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Evaluation of Escherichia coli cells damages induced by ultraviolet and proton beam radiation. Prokaryote cells were exposed to ultra violet UVc radiation and to proton beams in order for the induced effects to be studied.
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Morphological and physiological alterations occurred in Escherichia coli E. An exposition time of 3 to 15 seconds for UVc radiation and dose ranging from 0. A cellular survival curve versus exposition time and absorbed dose was built for each case.
After the irradiation the cells were submitted to a series of biochemical tests. It was observed that the E.
Coli cells lost some basic biochemical properties when the received doses were in the range of 0. By microscopic observations it was noticed that the E. Coli cells elongated after irradiation with UVc as well as with proton beam.
The prokaryotes compose an interesting group of microorganisms, which can be used as instruments of scientific investigation. This can be explained by the fact that they possess intrinsic properties, such as reduced time of generation and relatively low cost of culture and maintenance , .
Livro Biofísica Básica – Ibrahim Felippe Heneine
The Escherichia coli E. It is an important biotechnological tool, which makes it possible to obtain important parameters for the metabolic and genetic characterization of cells of more complex organisms.
The ionizing and not ionizing radiations can cause mutations through direct or indirect action on the cellular surface. Some mutations are undesirable and even lethal, however, heneind can be interesting for the survival of a species , , .
At the present work possible transformations on E. This can be provoked by UVc radiation that induces the formation of pyrimidine dimers in the cellular DNA or by beams of protons it can dislocate electrons of the atoms and create highly reactive ions that can attack bipfisica constituents of the cell, including the DNA , .
The occurrence of morpho-physiologic alterations in the cells of E. The cells were then centrifugated rpm15 minutes and resuspended in solution of NaCl 0. This solution was used to make the dilutions of which 0. For the irradiation with UVc radiation a dilution of 1: The Petri plates triplicate which contain the microorganisms in Agar MacConkey were irradiated , For ultra violet radiation, an exposition time of 3 to 15 seconds was used in a laminar flow chamber.
For the radiation with proton beams the absorbed doses ranged from 0. For each of the radiation types UVc and protons a survival curve that relates the survival fraction with the exposition time or the absorbed dose by the cells was made , .
The radiated cells were then submitted to biochemical tests and also to microscopic analysis Gram-stain in optical microscope magnification of x. The biochemical test carried out was the following: Vogues-Proskauer, Indol production, descaboxilation of L-lisina, glucose fermentation, lactose fermentation, rhamnose fermentation, urea hydrolysis, H 2 S production, citrate and ornitine , .
The average number of CFU for each exposition time was calculated through equation 1 concerning survival fraction FSwhere N represents the CFU after each irradiation and N 0 corresponds to the CFU in plates not exposed to radiation , : Figure 1 shows the plot of the survival fraction versus the exposition time to the UVc beam, while Fig.
In the Gram-stain the E. The microscopical studies showed that the E. As for the exposition with proton beam, it was also possible to observe that the cells were elongated as can be seen in Figs. In the literature the elongation phenomenon of E. This antibiotic intervenes in the synthesis of the peptidoglycan of the cell’s wall, resulting in the incapacity of the cell to divide, without provoking its death .
The existence of the so called hormesis phenomenon is also registered, with stimulated or benefic effect, induced by low doses of a radioactive agent. The concept of hormesis radiation is normally applied to radiation doses in the range of 1 to 50 Gywhich means, radiation doses that instead of provoking irreparable damage that would lead to cellular death, would provoke a radioadaptative response that would benefit the cell and its descendant , .
In the present work it was verified that the E. With the experiments described above it was possible to conclude that: The tests should be rechecked and it would perhaps be necessary to increase the corpuscular radiation dose proton beams applied to the E. Curso Superior de Tecnologia em Radiologia. Menezes, Tratado de Microbiologiap. Mortazavi, An Introduction to Radiation Hormesis.
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