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.

<== попередня сторінка	\|	наступна сторінка ==>
Mononucleotides	\|	Structure of RNA

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