Prions are altered forms of proteins that are naturally produced in nerve cells and certain other cell types. Production of these normal proteins is illustrated from the nucleus at bottom right. When these "normal" proteins meet the rogue prions (purple) the normal protein changes shape to match the shape of the prions. It is this shape-flipping which is equivalent to the transmission of infection. Prions polymerise, finally appearing as purple fibrils in the picture. Prions could enter the brain along the axons of neurons, shown in the picture as purple spheres ascending the axon like elevators going up a shaft . Another route of entry could be the blood, probably in immune cells. A lymphocyte is shown exiting the capillary at bottom left where it could then contact the astrocyte. Astrocytes and other glial cells also support the production of prions.
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This plant cell is surrounded by at least four other similar type of cells and has a cellulosic cell wall stained dark blue. It contains a large vacuole in which lightly stained granular matter is visible. The nucleus lies at the upper right and is vesicular (baloon-like). Its nuclear membrane is dotted by darkly stained material called chromatine on which the genetic material is embedded. The nucleus is apparently not empty and contains a moderately well-stained network. But the nucleolus, the dark-blue stained, massive, spherical structure, is the most prominent part of the nucleus. The stained portion around the nucleus is the cytoplasm. The cells illustrated are from a potato, Solanum tuberosum. A very thin section, 2 µm, Toluidine blue (1% aqueous solution) staining.
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