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Cross-bridge theory states that actin and myosin form a protein complex (classically called actomyosin) by attachment of myosin head on the actin filament, thereby forming a sort of cross-bridge between the two filaments. The sliding filament theory is a widely accepted explanation of the mechanism that underlies muscle contraction.
Chromatin bridges may form by any number of processes wherein chromosomes remain topologically entangled during mitosis. One way in which this may occur is the failure to resolve joint molecules formed during homologous recombination mediated DNA repair, a process that ensures that replicated chromosomes are intact before chromosomes are segregated during cell division.
Cytological markers of BFB-cycle-mediated chromosomal instability: "budding" nuclei (A, C, D) and partly fragmented nucleus with double nucleoplasmic bridge (B). [1] Breakage-fusion-bridge (BFB) cycle (also breakage-rejoining-bridge cycle) is a mechanism of chromosomal instability, discovered by Barbara McClintock in the late 1930s. [2] [3]
The structure that results is a cross-strand exchange, also known as a Holliday junction. The contact between two chromatids that will soon undergo crossing-over is known as a chiasma . The Holliday junction is a tetrahedral structure which can be 'pulled' by other recombinases, moving it along the four-stranded structure.
During the first months of the COVID-19 pandemic, such a recombination event was suggested to have been a critical step in the evolution of SARS-CoV-2's ability to infect humans. [32] Linkage disequilibrium analysis confirmed that RNA recombination with the 11083G > T mutation also contributed to the increase of mutations among the viral progeny.
For example, in the context of protein function, the binding of calcium to troponin in muscle cells can induce a conformational change in troponin. This allows for tropomyosin to expose the actin-myosin binding site to which the myosin head binds to form a cross-bridge and induce a muscle contraction. [21]
Donald Trump mocked Canadian Prime Minister Justin Trudeau after his top minister’s surprise resignation following a clash on how to handle the president-elect’s looming tariffs.
This process aligns actin and myosin filaments for efficient cross-bridge formation while also recruiting myosin heads from dormant states into contraction-ready configurations. [ 6 ] [ 10 ] Additionally, stretching the sarcomeres sensitizes the thin (actin) filaments to calcium, promoting stronger and more sustained contractions. [ 6 ]