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The concentration and specific composition of histones used can determine local chromatin structure. For example, euchromatin is a form of chromatin with low nucleosome concentration - here, the DNA is exposed, promoting interactions with gene expression, replication, and organizational machinery.
The precise structure of the chromatin fiber in the cell is not known in detail. [10] This level of chromatin structure is thought to be the form of heterochromatin, which contains mostly transcriptionally silent genes. Electron microscopy studies have demonstrated that the 30 nm fiber is highly dynamic such that it unfolds into a 10 nm fiber ...
The solenoid structure can increase this to be 40 times smaller. [2] When DNA is compacted into the solenoid structure can still be transcriptionally active in certain areas. [7] It is the secondary chromatin structure that is important for this transcriptional repression as in vivo active genes are assembled in large tertiary chromatin ...
A chain of nucleosomes can be arranged in a 30 nm fiber, a compacted structure with a packing ratio of ~50 [18] and whose formation is dependent on the presence of the H1 histone. A crystal structure of a tetranucleosome has been presented and used to build up a proposed structure of the 30 nm fiber as a two-start helix. [34]
The basic units of chromatin structure. Histone-modifying enzymes are enzymes involved in the modification of histone substrates after protein translation and affect cellular processes including gene expression. [1] [2] To safely store the eukaryotic genome, DNA is wrapped around four core histone proteins (H3, H4, H2A, H2B), which then join to ...
CTCF binds together strands of DNA, thus forming chromatin loops, and anchors DNA to cellular structures like the nuclear lamina. [10] It also defines the boundaries between active and heterochromatic DNA. Since the 3D structure of DNA influences the regulation of genes, CTCF's activity influences the expression of genes.
Commonly, many people think the structure of a chromosome is in an "X" shape. But this is only present when the cell divides. Researchers have now been able to model the structure of chromosomes when they are active. This is extremely important because the way that DNA folds up in chromosome structures is linked to the way DNA is used.
Bottom: Two tomato SCs with the chromatin removed, allowing kinetochores ("ball-like" structures) at centromeres to be revealed. The synaptonemal complex ( SC ) is a protein structure that forms between homologous chromosomes (two pairs of sister chromatids ) during meiosis and is thought to mediate synapsis and recombination during prophase I ...