Solenoid structure

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When solenoid structure ( French solenoids of Greek sols , channel 'and Greek eidos , form') of the DNA is the packaging of the DNA as a 30  nm chromatin fiber referred to, which is the result of several condensations nucleosomes is (a so-called. "Coiled coil" structure , a kind of wound coil).

DNA packaging stages

In eukaryotic cells are 146  bp approximately 1.65 times a DNA histone octamer (two histone H2A , a histone 2B - dimer and a histone H3 - histone H4 tetramer) looped. The histone octamer with its DNA coil is called a nucleosome. Histone H1 also tightens the DNA that is bound to the histone octamer. The nucleosomes, which look like pearls on a string (“beads on a string” structure), are further condensed into a helical structure through the interactions of the amino-terminal ends (NH 2 ) of the histone octamers. In this helix there are about six nucleosomes per turn. X-ray crystallography suggests a pitch of about 11 nm. This overall structure is called a solenoid, and is just one of two models used to describe the packaging of the 30 nm filaments of DNA. The other is the so-called zigzag model. Like the solenoid model, this too has been observed using an electron microscope. More recent X-ray crystallographic studies show that both models are presumably correct, since the lengths of the linker DNA differ greatly in studies (the zigzag model is favored by longer connecting DNA).

DNA packaged in solenoids is not transcriptionally active . As solenoids continue to condense, chromosomes become recognizable. Solenoids continue to wind around each other to form a loop of around 20,000 to 80,000 bp, followed by a rosette that contains six connected loops. This is followed by a spiral structure and finally the chromatids. At the end there is the highly compressed metaphase chromosome. The most highly packed chromatin has a diameter of about 600 nm.

Individual evidence

  1. ↑ solenoid . Online Etymology Dictionary
  2. ↑ JR Daban: High concentration of DNA in condensed chromatin. In: Biochem Cell Biol. Vol. 81, No. 3, June 2003, pp. 91-99, doi: 10.1139 / o03-037 .
  3. ^ JO Thomas: The higher order structure of chromatin and histone H1. In: J Cell Sci Suppl. Volume 1, 1984, pp. 1-20, doi: 10.1242 / jcs.1984.Supplement_1.1 .
  4. ^ A b Baker, Bell, Gann, Levine, Losick: Molecular Biology . Ed .: James D. Watson. 6th, updated edition. Pearson Studium, Munich 2011, ISBN 978-3-86894-029-9 , pp. 203-204 .
  5. ^ GS Manning: Packaged DNA. An elastic model. In: Cell Biophys. Volume 7, No. 1, March 1985, pp. 57-89, doi: 10.1007 / BF02788639 .
  6. ↑ David Latchman: Eukaryotic Transcription Factors Fourth Edition. Elsevier, London 2004, pp. 2-3, ISBN 978-0-08-053126-7 .