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Physiological basis and concepts of electromyography
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
The thick filaments are formed from proteins known as myosin and the thinner filaments mainly comprise the protein actin. The two proteins, actin and myosin, are essentially responsible for the ability of a muscle to contract. They are therefore also known as contractile proteins. As is shown in Figure 2.9, myosin and actin molecules combine in a characteristic manner to create the filaments. A single myosin molecule is represented schematically in Figure 2.9(a). It comprises thin, elongated parts, the ‘tail’ and the ‘neck’, and a globular ‘head region’. If a number of myosin molecules are introduced into an aqueous solution, they aggregate to form a molecular bundle. During this process the tails of the individual molecules arrange themselves so that they lie parallel to each other. The necks and the heads then protrude out of the sides of the bundle. A very similar arrangement is to be found in the myosin filaments of the muscle. A section of a myosin filament is shown in Figure 2.9(b). The long tails of approximately 200-300 myosin molecules have arranged themselves in parallel to form a bundle. The heads protrude out of the side of the bundle. The diagram indicates the regular arrangement of the heads on the filament. In each case two heads face each other around the circumference of the filament. Each of the ‘pairs of heads’ is set at an angle of approximately 60° in relation to the preceding one. The heads of the myosin filaments form the cross-bridges to the actin filaments referred to in Figure 2.8.
Biochemistry
Published in Ronald Fayer, Lihua Xiao, Cryptosporidium and Cryptosporidiosis, 2007
Structural proteins play critical roles in parasite cell biology and host–pathogen interactions. Similar to other apicomplexans, Cryptosporidium possesses a number of structures unique to the phylum Apicomplexa, including apical complex and oocyst wall. The unique shape of apicomplexan sporozoites and merozoites is maintained by the unique arrangement of cytoskeletal proteins (Morrissette and Sibley, 2002). Actins are one of the major components of the cytoskeleton. Most apicomplexans, including Cryptosporidium, possess only a single conventional actin (with the exception of Plasmodium, which has two) (Gordon and Sibley, 2005). However, Cryptosporidium also possesses seven actin-like proteins (Gordon and Sibley, 2005). Together with myosin, actin plays a critical role in sporozoite gliding motility in C. parvum and other apicomplexans. Recent studies have shown that actin- and myosin-dependent gliding motility is critical to the C. parvum sporozoite invasion. Inhibitors of actin and myosin could inhibit not only gliding motility, but also the invasion of C. parvum sporozoites into host cells (Chen et al., 2004; Sibley, 2004; Wetzel et al., 2005).
Work Capacity, Stress, Fatigue, and Recovery
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
A myofibril is split up into a number of sarcomeres arranged in series (Figure 7.2). A sarcomere consists of many filaments layered over each other in alternating bands. There are two types of filaments. Thick filaments consist of about 300 myosin molecules. Thin filaments consist of a globular protein called actin. The filaments are the true contractile elements of a muscle. Muscles can be likened to bundles of strings all joined together. Each individual string (muscle cell) is made up of fibers (myofibrils) each of which is constructed from many alternating filaments of actin and myosin. The whole structure is bathed in intra- and extracellular fluid and is permeated by blood vessels and nerves.
Energetics of molecular motor proteins: could it pay to take a free ride?
Published in Molecular Physics, 2018
Molecular motor proteins are widely used in biological systems to generate directional motion [1]. They are used to generate actual bodily motion, such as muscle contraction, and in cells to move material from one place to another. Here, we are interested in the latter. Directed transport occurs by motor proteins binding to sites on certain semi-stiff ‘track’ filaments that are assemblies of globular proteins with a polarity. They then process in a given direction, determined by the polarity of the track. The exact mechanism by which this occurs is still a matter of debate. However, the consensus is that the motors hydrolyse ATP and undergo a configurational change that moves them along to the next binding site [2,3]. Motor proteins primarily differ in the track to which they bind and in which direction they move once bound to the track. Myosin binds to actin filaments and provides the driving force for muscle contraction. The motors proteins kinesin and dynein bind to microtubules. Once bound to the track, the former heads towards the positive end of the track and the latter towards the negative end. The end of the protein that does not bind to the track binds to ‘cargoes’, such as proteins and vesicles. Once attached, the motor with loaded cargo transports it along the track. As such, this is the mechanism behind most active transport of proteins and vesicles in the cytoplasm. On the scale of a typical cell, this transport takes place over distances in the order of microns. Directed motion over much longer scales occurs in cells such as axons (a giraffe has an axon [4] that is 2m in length, vying with the giant squid [5] for the record), where it is believed to be linked to various neural dysfunctions including Alzheimer's disease [6].
Proteomic analysis of whole-body responses in medaka (Oryzias latipes) exposed to benzalkonium chloride
Published in Journal of Environmental Science and Health, Part A, 2020
Young Sang Kwon, Jae-Woong Jung, Yeong Jin Kim, Chang-Beom Park, Jong Cheol Shon, Jong-Hwan Kim, June-Woo Park, Sang Gon Kim, Jong-Su Seo
Actin proteins, including four skeletal muscle actins (alpha skeletal muscle, spots 10, 13, 16, and 17) and three cardiac muscle actins (spots 14, 15, and 18), were upregulated by BAC exposure. Actin is a structural protein important for maintaining cellular structure and morphology, and for supporting various cellular functions, including cell division and intra-cellular transport in both muscle and non-muscle cells.[34,35] Chemical and physiological stresses can increase the number of actin-containing stress fibers, thereby arresting cell growth.[36]
Preparation and characterization of gelatin-bioactive glass ceramic scaffolds for bone tissue engineering
Published in Journal of Biomaterials Science, Polymer Edition, 2019
Cell adhesion and proliferation on the scaffold plays a crucial role in bone tissue engineering [50]. Surface characteristics of the biomaterial such as surface roughness, surface area and hydrophilicity are essential factors which determine the cell adhesion and proliferation on the scaffold [52]. Adhesion, proliferation and cell morphology of MG 63 cells was examined using FESEM. Figure 10 shows the FESEM images of the MG 63 cells cultured on pure gelatin and composite scaffold. The micrographs showed that the cells were well attached on the surface of the scaffold. In the case of pure gelatin scaffolds, the cells showed a round morphology and were less spread out on the scaffold surface. In the case of the composite scaffolds, cells were elongated and more spread out. The presence of prominent filopodia was observed which is very crucial for cell proliferation and differentiation. The cells were found to adhere to each other by their filamentous micro-extensions in the case of composite scaffolds. The enhanced cell adhesion and proliferation demonstrated by the composite scaffolds could be because of the increased surface roughness provided by the GC particles. The cytoskeletal organization cell and adhesion of MG 63 cells seeded on gel-GC composite scaffolds were examined by confocal microscopy after staining of nuclei and actin filaments. Figure 10(c) shows the confocal micrograph of Gel-GC composite (GEL BG2) cultured with MG 63 cells. It was observed that the composite scaffold showed good cytoskeletal organization and expression of actin filaments. The expression of actin is very crucial as they mediate cellular movement and structurally support the cells [53]. The obtained results suggested that the composite scaffold supported adhesion and proliferation of osteoblasts.