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Physics Colloquium

Nucleoid Physics

Presented by Associate Professor Jaan Mannik

The code of life in all living organisms on Earth is DNA. The DNA molecule is a polymer chain comprising A, T, G, C nucleobase monomers. The chain is typically about 1000 times longer than a characteristic dimension of a cell that hosts this molecule. How a DNA molecule is compacted in a cell determines how its encoded information is retrieved and duplicated.

A nuclear membrane encloses DNA molecules in our cells, but no nuclear membrane is present in bacteria. Nevertheless, DNA in a bacterial cell is compacted to a distinct cellular region termed the nucleoid, which occupies about half of the cell volume. Several processes have been proposed to contribute to DNA compaction, including looping and cross-linking DNA by proteins, twisting DNA to supercoils by molecular motors, transient DNA attachments to the cell membrane, and osmotic compression by macromolecular crowders. We have studied the role of macromolecular crowders in compacting the Escherichia coli nucleoid in live cells. Altogether, our results support the idea that a diverse array of cytosolic proteins and stable RNA molecules are the main factors compacting the bacterial DNA to a distinct cellular entity that phase-separates from the rest of the cell. Equilibrium statistical physics appears thus to offer a sufficient framework to explain one of the main organizational principles in a bacterial cell.

Monday, September 20, 2021 at 3:30pm

Science and Engineering Building, 307
1414 Circle Drive, Knoxville, TN 37996

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