DNA structure

hello everyone, this DeepInMed blog hope u all doing well. 

DNA is consider as the genetic unit which contain our genetic code found in the nucleas of eukaryotic cells and cytoplasm of prokaryotic cells.

 

it consist of two strands which contain :

sugar (ribose backbone)         nitrgenous base               phosphate group 

nitrogenous bases are nucleotides so what are they? well basically whole DNA is a polymer and every polymer contain monomers these nucleotides are our monomer they consist of pentose sugar, phosphate group and nitrogenous base, there are ribonucleotides and deoxyribonucleotides the only difference between them is the OH group 

and we also have nucleoside which contain nitrogen base and sugar with no phosphate group attached 

nucleotides are divided into to sections : purines and pyrimidines as shown in the figure  and it is good to know that all nucleotides are synthesized as monophosphate and then converted to triphosphate because triphosphate form is the form which DNA and RNA needs. 

DNA methylation : it is known as adding methyl group to cytosine occurs in segments with CG patters in both strands when DNA is methylated its transcription becomes inactivated in fact more than 70% of human genes are methylated as example you and your brother may share the same genes but it is active on you and not on him that doesn't mean he doesn't have your genes since you have the same parents and if the body found a lot of unmethylated CG strands wandering around that can stimulate and immune response because the body will think it came from bacterial DNA methylation and so what is this ? adding methyl group to cytosine and adenine to bacterial DNA but this one have the opposite effect since it protect bacteria from viruses the mechanism is when a viruse insert its DNA into the bacteria the bacteria will recognize that this DNA is not methylated and destroy it by enzyme called endonucleaseas. 

DNA is so large to fit inside the nucleas so it is packaged in chromatin and chromosomes. chromatins are mainly DNA plus proteins and its condensed into chromosomes as shown in the figure. 

   

one of the most important proteins found inside chromatins are the histones and when they combine with DNA they give us nucleosomes as show in the figure down, histones since it is proteins it consist of peptides there names : H1 H2A H2B H3 H4 

and contain amino acids specially ariginine and lysine which are positively charged so the can bind strongly with the negatively charged phosphate backbone 

H1 histone is different from the other histones first it doesn't found in the nucleosome core, larger, important for tying together the beads on the string as shown in the figure it is the big large on and these balls are the other histones in the nucleosome cores 

 a clincal correlation related to histones is drug induced lupus 

as the name stand for it happen after taking certain drugs some symptoms like fever, joint pain and rash these patients will develop anti histone- anti bodies in contrast with patients who have classic lupus (similar symptoms) will develop anti double strand DNA anti bodies. drugs that can stimulate drug induced lupus : procainamide, hydralazine, Isoniazid.

chromatin types : heterochromatin : condensed, gene sequences can't transcribe and the reason is significant DNA methylation. 

euchromain :  less condensed, can perform transcribe perfectly and the reason is significant DNA accetylation. 

DNA accetylation : is adding acetyl group to lysine with will relaxe the chromatin and make more prepare for transcription. and there deacetylase which has just the revert effect and the opposite mechanism. 

huntington's disease is one of the diseases which histone deacetyltion may play a roll, where there is abnormal huntington protien and of the possible mechanism by which this huntington protein becomes over active is by histone deacetylation silence the genes which should control the huntington protein. 

this concludes DNA structure.