Question

Explain why histones from different species are so similar

Short answer

This evolutionary stability indicates that the histones possess critical functions to where the structures are well tuned that they are intolerant to change.

Step-by-step solution

Histones

Histones constitute basic proteins observed in chromosomes. They aid in packing and organization of DNA helix in chromatin fibre in the nucleus. These proteins are rich in arginine and lysine residues.

Explanation of why histones from different species are so similar

Chromatin is about one half protein by mass and 90% of this protein comprises histones. The packaging of DNA can be understood by examining the histone proteins. The major classes of histones include H1, H2A, H2B, H3 and H4, all have a large proportion of positively charged residues. These proteins can therefore bind DNA’s negatively charged phosphate groups.

The amino acid sequence of histones H2A, H2B, H3 and H4 are conserved. For example, histones H4 from cows and peas, exhibit difference by only two conservative residue changes. This makes the protein the most evolutionary proteins. This evolutionary stability indicates that the histones possess critical functions to where the structures are well tuned that they are intolerant to change.