Before a cell divides, its DNA condenses a thousandfold so that each chromosome is clumped together. Now a report in Cell <23 July 1999> offers an explacountry of exactly how a cell accomplishes this design triumph. The results carry out a possible solution to the problem of how the DNA in each humale cell (which, if stretched end-to-finish, would certainly meacertain around a metre) not only fits into the tiny cell nucleus yet, when vital, scrunches up still more.

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DNA in a cell is a bit like a coiled telephone cord. Sometimes telephone cords acquire all tangled up in a bunch so that one portion of the cord is crossing over another bit. When this happens to DNA it is dubbed supercoiling. If the coil happens to overlap itself in one direction, it is referred to as a ?positive supercoil?; if in the opposite direction, a ?negative supercoil?.

During the majority of of the life of a cell, its DNA is spcheck out out in the nucleus. This enables the cellular machinery access to it in order to analyze it right into proteins. But when a cell is around to divide it makes a copy of its whole DNA, and also then the chromosomes condense and line up in a row.

The initially part of this bunching is assisted along by a mass of proteins dubbed histones, around which the DNA wraps favor string approximately a yo-yo. But when it is wrapped around the hirock the DNA is still about ten times as long as it needs to be. This is wright here the brand-new research comes in. Nicholas Cozzarelli of the University of The golden state, Berkeley, and also colleagues show that this protein dubbed 13S condensin can make DNA twist up right into positive supercoils.

Researchers recognize that this protein somejust how completes the job, but, till now, no one had actually any kind of concept how. Unlike a phone cord, which, a lot to one?s irritation, sometimes appears to desire to coil up spontaneously, winding up DNA in the very same way takes a lot of power. Cozzarelli?s group confirmed that 13S condensin gets its power from ATP - the energy-generator of the cell (although they caution that the experiments were done in a test tube, not a cell). They additionally showed that condensin deserve to carry out its point just when the cell is gaining prepared to divide. At various other times throughout the cell?s life, it doesn?t have this feature.

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Wunsch, H. How DNA does the twist. (1999).

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Published: 05 August 1999




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