What is cytoplasm made off?
5184#0
In cell biology, the cytoplasm is all of the material within a cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The main components of the cytoplasm are cytosol – a gel-like substance, the organelles – the cell's internal sub-structures, and various cytoplasmic inclusions. The cytoplasm is about 80% water and usually colorless.
Cytoplasm
656613#15
"Neurospora crassa" is a multicellular fungus with many off shooting hyphae. Cells can be up to 10 cm long, and are separated by a small septum. Small holes in the septum allow cytoplasm and cytoplasmic contents to flow from cell to cell. Osmotic pressure gradients occur through the length of the cell to drive this cytoplasmic flow. Flows contribute to growth and the formation of cellular subcompartments.
Cytoplasmic streaming
656613#6
What is clearly visible in plants cells which exhibit cytoplasmic streaming is the motion of the chloroplasts moving with the cytoplasmic flow. This motion results from fluid being entrained by moving motor molecules of the plant cell. Myosin filaments connect cell organelles to actin filaments. These actin filaments are generally attached to the chloroplasts and/or membranes of plant cells. As the myosin molecules "walk" along the actin filaments dragging the organelles with them, the cytoplasmic fluid becomes entrained and is pushed/pulled along. Cytoplasmic flow rates can range between 1 and 100 micron/sec.
Cytoplasmic streaming
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Cytoplasmic flows created through osmotic pressure gradients flow longitudinally along the fungal hyphae and crash into the end causing growth. It has been demonstrated that the greater pressure at the hyphal tip corresponds to faster growth rates. Longer hyphae have greater pressure differences along their length allowing for faster cytoplasmic flow rates and larger pressures at the hyphal tip. This is why longer hyphae grow faster than shorter ones. Tip growth increases as cytoplasmic flow rate increases over a 24 hour period until a max rate of 1 micron/second growth rate is observed. Off shoots from the main hyphae are shorter and have slower cytoplasmic flow rates and correspondingly slower growth rates.
Cytoplasmic streaming
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In many animal cells, centrioles and spindles keep nuclei centered within a cell for mitotic, meiotic, and other processes. Without such a centering mechanism, disease and death can result. While mouse oocytes do have centrioles, they play no role in nucleus positioning, yet, the nucleus of the oocyte maintains a central position. This is a result of cytoplasmic streaming. Microfilaments, independent of microtubules and myosin 2, form a mesh network throughout the cell. Nuclei, positioned in non-centered cell locations, have been demonstrated to migrate distances greater than 25 microns to the cell center. They will do this without going off course by more than 6 microns when the network is present. This network of microfilaments has organelles bound to it by the myosin Vb molecule. Cytoplasmic fluid is entrained by the motion of these organelles, however, no pattern of directionality is associated with the movement of the cytoplasm. In fact, the motion has been demonstrated to fulfill Brownian motion characteristics. For this reason, there is some debate as to whether this should be called cytoplasmic streaming. Nonetheless, directional movement of organelles does result from this situation. Since the cytoplasm fills the cell, it is geometrically arranged into the shape of a sphere. As the radius of a sphere increases, surface area increases. Further, the motion in any given direction is proportional to the surface area. So thinking of the cell as a series of concentric spheres, it is clear that spheres with larger radii produce a greater amount of movement than spheres with smaller radii. Thus, the movement toward the center is greater than the movement away from the center, and net movement pushing the nucleus towards a central cellular location exists. In other words, the random motion of the cytoplasmic particles create a net force toward the center of the cell. Additionally, the increased motion with the cytoplasm reduces cytoplasmic viscosity allowing the nucleus to move more easily within the cell. These two factors of the cytoplasmic streaming center the nucleus in the oocyte cell.
Cytoplasmic streaming
5184#9
Recently it has been proposed that the cytoplasm behaves like a glass-forming liquid approaching the glass transition. In this theory, the greater the concentration of cytoplasmic components, the less the cytoplasm behaves like a liquid and the more it behaves as a solid glass, freezing larger cytoplasmic components in place (it is thought that the cell's metabolic activity is able to fluidize the cytoplasm to allow the movement of such larger cytoplasmic components). A cell's ability to vitrify in the absence of metabolic activity, as in dormant periods, may be beneficial as a defence strategy. A solid glass cytoplasm would freeze subcellular structures in place, preventing damage, while allowing the transmission of very small proteins and metabolites, helping to kickstart growth upon the cell's revival from dormancy.
Cytoplasm
26051686#0
Cytoplasmic incompatibility (CI) is a phenomenon that results in sperm and eggs being unable to form viable offspring. The effect arises from changes in the gamete cells caused by intracellular parasites like "Wolbachia", which infect a wide range of insect species. As the reproductive incompatibility is caused by bacteria that reside in the cytoplasm of the host cells, it is referred to as cytoplasmic incompatibility. In 1971, Janice Yen and A. Ralph Barr of UCLA demonstrated the etiologic relationship of "Wolbachia" infection and cytoplasmic incompatibility in "Culex" mosquitos when they found that eggs were killed when the sperm of "Wolbachia"-infected males fertilized infection-free eggs.
Cytoplasmic incompatibility
656613#0
Cytoplasmic streaming, also called protoplasmic streaming and cyclosis, is where there is flow inside the cytoplasm. It is typically observed in large plant and animal cells. Here flow means that the cytoplasm is moving inside the cell, it is not stationary. The flow is driven by forces from the cytoskeleton, and it is likely that the function of flow is at least partly to speed up transport of molecules and organelles around the cell. Cytoplasmic streaming is usually found in unusually large cells, greater than approximately 0.1 mm. In smaller cells, diffusion of molecules will be rapid but diffusion slows rapidly as the size increases, and so larger cells may need flow to move nutrients etc inside them rapidly enough for efficient function.
Cytoplasmic streaming
5184#7
The physical properties of the cytoplasm have been contested in recent years. It remains uncertain how the varied components of the cytoplasm interact to allow movement of particles and organelles while maintaining the cell’s structure. The flow of cytoplasmic components plays an important role in many cellular functions which are dependent on the permeability of the cytoplasm. An example of such function is cell signalling, a process which is dependent on the manner in which signaling molecules are allowed to diffuse across the cell. While small signaling molecules like calcium ions are able to diffuse with ease, larger molecules and subcellular structures often require aid in moving through the cytoplasm. The irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm.
Cytoplasm
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The flow of the cytoplasm in the cell of "Chara corallina" is belied by the "barber pole" movement of the chloroplasts. Two sections of chloroplast flow are observed with the aid of a microscope. These sections are arranged helically along the longitudinal axis of the cell. In one section, the chloroplasts move upward along one band of the helix, while in the other, the chloroplasts move downwardly. The area between these sections are known as indifferent zones. Chloroplasts are never seen to cross these zones, and as a result it was thought that cytoplasmic and vacuolar fluid flow are similarly restricted, but this is not true. First, Kamiya and Kuroda, experimentally determined that cytoplasmic flow rate varies radially within the cell, a phenomenon not clearly depicted by the chloroplast movement. Second, Raymond Goldstein and others developed a mathematical fluid model for the cytoplasmic flow which not only predicts the behavior noted by Kamiya and Kuroda, but predicts the trajectories of cytoplasmic flow through indifferent zones. It should be noted that the Goldstein model ignores the vacuolar membrane, and simply assumes that shear forces are directly translated to the vacuolar fluid from the cytoplasm. The Goldstein model predicts there is net flow toward one of the indifferent zones from the other. This actually is suggested by the flow of the chloroplasts. At one indifferent zone, the section with the chloroplasts moving at a downward angle will be above the chloroplasts moving at an upward angle. This section is known as the minus different zone (IZ-). Here, if each direction is broken into components in the theta (horizontal) and z (vertical) directions, the sum of these components oppose each other in the z direction, and similarly diverges in theta direction. The other indifferent zone has the upwardly angled chloroplast movement on top and is known as the positive indifferent zone (IZ+). Thus, while the z directional components oppose each other again, the theta components now converge. The net effect of the forces is cytoplasmic/vacuolar flow moves from the minus indifferent zone to the positive indifferent zone. As stated, these directional components are suggested by chloroplast movement, but are not obvious. Further, the effect of this cytoplasmic/vacuolar flow from one indifferent zone to the other demonstrates that cytoplasmic particles do cross the indifferent zones even if the chloroplasts at the surface do not. Particles, as they rise in the cell, spiral around in a semicircular manner near the minus indifferent zone, cross one indifferent zone, and end up near a positive indifferent zone. Further experiments on the Characean cells support of the Goldstein model for vacuolar fluid flow. However, due to the vacuolar membrane (which was ignored in the Goldstein model), the cytoplasmic flow follows a different flow pattern. Further, recent experiments have shown that the data collected by Kamiya and Kuroda which suggested a flat velocity profile in the cytoplasm are not fully accurate. Kikuchi worked with "Nitella flexillis" cells, and found an exponential relationship between fluid flow velocity and distance from cell membrane. Although this work is not on Characean cells, the flows between "Nitella flexillis" and "Chara coralina" are visually and structurally similar.
Cytoplasmic streaming