DNA and chromosomes may seem like completely separate things. Well, they’re not. In fact, all chromosomes are individual DNA molecules coiled and twisted around, because DNA is huge. At least in eukaryotes it is. That’s one of the first differences between eukaryotes and prokaryotes in their DNA – prokaryotes have less DNA.
Eukaryotic DNA is stored within the nucleus of each cell (apart from cells without one, e.g. red blood cells). Because of its sheer size, it must be organised well. Proteins called histones help do just that:
In eukaryotes, mitochondria and chloroplasts have their own DNA. Similarly to prokaryotes, this organelle DNA is short, circular and not associated with proteins.
Having already covered the basics of DNA, let’s turn our attention to the principles which govern what actually happens to DNA and how this results in life being…