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Thus, acetylation of histones is known to increase the expression of genes through transcription activation. Deacetylation performed by HDAC molecules has the opposite effect. By deacetylating the histone tails, the DNA becomes more tightly wrapped around the histone cores, making it harder for transcription factors to bind to the DNA.
Condensation of long double-helical DNAs is a sharp phase transition, which takes place within a narrow interval of condensing agent concentrations.[ref] Since the double helices come very closely to each other in the condensed phase, this leads to the restructuring of water molecules, which gives rise to the so-called hydration forces.[ref] To ...
Around 146 base pairs (bp) of DNA wrap around this core particle 1.65 times in a left-handed super-helical turn to give a particle of around 100 Angstroms across. [8] The linker histone H1 binds the nucleosome at the entry and exit sites of the DNA, thus locking the DNA into place [9] and allowing the formation of higher order structure. The ...
The bases become unstacked and can thus absorb more light. In their native state, the bases of DNA absorb light in the 260-nm wavelength region. When the bases become unstacked, the wavelength of maximum absorbance does not change, but the amount absorbed increases by 37%.
The buoyant density of most DNA is 1.7g/cm 3. [11] DNA does not usually exist as a single strand, but instead as a pair of strands that are held tightly together. [9] [12] These two long strands coil around each other, in the shape of a double helix.
Heterochromatin is a tightly packed form of DNA or condensed DNA, which comes in multiple varieties. These varieties lie on a continuum between the two extremes of constitutive heterochromatin and facultative heterochromatin. Both play a role in the expression of genes.
DNA photoionization is the phenomenon according to which ultraviolet radiation absorbed directly by a DNA system (mononucleotide, single or double strand, G-quadruplex…) induces the ejection of electrons, leaving electron holes on the nucleic acid. The loss of an electron gives rise to a radical cation on the DNA.
DNA within the nucleosome remains fully wrapped for only 250 ms before it is unwrapped for 10-50 ms and then rapidly rewrapped, as measured using time-resolved FRET. [40] This implies that DNA does not need to be actively dissociated from the nucleosome but that there is a significant fraction of time during which it is fully accessible.