is 90% irreversible.However, there is a reverse shift - renaturation.

These are the basic properties of the physical characteristics of the peptides.