How Chromosomes Pack Without Exploding
When preparing to divide, a cell has to copy all its DNA accurately and pack it into chromosomes. A professor at U Chicago told Science Daily this is “like compacting your entire wardrobe into a shoebox.” The cell has another difficulty in this compaction process, though: DNA, being negatively charged, resists packing.
Eukaryotes overcome the resistance by neutralizing the negative charge with histones. DNA wraps around the histones, forming nucleosomes, which then coil and supercoil into the familiar chromosomes. One class of marine algae, the dinoflagellates, uses a different method: it neutralizes the negatively-charged DNA with positively-charged ions of calcium and magnesium.
The U Chicago team was puzzled at this exception to the rule. They wondered if “this may have been the first and very efficient step toward the goal of neutralizing DNA, long before histones came into play.” The statement was only a suggestion, however. It also does not explain why dinoflagellates have much more nuclear DNA than human beings.
One observation, though, was dynamic. When the scientists removed the positively-charged ions from the dinoflagellate DNA, the chromosomes exploded.
Did they find a sequence from positive-ion neutralization to histone neutralization? No; their evolutionary belief dictates that they use imagination and speculation to invent stories to link different organisms with common ancestry. There are puzzles to solve here, for sure. Why would a marine alga have so much more DNA than a human? Why would it use a different method of neutralizing the DNA? Don’t let these puzzles overshadow the major question: how genetic information arose that could be systematically and accurately copied, then condensed by orders of magnitude into a tiny space. If you ever figure out how to compact your wardrobe into a shoebox, one thing is certain: you will not have done it by an evolutionary process.