The Science of Existence (120) DNA Folding


Chromatin structure stabilizes and compacts the genome to package it within the nucleus. This structure also serves as a dynamic regulator of gene expression, silencing or activating transcription depending on molecular signals impinging upon it. ~ American biochemist David Sweatt

DNA is always intricately folded: physically shortened by a factor of 10,000 or more to fit inside cells. In human chromosomes, the packing ratio can reach 10 million to 1. This is achieved via 10,000 nonoverlapping loops. Each cell distinctly packs its DNA to suit itself, following some ineffable schema.

The variability is truly astounding. In each being unique, chromosomes are like snowflakes. ~ American geneticist Brian Beliveau

A human cell has 1.8 meters of DNA, wound via histones to 90 micrometers (0.09 mm) of chromatin, which is the combined package of proteins and DNA that comprise genetic information, stored in the nucleus of a eukaryotic cell.

In packaging DNA in compact form, chromatin prevents damage as well as providing a ready means to regulate expression and DNA replication. Altering the efficiency of chromatin affects the employment of the genetic information contained within.

A chromatin has 120 µm of chromosomes after being freshly duplicated and condensed during mitosis. Thousands of proteins are involved in compacting DNA.

DNA is stored in a fractal Matryoshka pattern: nested self-similar globules of sequences, highly organized spatially, and systematically nested. The spatial architecture of chromosomes and other genetic structures is critical to their operation. This crucial aspect of genetics is barely understood.

In defiance of the topological complexity that characterizes folded DNA, identical sequences can recognize each other from a distance and even gather together. When bound in double-helix form, nucleobases are tucked away, hidden behind their nucleotide support structures of charged sugar and phosphate groups. A likely explanation for such sequence identification goes to conformity in shape and charge pattern, but this is an incomplete reckoning. The inherent intelligence involved in such recognition by these DNA strands remains a mystery.