Chromatin

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Chromatin ( DAPI staining, blue) in a mouse cell nucleus. Photographed on the left with a confocal microscope , on the right with the improved resolution of a 3D SIM microscope . In addition, nuclear pores (anti-NPC, red) and the lamina under the nuclear envelope are shown (anti- lamin B, green). In the detailed enlargements at the bottom right it can be seen that there is a chromatin-free space under each of the nuclear pores. The scale corresponds to 5 µm (above) and 1 µm (below).
Parent
chromosome
Subordinate
Euchromatin
Heterochromatin
cytoplasm./nucl. Chromatin
active / resting chromatin
Gene Ontology
QuickGO

Chromatin is the material that chromosomes are made of. It is a complex of DNA and special proteins , about half of which are histones . The name comes from the Greek chroma (color), because chromatin can be colored with basic nuclear dyes. In the light microscope it appears as a visible thread structure in the nucleus of a eukaryotic cell . In a functional sense, everything that is found in the chromosomes during the division of the cell nucleus ( mitosis or meiosis ) is considered chromatin - with the exception of some structural proteins . In addition to the nucleoli , the basic substance of the nucleus and the nuclear envelope, chromatin is an important structural component of the cell nucleus.

Chromatin consists of the DNA that is wrapped around the histones and other proteins that attach to the DNA. DNA and histones form the nucleosomes , which are strung together in a chain. The nucleosomes are packed more tightly with the help of the non-histone proteins. Chromatin is therefore the product of interactions between eukaryotic DNA and different DNA binding proteins that form a compact filamentous complex, the so-called deoxyribonucleoprotein complex, also known as chromatin fibers . As a result of the complex formation, the long chromosomal DNA strands are shortened (condensed) in length by around 10,000 to 50,000 times, so that they fit into the cell nucleus. Despite the dense packing of the DNA, the chromosomes are still in a form that allows regulatory proteins access to the DNA, so that the biosynthesis of RNA and proteins from the genetic information ( gene expression ) or the duplication of the chromosomal DNA ( replication ) is possible .

During mitosis and meiosis, the chromosomes condense so that they can be seen under the light microscope. The smallest chromatin structures visible with a light microscope are called chromonema .

Understanding the structure of chromatin and its contribution to the regulation of genes is part of epigenetics .

Chromatin structures make rods more sensitive in nocturnal mammals because they influence the propagation of light. The phenomenon has not yet been investigated in non-mammals (as of 2010).

Chromatin types

There are two types of chromatin:

  • Euchromatin whose DNA is active, d. i.e. , can be expressed into proteins . The euchromatic sections of the chromosome show no differences in their structure, regardless of the degree of condensation of a chromosome.
  • Heterochromatin , which is mainly composed of inactive DNA. It appears to have structural functions in the various stages of condensation. The heterochromatic sections of the chromosome show the same degree of condensation in the interphase as in the metaphase , i.e. This means that it also remains condensed in the interphase nucleus and appears in the form of dense chromo centers . Heterochromatin can be divided into two subtypes:
    • Constitutive heterochromatin that is never expressed. It is found in the area of ​​the centromere and usually consists of repetitive (repetitive) DNA sequences.
    • Facultative heterochromatin that is sometimes expressed.

Another conceptual demarcation can thus also be made according to the core division phases: Here, the interphase chromatin is loosened up compared to the metaphase chromatin with its very compact chromosomes.

In contrast to eukaryotes, prokaryotes have a circular DNA structure. The eukaryotes have chromosomes that make up the structure of DNA.

Timeline of important discoveries

Timeline of research into chromatin


See also

literature

Evolution:

  • R. Ammar, D. Torti et al. a .: Chromatin is an ancient innovation conserved between Archaea and Eukarya. In: eLife. 1, 2012, pp. E00078 – e00078, doi: 10.7554 / eLife.00078 .

Histone modifications:

  • VG Allfrey: Structural modifications of histones and their possible role in the regulation of ribonucleic acid synthesis . In: Proceedings. Canadian Cancer Conference . tape 6 , 1966, pp. 313-335 , PMID 5934780 .
  • BG Pogo, AO Pogo, VG Allfrey, AE Mirsky: Changing patterns of histone acetylation and RNA synthesis in regeneration of the liver. In: Proceedings of the National Academy of Sciences of the United States of America . tape 59 , no. 4 , 1968, p. 1337-1344 , PMC 224872 (free full text).

Nucleosomes:

  • AL Olins, DE Olins: Spheroid chromatin units (v bodies) . In: Science . tape 183 , no. 4122 , 1974, pp. 330-332 , PMID 4128918 .

Solenoid model:

Individual evidence

  1. ↑ Hans Kleinig and Peter Sitte: Cell Biology. A textbook. 3rd edition, p. 176, Gustav Fischer Verlag (1992).
  2. ^ The Chromatin Database: Chromatin and chromosome structure (accessed June 12, 2009).
  3. ↑ schattenblick.de: Night vision - when every light quantum counts . April 17, 2009.
  4. ^ LA-CP Martins: Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis? In: Genetics and Molecular Biology . tape 22 , no. 2 , June 1999, ISSN  1415-4757 , pp. 261–272 , doi : 10.1590 / S1415-47571999000200022 ( scielo.br [accessed July 22, 2019]).
  5. ↑ Haoyang Lu, Xinzhou Liu, Yulin Deng, Hong Qing: DNA methylation, a hand behind neurodegenerative diseases . In: Frontiers in Aging Neuroscience . tape 5 , 2013, ISSN  1663-4365 , doi : 10.3389 / fnagi.2013.00085 , PMID 24367332 , PMC 3851782 (free full text).
  6. ^ The Francis Crick Papers: The Discovery of the Double Helix, 1951-1953. Retrieved July 22, 2019 .
  7. ^ Ute Deichmann: Epigenetics: The origins and evolution of a fashionable topic . In: Developmental Biology . tape 416 , no. 1 , August 2016, p. 249-254 , doi : 10.1016 / j.ydbio.2016.06.005 ( elsevier.com [accessed July 22, 2019]).
  8. ↑ T. Cremer, M. Cremer: Chromosome Territories . In: Cold Spring Harbor Perspectives in Biology . tape 2 , no. 3 , March 1, 2010, ISSN  1943-0264 , p. a003889 – a003889 , doi : 10.1101 / cshperspect.a003889 , PMID 20300217 , PMC 2829961 (free full text).
  9. ↑ DS Gilmour, JT Lis: Detecting protein-DNA interactions in vivo: distribution of RNA polymerase on specific bacterial genes. In: Proceedings of the National Academy of Sciences . tape 81 , no. 14 , July 1, 1984, ISSN  0027-8424 , p. 4275-4279 , doi : 10.1073 / pnas.81.14.4275 , PMID 6379641 , PMC 345570 (free full text).
  10. ↑ J. Dekker: Capturing Chromosome Conformation . In: Science . tape 295 , no. 5558 , February 15, 2002, p. 1306–1311 , doi : 10.1126 / science.1067799 ( sciencemag.org [accessed July 22, 2019]).
  11. ↑ Marieke Simonis, Petra Klous, Erik Splinter, Yuri Moshkin, Rob Willemsen: Nuclear organization of active and inactive chromatin domains uncovered by chromosome conformation capture-on-chip (Figure 4C) . In: Nature Genetics . tape 38 , no. November 11 , 2006, ISSN  1061-4036 , p. 1348–1354 , doi : 10.1038 / ng1896 ( nature.com [accessed July 22, 2019]).
  12. ↑ J. Dostie, TA Richmond, RA Arnaout, RR Selzer, WL Lee: Chromosome Conformation Capture Carbon Copy (5C): A massively parallel solution for mapping interactions between genomic elements . In: Genome Research . tape 16 , no. 10 , October 1, 2006, ISSN  1088-9051 , p. 1299–1309 , doi : 10.1101 / gr.5571506 , PMID 16954542 , PMC 1581439 (free full text).
  13. ↑ Istvan Albert, Travis N. Mavrich, Lynn P. Tomsho, Ji Qi, Sara J. Zanton: Translational and rotational settings of H2A.Z nucleosomes across the Saccharomyces cerevisiae genome . In: Nature . tape 446 , no. 7135 , March 2007, ISSN  0028-0836 , p. 572-576 , doi : 10.1038 / nature05632 .
  14. ^ E. Lieberman-Aiden, NL van Berkum, L. Williams, M. Imakaev, T. Ragoczy: Comprehensive Mapping of Long-Range Interactions Reveals Folding Principles of the Human Genome . In: Science . tape 326 , no. 5950 , October 9, 2009, ISSN  0036-8075 , p. 289–293 , doi : 10.1126 / science.1181369 , PMID 19815776 , PMC 2858594 (free full text).
  15. ↑ Melissa J. Fullwood, Mei Hui Liu, You Fu Pan, Jun Liu, Han Xu: An estrogen-receptor-α-bound human chromatin interactome . In: Nature . tape 462 , no. 7269 , November 2009, ISSN  0028-0836 , p. 58–64 , doi : 10.1038 / nature08497 , PMID 19890323 , PMC 2774924 (free full text).
  16. ↑ Jesse R. Dixon, Siddarth Selvaraj, Feng Yue, Audrey Kim, Yan Li: Topological domains in mammalian genomes identified by analysis of chromatin interactions . In: Nature . tape 485 , no. 7398 , May 2012, ISSN  0028-0836 , p. 376-380 , doi : 10.1038 / nature11082 , PMID 22495300 , PMC 3356448 (free full text).
  17. ^ Elphège P. Nora, Bryan R. Lajoie, Edda G. Schulz, Luca Giorgetti, Ikuhiro Okamoto: Spatial partitioning of the regulatory landscape of the X-inactivation center . In: Nature . tape 485 , no. 7398 , May 2012, ISSN  0028-0836 , p. 381–385 , doi : 10.1038 / nature11049 , PMID 22495304 , PMC 3555144 (free full text).

Web links

Wiktionary: Chromatin  - explanations of meanings, word origins, synonyms, translations