Proteins are organic substances.These high-molecular compounds are characterized by a specific composition and decompose upon hydrolysis into amino acids.Protein molecules can be of various forms, many of which consist of several polypeptide chains.Information about the structure of the protein encoded in the DNA, and the process of synthesis of protein molecules called translation.
chemical composition of proteins
The average protein contains:
- 52% carbon;
- 7% hydrogen;
- 12% nitrogen;
- 21% oxygen;
- 3% sulfur.
protein molecule - a polymer.In order to understand the structure, you need to know what constitutes their monomers - amino acids.
Amino
They can be divided into two categories: constantly occurring and is sometimes found.The former include the monomers 18 protein and two amide: aspartic acid and glutamic acid.Sometimes there are only three acids.
These acids can be classified in different ways: by the nature of the side chains, or charge them radicals, as they can be divided by the number of groups CN and COOH.
primary structure of the protein
order of alternation of amino acids in the protein chain determines its subsequent levels of the organization, properties and functions.The main form of communication between the monomers is a peptide.It is formed by hydrogen abstraction from one aminoksloty and OH group of the other.
The first level of organization of the protein molecules - is the amino acid sequence it is simply a chain which determines the structure of protein molecules.It consists of a "skeleton" having a regular structure.This repetitive sequence -NH-CH-CO-.Certain side chains of amino acids are presented radicals (R), their properties determine the composition of protein structure.
Even if the structure of protein molecules the same, they differ only on properties that have different sequences of monomers in the chain.The order of the amino acids in the protein of the genes and protein dictates certain biological functions.The sequence of monomer molecules which are responsible for the same function often close in different species.Such molecules - the same or similar in organization and carrying out of various species of organisms same function - homologous proteins.The structure, properties and functions of future molecules already laid at step chain amino acid synthesis.
some similarities
structure of the protein has been studied for a long time, and the analysis of the primary structure will make some generalizations.For a greater number of proteins characterized by the presence of all twenty amino acids, many of which are particularly glycine, alanine, aspartic acid, glutamine and little tryptophan, arginine, methionine, histidine.Exceptions are only a few groups of proteins, such as histones.They are needed to pack DNA and contain a lot of histidine.
second generalization: in globular proteins are no general laws in the alternation of amino acids.But even in distant biological activity of the polypeptides are small fragments of identical molecules.
secondary structure
second level of organization of the polypeptide chain - is its spatial location, which is maintained by hydrogen bonds.There are α-helix and β-pleated.Part of the chain does not have an ordered structure, such zones are called amorphous.
alpha helices of natural proteins pravozakruchennaya.Side groups of amino acids in helix always facing outwards and located on opposite sides of its axis.If they are non-polar, is their grouping on one side of the spiral arc obtained, which create the conditions for convergence of different helical regions.
Beta-fold - greatly elongated spiral - tend to stay in the protein molecule and a number of parallel and non-parallel form a β-pleated layers.
tertiary structure of the protein
third level of organization of the protein molecule - folding spirals, folds and amorphous areas in a compact structure.This occurs due to the interaction between the side chains of the monomers themselves.Such links are divided into several types:
- hydrogen bonds formed between the polar radicals;
- hydrophobic - between non-polar R-groups;
- electrostatic attractive forces (ionic bonds) - between the groups, a charge which is opposite;
- disulfide bridges - between cysteine radicals.
latter type of connection (-S = S-) is a covalent interaction.Disulfide bridges strengthen proteins, their structure becomes stronger.But the presence of such links does not necessarily.For example, cysteine may be very small in the polypeptide chain, or it radicals situated next and can create a "bridge".
fourth level of organization
quaternary structure of form, not all proteins.The structure of the protein on the fourth level determined by the number of polypeptide chains (protomers).They are interconnected by the same constraints as the previous level of organization but disulfide bridges.The molecule consists of a number of protomers, each has its special (or identical) tertiary structure.
all levels of the organization determine the functions that will carry the resulting proteins.The structure of the proteins at the first level of organization very precisely determines their subsequent role in the cell and the organism as a whole.
protein function
hard to imagine how important is the role of proteins in the cell activity.We have considered their structure.The functions of proteins depend directly on it.
executed construction (structural) function, they form the basis of any of the cytoplasm of a living cell.These polymers are the main material of all cellular membranes when comprised in a complex with a lipid.This includes cell division into compartments, each with its own flow reaction.The fact that for each complex cellular processes needed the conditions, particularly pH plays an important role environment.Protein build thin walls that divide the cell in the so-called compartments.But the phenomenon has been called compartmentalization.
catalytic function is to regulate all the reactions of the cell.All enzymes origin are simple or complex proteins.
Any kind of movement of organisms (working muscles, the movement of protoplasm in a cell, blinking cilia in the simplest, and so on. D.) Is carried out proteins.The structure of proteins allows them to move to form fibers and koltsa.Transportnaya function is that many substances are transported across the cell membrane specific carrier proteins.
Hormone role of these polymers is clear at once: on the structure of a number of hormones are proteins, such as insulin, oxytocin.
Spare function is defined by the fact that proteins can form deposits.For example, valgumin eggs, casein milk proteins of plant seeds - they kept a large amount of nutrients.
All tendons, articular joints, bones, hooves formed proteins, which brings us to another of their functions - supporting.
receptors are protein molecules, carrying out selective recognition of certain substances.In such a role is particularly known glycoproteins and lectins.
most important factors of immunity - antibodies and complement system are the proteins in origin.For example, the process of blood coagulation based on changes in the protein fibrinogen.The inner walls of the esophagus and stomach are lined with a protective layer of mucous proteins - Licinius.Toxins are also proteins in origin.The basis of the skin, protecting the animal's body is collagen.All these functions are protective proteins.
Well, the last function of the account - regulatory.There are proteins that control the operation of the genome.That is, they regulate transcription and translation.
Whatever are playing an important role proteins, protein structure was unriddled scientists for a long time.And now they are opening new ways to use that knowledge.
