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Cell fusion is an important cellular process in which several uninucleate cells (cells with a single nucleus) combine to form a multinucleate cell, known as a syncytium.Cell fusion occurs during differentiation of myoblasts, osteoclasts and trophoblasts, during embryogenesis, and morphogenesis. [1]
[11] [verification needed] [12] [13] This has led many texts to delineate between membrane-bounded and non-membrane bounded organelles. [14] The non-membrane bounded organelles, also called large biomolecular complexes , are large assemblies of macromolecules that carry out particular and specialized functions, but they lack membrane boundaries.
A dimer composed of SMC5 and SMC6 functions as part of a yet-to-be-named complex implicated in DNA repair and checkpoint responses. [10] Each complex contains a distinct set of non-SMC regulatory subunits. Some organisms have variants of SMC proteins. For instance, mammals have a meiosis-specific variant of SMC1, known as SMC1β. [11]
The location of NORs and the nucleolar cycle in human cells. Nucleolus organizer regions (NORs) are chromosomal regions crucial for the formation of the nucleolus.In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. [1]
Examples are the class of nuclear receptors located in the cell nucleus and cytoplasm and the IP 3 receptor located on the endoplasmic reticulum.The ligands that bind to them are usually intracellular second messengers like inositol trisphosphate (IP 3) and extracellular lipophilic hormones like steroid hormones.
The tertiary structures and biological functions of many nucleoproteins are understood. [ 2 ] [ 3 ] Important techniques for determining the structures of nucleoproteins include X-ray diffraction , nuclear magnetic resonance and cryo-electron microscopy .
Homology shared by members of the Mcm2-7 protein family. [5] Homology among the six members of the family are indicated in black. Homology of each member across species is indicated in colour. The minichromosome maintenance proteins were named after a yeast genetics screen for mutants defective in the regulation of DNA replication initiation. [6]
Intermediate filaments are composed of a family of related proteins sharing common structural and sequence features. Initially designated 'intermediate' because their average diameter (10 nm ) is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells, the diameter of intermediate filaments is now ...