the Kernel, ribosomes and fiber synthesis. Nucleinic acids and fiber synthesis

you are: the Kernel, ribosomes and fiber synthesis

DNA exists in the form of two threads, or the chains twirled in a double spiral (fig. 2.10). Each chain represents the linear polymer constructed from nukleotidov of four types. Into structure of everyone nukleotida enter one nitrogenous basis (adenin, guanin, tsitozin or timin), sugar (dezoksi-riboza) and the rest of phosphoric acid. The site of a molecule of DNA, coding full aminokislotnuju sequence of any fiber, is called as a gene. The arrangement order iukleotidov in this or that chain of DNA defines that genetic information which is born by the given molecule (just as letters in any word define its sense). If to designate nukleotidy (on corresponding nitrogenous bases) as A, G, With and T the told will mean that sequences - ACGT - AGCT - and ATCG - contain the different genetic information.

The Information concluded in cellular DNA, carries out in a cage two important functions. First, it provides a continuity of DNA from a cage in a cage as DNA plays a matrix role as well at own reproduction. Secondly, this information is used for synthesis of specific cellular fibers with the assistance of intermediate products - of different types of ribonucleic acids (RNK). RNK differs from DNA that sugar entering into its structure (riboza) contains on one atom of oxygen more than dezoksiriboza DNA. However it at first sight insignificant distinction leads to rather essential distinctions in a configuration and geometry of molecules of these two nucleinic acids.

The Twisting of two spiral chains of DNA in a double spiral is reached as a result of formation between steams of the bases of hydrogen communications (weak communications belonging to number). Adenin and timin approach, for example, because two atoms of hydrogen ostsillirujut between atoms of nitrogen and oxygen of groups of two next rings in molecules adenina and timina (fig. 2.10, an insert).

It is possible to tell, hence, that pairing of the bases And and T, i.e. Formation of pair A-T, is naturally defined by the structure of these molecules. In the same way (this time at the expense of three hydrogen communications) form specific pair G-С guanin and tsitozin. From this specificity follows that if in a matrix chain any information again synthesised chain constructed on this matrix, inevitably should contain komplementarnuju the information is coded. If then this new chain is in turn used as a matrix the chain synthesised on it will represent a copy of an initial matrix.

As a part of a double spiral two chains of a molecule of DNA are closely twirled one round another and consequently are incapable to participate in synthesis but if the spiral is untwisted ability to synthesis is realised, and be shown it can differently. In the presence of enzyme of DNA-polimerazy and a mix of four dezoksiribonukleotidov (in the form rich with energy, namely in the form of corresponding trifosfatov) the new chain of DNA, komplementarnaja is synthesised by the existing. At other stage of a cellular cycle in the presence of RnK-polimerazy and mixes of four ribonukleotidov (also in shape trifosfatov) on the same DNA-matrix instead of DNA it is synthesised RNK. Unique distinction consists in coding of the bases that at synthesis RNK in an under construction chain instead of timina, present at DNA, joins uratsil (U). Thus, hydrogen communications A-T, characteristic for DNA, are replaced in RNK with communications А-U; communications G-С are present at molecules of both these nucleinic acids.

On DNA-matrix three kinds RNK are synthesised. Ribosomnaja RNK (rrnk) enters together with fiber into structure of ribosomes - cellular organell, consisting of two halves different in size having the form spljusnutyh of spheres, pressed one to another. Ribosomes are attached to matrix (information) RNK (mrnk) by the smaller subedinitsej; the group of such ribosomes attached to a thread mrnk, forms a polyribosome (or to a polycatfish) which represents not that other, as the device of albuminous synthesis ready to action. The correct arrangement of amino acids in a molecule of synthesised fiber is provided with that each of 20 amino acids joins at first a molecule the person specific to given amino acid, transport RNK (trnk). Available in a key site of this molecule trnk the sequence from three nukleotidov ' learns ' (by formation of hydrogen communications) komplementarnyj to it nukleotidnyj a triplet in the chain connected with ribosomes mrnk and is attached to a chain in this point. Thus, loaded with amino acids trnk deliver these amino acids to growing linear sequence of the amino acids connected with each other (i.e. To again synthesised fiber) in absolutely certain order. Delivering amino acid to a place, specific trnk separates from it and again it appears ready for the next cycle of carrying over of amino acid. In a certain point of a chain mrnk is available ' a stoplight '-nukleotidnyj a triplet breaking synthesis and causing branch of ready fiber from a ribosome. Each of units of this ensemble (a ribosome, trnk, mrnk) can participate in such cycle many times successively though all of them, certainly, finally are doomed to disintegration and, means, periodically should be updated.