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The chemical safety cabinet is characterized by an aspiration system which, by sucking air from the environment through the front working opening, determines an air flow triggered and maintained by an electric aspirator, it enters the work chamber bounded by the screen and the work surface. The front speed of the intake air must not be less than 0.5 meters per second; these values refer to 40 centimeters of front opening and are to be checked on an annual basis. When the prefix is added to the hypotonic cells, a change in color from red to brown is observed because the red blood cells that burst release the iron contained in the eme and it oxidizes. Resuspend well with a plastic pasteur. At the end the supernatant is removed and the pellet is well resuspended. Now add the methanol which starts the first fixation and dehydration of the cells. The purpose of fixation is to preserve the structures of the cells in their morphological state, blocking their degradation, after the block and following the variation in temperature and pH. Fixation must preserve the samples from the attack of mold and bacteria and best preserve the structural and ultrastructural morphology of the tissue and cell and also allow the preparation to withstand the physical and chemical stresses of the subsequent preparation stages of the preparation. In general, it can last from a few minutes up to 24 - 48 hours. The cells in methanol are well resuspended and the tubes are heated to -20 ° Celsius for at least 30 minutes. After at least half an hour in the freezer, the methanol cells are centrifuged again at 2100 repetitions per minute for 5 minutes At the end the methanol supernatant is removed. And we proceed with the actual fixation. The pellet is well resuspended. The fixative is prepared. The Carnoy mixture (consisting of methanol: acetic acid in a 3: 1 ratio) is used as a fixative in the preparation of the metaphasic plates. This mixture blocks cellular functions and prevents further enlargement of cells, stabilizes the structure of chromosomes, otherwise fragile, removes proteins, preserves cell morphology, dehydrates the preparation making it more durable, delaying the action of agents oxidants (methanol). The cytoplasm, in which the chromosomes are immersed, is dehydrated by alcohol and reduced by acetic acid. It should be borne in mind that if acetic acid does not work well because of the humidity in the air or because it has been open for too long, its disruptive action does not take place. This means that the preparations always remain with the cytosol-nuclear matrix, and the chromosomes are still too condensed and small and therefore difficult to see under the microscope. Chemical fixatives are divided into: primary coagulative fixatives which represent a class of molecules capable of crossing the cell membrane, inside the cell determine the denaturation of proteins, with a coagulating effect. Among the main ones we find alcohol (ethanol and methanol). and non-coagulant primary fixatives which block the activity of proteins without causing their precipitation. Among the main ones we find acetic acid. A new centrifuge is always made at 2100 repetitions per minute for 5 minutes. By starting the centrifuge, the cross will rotate on its axis of symmetry and if a heterogeneous solution is found inside the tubes, the action of the centrifugal force will push the solid towards the bottom of the tube, separating the solid from the liquid phase. There are different types of centrifuges that can be used for different purposes. The joint centers can have fixed angle, vertical and swinging arm rotors. What we see is a bench top centrifuge with oscillating arm rotor. In the rest position, the tubes remain in a vertical position, but when the rotor starts to rotate, following centrifugal acceleration, the tubes rotate outwards on the pins, positioning themselves horizontally. At the end the supernatant is removed and the pellet is resuspended. The fixative (consisting of methanol: acetic acid in a 3: 1 ratio) is added for the last time. Work continues under a chemical safety cabinet Which is an externally (or conventional) ducted safety cabinet, it has an external electric fan in a remote position at the end of the expulsion duct, it is equipped with filter groups such as chemical absorption traps, activated carbon filters. The tubes are housed in the cruise and a centrifuge is made at 2100 rpm for 5 minutes.Swing arm rotors such as this permit the formation of well separated precipitate bands, but are more delicate than fixed angle rotors. This has a maximum speed of around 15000 rpm. They are used to isolate materials that quickly sediment and centrifuge relatively small volumes (up to 50milliliters). At the end the supernatant is removed and the pellet is well resuspended. The fixative is prepared, consisting of methanol: acetic acid in a 2 to 1 ratio.