Each of us has enough DNA to reach from here to the sun and back, more than 300 times. How is all of that DNA packaged so tightly into chromosomes and squeezed into a tiny nucleus? Histones are a ...

There are four types of base - adenine, thymine, cytosine and guanine. All human cells contain DNA. The 3 billion pairs of bases in each cell fit into a space that is six microns across.