Primary st. of DNA is a spirally one polynucleotides chain (PNC), the disposition of nucleotides in which determine all hereditary properties of organism.

The lincage between nucleotides 3,5 phosphodiesther.

This polynucleotides chain has free 5-end and 3-end.

The secondary st. of DNA represents two spiral molecules of polynucleotide chains. They are connected among themselves by hydrogen bonds between complementary nitrogenous bases (A – T, G – C). One rotation of this helix contain of 10 nucleotides and is equal 3,4 nanometer (B-form). The bases of both chains are located strict perpendicularly to axes of chain.

The deoxyribose and phosphoric acid is disposed on the axes of helix. The secondary st. of DNA is stabilized not only by bonds between bases, but also by hydrophobic interaction between n. Bases of own chain, which are locates each on other as a roulean of coins. The double helix is stabilized by electrostatic interaction between negativally charged chain of DNA and positive charged of histon’s molecules.

The tertiary st. of DNA is superspiralization – the double spiral (140 nucleotides) is winded up on the octet of from fourth pair of histons – 2H2α, 2H2β, 2H3, 2H4.

On this octet mol. of DNA makes 2 rotation of double spiral.

This place is named nucleosome. It is inactive part of DNA. The part of DNA between 2 nucleosomes is connected with histone, (H1) and is active part of DNA.

The quarternary structure of DNA of man and mammalian animals forms chromosomes. Chromosomes consist of chromatin. It consist from: DNA – 3-5%, histones – 30-50%, nonhistone proteins – 40-50%, their number is about 580 proteins. The biggest part of chromatin is inactive – 90% in cells of brain, 97% in liver, 98% in other tissues. Active part of chromatin makes 2-10% only.

The quarternary str. of DNA leads to very dense packing of DNA in chromosomes, so the DNA by 2 meters is packed into 5 nanometers.

In linear str. of DNA the occurence of pins can be observed. The pins of DNA are named also palyndromes. The information from p. can read equaly from left to right and from right to left as in word mum, pap.

For example, GAA TTC CTT AAG.

So in these sides (places) the genetic information is read out in both direction. The functions of p. is unknown, but they help to regulation protein to find out a place of genetic information. Therefor DNA contains also the sequences which do not contain of genetic information. They are named intrones and sides (places) of gene are named exons. Introns play regulating function.

There are the mobile side’s in DNA – jumping genes. Their migration is explained by the mechanism of reversible transcription, when genetic information read out from RNA on DNA with revertase.

DNA-à RNA-à protein.

This is main postulate of molecular biology. In 1974 Themin and Baltimor opened revertase – enzyme which can read out information in reversible way from RNA to DNA. This processe is called reversible transcription. When mobile gene stays near oncogenes the last is activated and cancer can develope.

Some virus contain of revertase (virus rubella, measec influenza) and that is why they can lead to mutations.

In some microbs 5 and 3 ends of each chain DNA is connected each other by covalent bonds, forming ring.

Except for a large ring of DNA located in a meclea zone there are one or several small rings of DNA, which are located in free condition in cytoplasma. This extranuclear DNA is named Plasmid. Usually the plasmides contain of only few genes.

They are capable independently replicate and during division of cells pass in new cells. The plasmids are allocated from microbe cells very easily. There is special form of DNA in microbe cells – circular DNA. This form is named plasmide and has very small sizes – about 100 of bases pair. The plasmid function is and this property of plasmid is used widely in genetic ingeenering, when a new genes from other organismus – microbes, vegetables, animals are transferred to plasmid and modified plasmids are transferred into new cells and these cells begin to synthize new proteins – insulin, somatotropin.

There are about base pairs (bp) in each human haploid genome. The average gene length is bp and genome could consist of 10 genes. Only 10% of DNA codes for protein. The function of the remaining 90% of the human genome is regulatory but the function of this part probably has not yet been defined.

Structure of RNA

All RNA have unary (sole) individual polynucleotide chain. Their Mm is less than Mm of DNA. The content of RNA in cells is changed depending on age, function, tempreture. Mononucleotides of RNA contain ribose as pentose, A, G as purine bases and U, C as pyrimidine base.

There are 3 kinds of RNA: messenger RNA – mRNA, transfer RNA – tRNA, ribosomal RNA – rRNA.

MRNA is discovered by Jackob and Maneau in 1961. It makes 2-3% from all quantities of cellular RNA. It does not have (has not) rigid specific secondary structure. Its sole polynucleotide chain forms the different loops bands and changs constantly dependly from ionic concentration of solution. In unworking condition mRNA turn into globulla. During the function the polynucl. Chain of RNA is opened and stretched mRNA is synthesized on DNA in nucleus and this process is called transcription. MRNA is carrier of the genetic information from DNA to aminoacid’s sequence of protein. The place of every a/a in proteins is coded by sequence of mononucleotide in mRNA.

The idea of genetic code has arised by known physics Gamov – an author of theory of extending universe. Gamov supposed that cells have the dictionary translating the fourth letter alphabet text in the twenty word’s alphabetic of protein.

In 1961 M. Nirenberg and G. Mattei synthesized m.RNA, consisting from uridil only – polyuridil and synthesized on them protein, consisting of residues of phenylalanine only. The number of the phenylalanine residues was less than number of uridile residues in three times so they established that phenylalanine is coded by three uridiles. This message was made on 5-th biochemical congress in Moscow in 1961 and has caused sensation since at last the biochemists can possible to understand what is gene, from what it consists of. In decoding a genetic code the large role had played the research Crick, Nirenberg, Holly, Corana. Last three scientist have received the Nobel premium in 1968.

Now the genetic code is completely deciphered. Now is proved that the arrangement of aminoacids in polypeptide is defined by three mononucleotides. So the genetic code is triplet. Triplets of mRNA has received the name “codon”.

From four of nucleotide (A, G, C, U) by rules rearrangements it is possible to construct 64 codons of mRNA.

From this number 61 codons ciphers 20 aminoacids. Three codons do not cipher any aminoacids, they play a role of “stop codons” or terminal codons. There are 20 a/a and 61 codons from 20 a/a only tryptophan and methionine have one codon only and other – 2-3-6 codons. This property of a genetic code are named a degeneration. The researches have shown that first two letters codone define the specificity everyone codone and the third letter has smaller significance for specificity.

The following property of a code is its universality. Same a/a is coded by identical codones as an viruses, microbes, in vegetative (plants), as and the animal cells.

At last cod is unremitting. It does not interrupt by any stopping marks. The reading out a code from one point only – is uncrossed cod.

This characteristic is lawful for a cod at a level mRNA only.

The coding of the genetic information in DNA occurs more difficultly and complicatly and this process still is not found out up to the end.

However recently it is established that one sequence of mononucleotides can be ciphered the structure two or even of three proteins. Experiments with DNA of bacteriophage XI74 proved that there are other genes inside gene of bacteriophage. Such phenomenon economizes a genetic material a square of cell, occupied by DNA.

Other rules of code are exposed to doubt also ( triplet, degeneration, uncrossing).

Thus mRNA accepts direct participation in biosynthesis of proteins. Now the questions of synthesis of artificial mRNA are successfully decided. Such mRNA for hemoglobin are synthesized by Corana in USA and Kiselev in Russia.

Ribosomal RNA (rRNA)

The rRNA makes more than 80% of all cellular RNA. RRNA come into the composition of ribosomes. Ribosomes are nucleoprotein complexes, they consist of rRNA (65%) and proteins (35%). Everyone of rRNA joints with 30 protein’s molecules. Every ribosome consist of two subunits – big and small in ratio 2,5:1. Ribosomes make 25% of cell’s mass, 60% of their mass are hydrated and that is why different hydrophylic substances penentrate to them easily.

The polynucleotide chain of rRNA coils and joints with proteins making compact body.

The function of ribosomes is possible when they are intact. One break of polynucleotide chain of mRNA and ribosome lead to lose their biological activity.

When mRNA joints with one ribosome the matrix is formed. When mRNA joints with few ribosomes the polysome is formed.

MRNA plays specific role in matrix and polysome. The role of rRNA is nonspecific and ribosomes of frog can synthesized hemoglobin of rabbit if they joint with mRNA of hemoglobin of rabbit.

tRNA (transport or transfer RNA) contains in cytoplasm and makes approximately 10% of all cellular RNA. tRNA is investigated better than mRNA and rRNA. Their molecules are small, their molecular mass is 20000D and consist of 75±5 nucleotides.

Basic role of tRNA is transport and installation of aminoacids on the corresponding codone of mRNA. Separate tRNA correspond to everyone aminoacid, so tRNA-s are specific to aminoacids, their specificity is provided by enzyme – aminoacylsynthetase. Nowdays not only primary structure (sequence of nucleotides) of tRNA is investigated, but their secondary structure is known.

In 1965 Holly and Baev have established structure for valine tRNA which has appeared universal for all tRNA. A molecule of tRNA in denaturated condition has form of trifolium or a clover-leaf shape. In active condition is curtailed in globulus. There are 4 active centers in tRNA. 1- acceptor stalk – site with a final sequence of nucleotides ACC. This center joints different aminoacids. Kind of jointing of aminoacids depends of nucleotide’s sequence of second center, which is different for different aminoacids. This center is jointed with aminoacylsynthetase, which is specific for each aminoacids and only than aminoacylsynthetase joints determined aminoacids to determined aminoacid to acceptor’s stalk.

Third center in tRNA is site for connection with ribosome. Fourth center is named anticodon which consist of three nucleotides, bases of which gives the tRNA a remarkable property to recognize the codon presenting over the mRNA and coding the aminoacid because bases in anticodon are complementary to bases of codone.

So the role of tRNA is recognize the place of every aminoacid on the mRNA and therefor in the protein’s molecule.

tRNA “markes” of aminoacids giving them the specificity and establishes aminoacid on determined codon in mRNA. The characteristic feature a structure of tRNA is the presence of minor (modified) bases – methyl-, oxy-, thyobases. For example – pseudouracil, dehydrouracil.

These modified bases are capable to unclassical pairing. In this connection the quantity of tRNA is less almost in 2 times than the quantity of codones. For example modified base hypocsantine (purine) can form hydrogen bonds with C, A, G. The second peculiarity of modified bases is the feaility, fragility of hydrogen bonds, which they form. This promotes to easier clearing from a complex codon – anticodon. If all 3 bases of anticodons have formed strong Watson-Creak’s pair the connection between codon – anticodon would be so strong, that releasing of tRNA from a complex with mRNA would occur slowly and limited speed protein’s synthesis.

Enzymes

An enzymes can be defined as a protein produced by living cells, which is capable of catalysing a chemical reaction to yield specific products in other words, an enzyme is a biological catalyst. Their role is very large. So, academic Pavlov was saying: “ The enzymes are the center of biological and medical knowledge “. Braunsthein said: “All modern biochemistry speaks on enzyme’s language”.

The word enzyme means “derived from yeast” and was used when the catalytic properties of the yeast were discovered. A catalyst is an agent which in small amounts increases the velocity of a reaction without appearing in the final products of the reaction.

The substance on which an enzyme acts is called its substrate. The names of enzymes usually end is “ase” which is preceded by the name of its substrate. Many enzymes have been crystallized in pure form (now near 2500): urease was the first enzyme to be crystallized in 1926 by Sumner. The enzymes can bring about chemical reaction in body tissues or even in vitro at comparatively low temperature and low dilutions.