We all have 6 feet of DNA crammed into the nucleus of every cell. This is somewhere between 5 and 10 billion miles of the stuff in every one of us. So how does all that DNA fit into the average person?
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Due to extremely constricted form.
It is kind of bundled up or cramped. Even the nerves in one human, when laid end to end stretch as long as four times the distance between the earth and the moon.
The protein "histone" is the one responsible for this.
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Each cell has the length of DNA you state but it is wound round histone proteins in what is called a nucleosome. These nucleosomes are packed together in higher order structures, which achieves greater compaction of the DNA. The expression of genes is dependent on the unwinding of these structures, allowing a further control of gene expression. So most of the DNA is packed away but some is accessible in most cells.