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General Introductory Topics
Published in Vadim Backman, Adam Wax, Hao F. Zhang, A Laboratory Manual in Biophotonics, 2018
Vadim Backman, Adam Wax, Hao F. Zhang
It used to be believed that heterochromatin is transcriptionally silent, while euchromatin is where transcription occurs. Understanding chromatin structure and function is currently a frontier science, and it is becoming increasingly clear how complex the functional anatomy of chromatin really is. Recent studies have shown that what was once a clear-cut distinction between heterochromatin and euchromatin in terms of their transcriptional activity is no longer unquestionable. For example, studies have demonstrated that transcription does occur in heterochromatin.
Enzyme Kinetics and Drugs as Enzyme Inhibitors
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
About 2 m of DNA are present in each nucleated cell, packed as chromatin, a macromolecular complex of DNA and histone proteins. Chromatin is present in an open form (euchromatin) containing most of the transcriptionally active genes, and in a more compact, transcriptionally silent, state. A transition from one state to the other is mediated by chemical modification of the chromatin proteins. The study of these phenomena, the biology of chromatin, is what is termed epigenetics (see also Wong and Yu; Volume 6 of this Series).
Chaos in Space
Published in Pier Luigi Gentili, Untangling Complex Systems, 2018
The relevant role that a fractal structure may have on the chemical kinetics is also proved in the nucleus of a eukaryotic cell. In the nucleus, the chromatin is a long polymer (each human cell contains about two meters of DNA) that fills the available volume with a compact polymorphic structure on which the transcription, replication, recombination, and repair of the genome occur. The three-dimensional architecture of chromatin is crucial to the functioning of a cell. Chromatin is a hierarchical structure spanning four spatial scales: from few nanometers to tens of micrometers. In fact, it is constituted by DNA (≈2 nm tick); nucleosomes (i.e., segments of DNA, each one wrapping eight histone proteins and forming a complex ≈10 nm long); chromatins that are fibers ≈30 nm high, generated by the nucleosomes that fold up; higher order chromatin loops and coils ≈300 nm in length, and, finally, ≈1.4 μm chromosome territories contained in the nucleus ≈20 μm large. Chromatin is actually a fractal (Bancaud et al. 2012). Some areas of the nucleus contain heterochromatin made of DNA packed tightly around histones. Other nuclear areas contain euchromatin that is DNA loosely packed. Usually, genes in euchromatin are active, whereas those in heterochromatin are inactive. The different activity is related to the different fractal structure (Bancaud et al. 2009). In fact, euchromatin seems to have a higher fractal dimension (d ≈ 2.6), exposing a broader and rougher surface to the proteins scanning for their target sequences. Heterochromatin has a smaller fractal dimension (d ≈ 2.2) because it is flatter and smoother and has a less extended surface. The more accessible DNA surfaces in euchromatin can be scanned more efficiently by nuclear factors favoring active transcription than in the heterochromatin. These conclusions have been drawn by collecting the time evolution of luminescent signals emitted by fluorescent proteins and markers (Bancaud et al. 2009). The decays of light-emitted intensities (I(t)) coming from fractal structures can be fitted by the stretched exponential (or Kohlrausch or KWW) function: [] I(t)=I0e−(tτ)β
Development of an improved lentiviral based vector system for the stable expression of monoclonal antibody in CHO cells
Published in Preparative Biochemistry and Biotechnology, 2019
Omid Mohammadian, Masoumeh Rajabibazl, Es’hagh Pourmaleki, Hadi Bayat, Roshanak Ahani, Azam Rahimpour
In order to overcome the negative effects of neighboring chromatin, including heterochromatin formation and the surrounding cis-acting elements, the use of regulatory DNA elements such as nuclear scaffold/matrix attachment regions (SAR/MAR) in both viral and non-viral expression vectors has been extensively employed by researchers. SARs are specific DNA sequences in the eukaryotic chromatin which attach to the nuclear matrix and facilitate the formation and maintenance of euchromatin.[20] Previous studies have demonstrated that SARs can shield introduced foreign genes from chromosome position effects.[21,22]
The effects of a high-fat diet on the liver of pregnant albino rats and their developing offspring
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Abdelalim A. Gadallah, Abdullah R. Almasari
At ultrastructural level, the hepatocytes had a nucleus with a thin peripheral heterochromatin and inner core of euchromatin material. The cytoplasm contained abundant rough endoplasmic reticulum and mitochondria with differentiated inner cristae (Figure 5).