Biomedical subjects

M Harmouchi

Publications and source records attributed to M Harmouchi.

5 recordsLinked to original sources

PubMed1992

Effect of a mechanical tension on the hydration of DNA in fibres.

Fiber X-ray diffraction and measurement of fibre dimensions yield information about the effects of a mechanical tension on hydration of DNA in fibres. At a given relative humidity, the mechanical tension changes the DNA conformation but does not modify the number of water molecules associated to a nucleotide. The number of water molecules per nucleotide necessary to maintain B form decreases for increasing tensions applied to the DNA fibre. Form transitions can be opposed by mechanical tensions; an energy of 1 Kcal per mole of nucleotide pairs is sufficient to prevent the B to A transition.

DNA↗

PubMed1990

Changes of hydration during conformational transitions of DNA.

Fiber X-ray diffraction and measurement of fiber dimensions yields information about the hydration of DNA in fibers. The results obtained give us the fraction of nucleotides in the B form for the A-B transition or the rate of progression for the B-C transition as functions of the number of water molecules per nucleotide. The present experimental results confirm the importance of cooperativity in the A-B transition and the progressive change of the DNA double helix conformation during the C-B transition. At least twenty additional water molecules per nucleotide are necessary to stabilize the B form for DNA molecules in fibers following the A to B transition whereas only ten are sufficient when the B conformation is obtained starting from the C form.

DNA↗

PubMed1990

A method for the experimental study of DNA conformational transitions in fibers.

The method proposed for the study of DNA conformational transitions is based on the proportionality, experimentally observed, between the length of a DNA fiber and the axial rise per nucleotide characterizing the molecular helix. Precise curves for the A-B and B-C transitions as a function of the relative humidity are obtained by using X-ray fiber data and measurements of fiber dimensions. It is thus shown that the A-B transition is a cooperative process between two different states, whereas the B-C transition can be considered as a progressive change of conformation. The present method is applied on two natural DNAs differing in base composition so that the effect of the nucleotide content on the conformational changes can be estimated.

DNA↗

PubMed1989

[Experimental method for studying conformational transitions in DNA].

An experimental method combining fiber X-ray and direct fiber dimension measurements is proposed for the study of DNA conformational transitions. Curves corresponding to the A-B and B-C transitions are obtained by using the proportionality which exists between the fiber length and the axial rise per nucleotide in the DNA helix. The A-B transition is shown to be cooperative while the B-C one is a progressive change of helical conformation.

DNA, Superhelical↗

PubMed1988

Influence of a mechanical tension on the B-A and B-C conformational transitions in DNA fibres.

In the present fibre X-ray study we attempt to quantify the effect of a mechanical tension on the conformations, and transitions between the structural forms of DNA. A simple experimental device has been realized in order to apply precise mechanical forces on DNA fibres during X-ray exposure. It is shown that, as the applied tension is increased, the B----A transition can be prevented as well as with a decrease of the sodium salt content. A kind of distorted B form is then observed the helical parameters of which change with the relative humidity. On the contrary, the mechanical tension does not prevent the B----C transition; it only slows down the form change and improves the X-ray patterns up to a relative humidity of 0%.

Animals↗