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Histones are proteins which organize DNA. The histones themselves are formed the same way all other proteins are formed: they're translated by ribosomes from an mRNA template. How are the clusters formed? They associate with each other and with the DNA. There are five different kinds of histone - 2 copies of four histones ball up to form an octamer, an eight protein ball around which DNA wraps. This is called a nucleosome. The fifth type of histone - called H1 - associates with the DNA stretched between different nucleosomes. If you need more details, let me know.
this gr8 thank you :)....but if the DNA wraps around it then these nucleosomes are positively charged?????
That is a very astute point. :D The areas of the histones which interact with the DNA backbone are predominantly positively charged. The areas which interact with each other have different charges on opposite surfaces for complementary binding.
got it :)....but why are proteins especially used for the packing if DNA inside the nucleus cavity and not hormones or enzymes ??????
Hormones serve other functions. They're really small proteins for starters (the complexes needed to wrap DNA would have to have many more than eight subunits) and they have such potent functions and effects on other molecules that it would be quite dangerous to have so many of them in the cell. As for enzymes, they are a different type of protein with a very specific function: they catalyze reactions. They're not well adapted for 'packaging' and storing DNA. Histones are very tightly regulated proteins: modification of the histone is a big way in which processes involving DNA like transcription and replication are actually regulated. Each histone has a special "tail" region which sticks outward away from the bound DNA and is modified with methyl groups (for example) or phosphorylated. Those modified histones then serve as binding sites for other proteins - transcription factors or repressors - which determine whether or not the DNA is transcribed or replicated.
i forgot that enzymes are a type of proteins :)......thanks alot...you really helped me ...thanks again :D:D
Sure, keep asking!
do plasmids only exist in prokaryotic cells???
okay ...so what is used in the human genetic engineering ???
I don't think we have genetically engineered humans yet.
hehehe..yeah i know that ...i was just wondering if there were experiments carried out or not.....
Maybe in China. Not in the U.S.
well thank you again for ur help :):)