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Chromosome Condensation
Chromosome condensation refers to the process by which dispersed interphase chromatin is transformed into a set of compact, rod-shaped structures during mitosis and meiosis (Figure 1). The term "chromosome condensation" has long been used in biology. However, it is now increasingly recognized that mitotic chromosome condensation proceeds through mechanisms distinct from those governing "condensation" in physical chemistry (e.g., gas-to-liquid phase transitions) or the formation of "biomolecular condensates" in cell biology. Consequently, some researchers have argued that the term "chromosome condensation" may be misleading in this context. For this reason, alternative terms such as "chromosome assembly" or "chromosome formation" are also commonly used. Processes of chromosome condensation From DNA to chromosomes A diploid human cell contains 46 chromosomes: 22 pairs of autosomes (22 × 2) and one pair of sex chromosomes (XX or XY). The total length of DNA within a single nucleus re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Envelope
The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material. The nuclear envelope consists of two lipid bilayer membranes: an inner nuclear membrane and an outer nuclear membrane. The space between the membranes is called the perinuclear space. It is usually about 10–50 nm wide. The outer nuclear membrane is continuous with the endoplasmic reticulum membrane. The nuclear envelope has many nuclear pores that allow materials to move between the cytosol and the nucleus. Intermediate filament proteins called lamins form a structure called the nuclear lamina on the inner aspect of the inner nuclear membrane and give structural support to the nucleus. Structure The nuclear envelope is made up of two lipid bilayer membranes, an inner nuclear membrane and an outer nuclear membrane. These membranes are connected to each other by nuclear pores. Two sets ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loop Extrusion
Loop extrusion is a major mechanism of Nuclear organization. It is a dynamic process in which structural maintenance of chromosomes (SMC) protein complexes progressively grow loops of DNA or chromatin. In this process, SMC complexes, such as condensin or cohesin, bind to DNA/chromatin, use ATP-driven motor activity to reel in DNA, and as a result, extrude the collected DNA as a loop. Background The organization of DNA presents a remarkable biological challenge: human DNA can reach 2 meters and is packed into the nucleus with the diameter of 5-20 μm. At the same time, the critical cell processes involve complex processes on highly compacted DNA, such as transcription, replication, recombination, DNA repair, and cell division. Loop extrusion is a key mechanism that organizes DNA into loops, enabling its efficient compaction and functional organization. For instance, ''in vitro'' experiments show that cohesin can compact DNA by 80%, while condensin achieves a remarkable 10 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenopus Egg Extract
''Xenopus'' egg extract is a lysate that is prepared by crushing the eggs of the African clawed frog ''Xenopus laevis''. It offers a powerful cell-free (or ''in vitro'') system for studying various cell biological processes, including cell cycle progression, nuclear transport, DNA replication and chromosome segregation. It is also called ''Xenopus'' egg cell-free system or ''Xenopus'' egg cell-free extract. History The first frog egg extract was reported in 1983 by Lohka and Masui. This pioneering work used eggs of the Northern leopard frog ''Rana pipiens'' to prepare an extract. Later, the same procedure was applied to eggs of ''Xenopus laevis'', becoming popular for studying cell cycle progression and cell cycle-dependent cellular events. Extracts derived from eggs of the Japanese common toad '' Bufo japonicus'' or of the Western clawed frog ''Xenopus tropicalis'' have also been reported. Basics of extract preparation The cell cycle of unfertilized eggs of ''X. laevis'' is arres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome Scaffold
In biology, the chromosome scaffold is the backbone that supports the structure of the chromosomes. It is composed of a group of Non-histone protein, non-histone proteins that are essential in the structure and maintenance of eukaryotic chromosomes throughout the cell cycle. These scaffold proteins are responsible for the DNA_condensation, condensation of chromatin during mitosis. Origin In the late 1970s, Ulrich K. Laemmli and colleagues discovered a backbone structure in eukaryotic chromosomes after they depleted the histone proteins. This backbone was localized along the chromosome axis, and was termed the ‘chromosome scaffold’. Proteins of the scaffold In eukaryotic organisms, the DNA of each cell (biology), cell is organized into separated chromosomes, which are composed of chromatin, a mixture of DNA and many different groups of proteins. Among them, the structural proteins (that are not histones) bind the chromatin fiber around themselves forming a long, continuous ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FACT (biology)
FACT (facilitates chromatin transcription, sometimes facilitates chromatin transactions) is a heterodimeric protein complex that affects eukaryotic RNA polymerase II (Pol II) transcription elongation both in vitro and in vivo. It was discovered in 1998 as a factor purified from human cells that was essential for productive, in vitro Pol II transcription on a chromatinized DNA template. FACT consists of 140 and 80 kilodalton (kDa) subunits. The 140 kDa subunit is encoded by the human gene SUPT16H, (SPT16 in '' S. cerevisiae'') while the 80 kDa subunit is encoded by the human gene SSRP1 (POB3 in ''S. cerevisiae''). Both of these subunits in yeast affect Pol II transcription elongation, and purified human FACT binds specifically to mononucleosomes and the histone H2A/ H2B dimer, but not to the H3/ H4 tetramer (see: Nucleosome core particle) or Pol II. Co-immunoprecipitation assays with tagged recombinant proteins showed that the Spt16 subunit interacts with H2A/H2B dimers a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
