The genetic material packed inside the cells is more solid than liquid | Beta site for NSF

Biochemists have helped answer a fundamental question that has persisted since the discovery of DNA: is chromatin – the complex collection of DNA and proteins in the nucleus of our cells – a solid or a liquid?

In a study funded by the US National Science Foundation published in the journal Cell, a team co-led by Colorado State University biochemist and molecular biologist Jeffrey Hansen, found that chromatin behaves like a solid or gel rather than a liquid. Hansen’s team collaborated with University of Alberta oncologist Michael Hendzel on the study.

Previously, scientists assumed that chromatin and other nuclear elements function in a liquid state. The team’s new knowledge of the physical properties of chromatin challenges this idea and could lead to a more precise understanding of how the genome is encoded and decoded.

The human genome, or the complete set of genetic instructions, is structured into 23 pairs of chromosomes per cell. All of our chromosomes are made from chromatin, which is half structural histone proteins and half DNA. DNA is organized into long chains with bead-like structures called nucleosomes.

Inside the cell nucleus, the chromatin fiber interacts with itself to condense into a chromosome. Chromatin fiber also supports gene expression and chromosomal DNA replication. Although there is some understanding of the structures that make up a nucleus, exactly how these structures are organized and the extent to which the structures interact with each other is not well known.

“Whether a substance is a solid or a liquid is a fundamental property that dictates how that substance works,” Hansen said. “Our genomes are made of condensed chromatin. Discovering that condensed chromatin is a solid will influence all aspects of how we think genomes store and express information, both about health and disease.”

Karen Cone, Program Director of the Division of Molecular and Cellular Biosciences at NSF, added, “This discovery is an important step in understanding how the physical properties of the genome influence its use as an instruction manual for the building blocks of life.”

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