DNA molecule - a polynucleotide monomer units which are the four deoxyribonucleotide (dAMF, dGMP, dCMP and dTMP).The ratio of the sequence of these nucleotides in the DNA of various organisms differ.In addition to the major nitrogenous bases in DNA contains other deoxyribonucleotides with minor bases: 5-methylcytosine, 5-oksimetiltsitozin, 6 methylaminopurin.
Once there was a possibility of using the method of X-ray crystallography to study biological macromolecules and produce perfect radiographs, managed to find out the molecular structure of DNA.This method is based on the fact that the parallel beam of X-rays incident on a crystalline cluster of atoms, forms a diffraction pattern, which mainly depends on the atomic weight of the atoms, and their location in space.In the 40s of the last century it has been put forward the theory of three-dimensional structure of the DNA molecule.U. Astbury proved that the deoxyribonucleic acid is a stack of superposed one on another flat nucleotides.
primary structure of the DNA molecule
Under the primary structure of nucleic acids involve contiguous nucleotides in the polynucleotide chain of DNA.Nucleotides are linked together by phosphodiester bonds which are formed between the OH group in the 5-position of deoxyribose nucleotide and one OH group in position 3 of another pentose.
biological properties of nucleic acids defined quality ratio and the sequence of nucleotides along the polynucleotide chain.
nucleotide composition of DNA in organisms of different taxonomic groups with specific and determined by the ratio (G + C) / (A + T).With specificity rate was determined by the degree of heterogeneity of nucleotide composition of DNA in organisms of various origins.Thus, in higher plants and animals ratio (T + C) / (A + T) varies slightly and has a value greater than 1. For microorganisms coefficient specificity varies widely - from 0.35 to 2.70.However, somatic cells of a species of DNA contain the same nucleotide composition, ie. E. It can be said that the content of GC base pairs in the DNA of one species are identical.
Determination of heterogeneity of nucleotide composition of DNA at a rate of specificity does not give information on its biological properties.This is caused by a different nucleotide sequence specific sites in the polynucleotide chain.This means that the genetic information encoded in DNA molecules in its specific sequence of monomeric units.
DNA molecule comprises a nucleotide sequence destined for the initiation and termination of DNA synthesis (replication) of RNA synthesis (transcription) protein synthesis (translation).There are nucleotide sequences that are specific for binding and activating inhibitory regulatory molecules, as well as nucleotide sequences which do not carry any genetic information.There are also modified the field, which protect the molecules from nucleases.
problem nucleotide sequence of DNA to date is not fully resolved.Determination of nucleotide sequences of nucleic acids is time-consuming procedure involving the application of the method specific nuclease cleavage fragments into separate molecules.Today, the complete nucleotide sequence of the nitrogenous bases installed in most tRNAs of different origin.
molecule of DNA secondary structure
Watson and Crick have designed a model of the double helix of deoxyribonucleic acid.According to this model, the two polynucleotide chains entwine with each other, forming a kind of spiral.
of bases in which are located inside the structure, and the phosphodiester backbone - outside.
molecule of DNA tertiary structure
linear DNA in the cell has the shape of an elongated molecule, it is packed into a compact structure and takes only 1/5 of the volume of the cell.For example, the length of the DNA of human chromosome reaches 8 cm and is packaged so that fits into a chromosome with a length of 5 nm.This is possible thanks to the styling spiralized DNA structures.From this it follows that the double-stranded DNA helix in space can be further installing a specific tertiary structure - supercoil.Supercoiled conformation of the DNA characteristic of the chromosomes of higher organisms.This tertiary structure is stabilized by covalent bonds with the amino acid residues that make up the proteins which form nucleoprotein complex (chromatin).Therefore, the DNA of eukaryotic cells associated with proteins mainly basic character - histones as well as acidic proteins and fosfoproteidami.
