G Grehan | Search PubMed

PubMed1999

The mechanical advantages of DNA.

The elastic properties of DNA and the contractile activities of enzymes involved in transcription, translation and supercoiling may have contributed to the ability of early cells (protocells) to withstand turgor pressure. In the hypothesis proposed here, resistance to turgor resulted from (1) the elastic properties of DNA which was connected to the membrane by association with positively charged lipids and with membrane peptides, (2) the coupled transcription-translation-insertion of peptides into membrane--transertion--which connected membranes with phase-condensed DNA, and (3) the action of topoisomerases which supercoiled and shortened DNA. The existence of a negative feedback system is also proposed to explain how weakened regions of membrane were preferentially strengthened. It may prove possible to test this hypothesis by studying transertion using optical tweezers and by studying wall-less L-form bacteria.

DNA↗

PubMedDate not supplied

Hypothesis: hyperstructures regulate bacterial structure and the cell cycle.

A myriad different constituents or elements (genes, proteins, lipids, ions, small molecules etc.) participate in numerous physico-chemical processes to create bacteria that can adapt to their environments to survive, grow and, via the cell cycle, reproduce. We explore the possibility that it is too difficult to explain cell cycle progression in terms of these elements and that an intermediate level of explanation is needed. This level is that of hyperstructures. A hyperstructure is large, has usually one particular function, and contains many elements. Non-equilibrium, or even dissipative, hyperstructures that, for example, assemble to transport and metabolize nutrients may comprise membrane domains of transporters plus cytoplasmic metabolons plus the genes that encode the hyperstructure's enzymes. The processes involved in the putative formation of hyperstructures include: metabolite-induced changes to protein affinities that result in metabolon formation, lipid-organizing forces that result in lateral and transverse asymmetries, post-translational modifications, equilibration of water structures that may alter distributions of other molecules, transertion, ion currents, emission of electromagnetic radiation and long range mechanical vibrations. Equilibrium hyperstructures may also exist such as topological arrays of DNA in the form of cholesteric liquid crystals. We present here the beginning of a picture of the bacterial cell in which hyperstructures form to maximize efficiency and in which the properties of hyperstructures drive the cell cycle.

Bacteria↗