同位素示踪法（Isotope tracer method）

同位素示踪法（Isotope tracer method）Application of isotope tracer method in biology experiment in Senior High SchoolThe isotope tracer method is the use of radionuclide tracer labeled as trace analysis method to the research object, namely the radioactive isotope atoms to other substances to participate, let them move together, then the migration of radioactive detecting instrument for tracking, you can know what the radioactive atom movement path, where, what is the distribution of. The isotope tracing method is an important method is often used in biological experiments, it can be the source, the study of the intracellular elements or compounds of the composition, distribution and fate, and to understand the cellular structure and function, chemical change and reaction mechanism. Radioisotope used in tracer technology is generally used as an important element in the formation of cell compounds such as 3H, 14C, 15N, 18O, 32P, 35S, 131I, etc. In high school biology textbooks, there are many related to the application of radioisotopes. The following are summarized as follows:1 study the material and process of protein or nucleic acid synthesisThe reflective atomic parameters to synthesis of protein or nucleic acid material (amino acid or nucleotide), let them move together, then the migration of radioactive detecting instrument for tracking, you can know what the radioactive atom path, where and how the distribution of sports.2 to study the synthesis and transport of secreted proteinsUsing leucine labeled with 3H to investigate the synthesis, transport and secretion pathway of secretory proteins in cells. Given the premise of radiolabelled amino acids in disposable, by radioactive substances in cells were detected in different time position, you can clearly see that the organelle in the secretory protein synthesis and transport effect. For example, after the synthesis of protein in the endoplasmic reticulum attached to the ribosome through experiments that the secretion is in accordance with the cell membrane, endoplasmic reticulum and Golgi the direction of transport, so that all cells within biofilms in function are closely linked.3 study the structure and function of cellsUsing isotope labeling of amino acids or nucleotides and introducing them into cells, it is possible to detect which structures these radioactive markers appear in, thereby inferring the structure and function of the cells.4 explore the transfer of elements in photosynthesisUsing radioisotope 18O, 14C and 3H as tracer atoms to study the changes of some substances during photosynthesis, and to reveal the mechanism of photosynthesis. For example, American scientists Lubin and Carmen studied whether oxygen released from photosynthesis comes from water or from carbon dioxide. They use the oxygen isotope 18O were labeled with H2O and CO2 respectively, so that they become H218O and C18O2, and then two groups: the first group to the photosynthesis of green plants with H218O and CO2, second groups of H2O and C18O2 to provide the same green plants. Under the same conditions, they analyzed two groups of photosynthesis release oxygen. The results show that the first release of oxygen are 18O2, second groups of oxygen are O2, which proved that the release of oxygen from water photosynthesis. In addition, Calvin and other 14C labeled CO2 were used for photosynthesis of Chlorella vulgaris, and their radioactivity was tracked. The pathway of carbon in CO2 converted into organic carbon in photosynthesis was examined.5 to study the pathway of substance change during cell respirationUsing 18O as tracer atom, we study the pathway of substance change in cell respiration, and reveal the mechanism of respiration. For example, the oxygen produced by 18O tagged oxygen (18O) is radioactive, and all the carbon dioxide produced is free of radioactivity, that is, 18O to H218O. With 18O labeled glucose (C6H1218O6), all the carbon dioxide generated is radioactive, and the generated water is free of radioactivity, that is, C6H1218O6 to C18O2. For example, an experimental mouse is placed in a container containing radioactive 18O2 gas, and when 18O2 enters the cell, the first radioactive compound is water.6 to study the absorption and transportation of certain mineral elements in plantsStudy on mineral elements absorption site, commonly used radioisotopes such as 32P to do the experiment, found the root resorption of the root hair zone is the most active part of mineral ions. Transport sites of mineral ions in the stem when the impervious separates the stencils of willow phloem and xylem, and in soil application with 42K fertilizer, determination of the distribution of 42K in different parts of willow stems after 5 hours; a stencil separated xylem phloem contains a lot of 42K, almost no 42K that is, the transport of 42K in the xylem; willow stems in the following section with paper from the phloem and xylem and the stencil is not inserted in the phloem of the control experiment, there are a lot of 42K 42K from xylem to phloem transverse transport.7 to study the changes of chromosomes during mitosisIn the continuous division of the cell division stage labeled with 3H thymidine, according to thymine utilization situation, can determine the starting point DNA synthesis phase and duration, in order to study the changes of chromosomes during mitosis. For example, in order to verify the mitogenic substances on the cell division to promote the role of the liver cell suspension mice into cell number two groups A and B with 3H labeled thymidine in liquid culture in group A (3H-TdR); group B with dose of 3H-TdR added to promote silk division of material. After a period of culture, the total radioactivity of the two groups of cells was measured. Again, someone to determine the length of time the DNA synthesis phase, continuous splitting in mitosis with 3H labeled thymine, thymine is according to the use, can determine the starting point and duration of DNA synthesis.8 prove that DNA is a genetic materialIn the study of protein and DNA in the role of genetic elements, characteristics of radiolabeled protein and DNA respectively, using 32P labeled phage DNA, radioactive substances found in Escherichia coli, labeled with 35S phage protein, found no radioactive material from Escherichia coli; verify the phage during the infection of bacteria, the bacteria enter the body is not DNA phage, phage protein, and prove that DNA is the genetic material of the phage.9 to explore the characteristics of DNA molecular semi reserved replication15N is used to distinguish between parent and offspring DNA, such as radiolabeled 15N, because the atomic mass of the radioactive substance is different from the atomic weight of 14N, so the relative molecular weight of DNA is different. If the two chains of DNA is 15N, then the centrifugal heavy belt; if a chain of DNA molecule is 15N, a chain is 14N, it is with centrifugal; if the two chains of DNA are 14N, then when the light with centrifugal. Therefore, it is possible to determine whether DNA replication is fully reserved or semi reserved replication based on the ratio of the bands, bands, bands, and bands of DNA.10 explore the transcription and translation of genesUsing radiolabeled DNA RNA (feature base RNA U), amino acid, in the product of gene transcription, translation will contain radioactive isotope, can also be used to determine the transcription and translation of the place.Application of 11 gene probe in gene diagnosisIn gene diagnosis using DNA molecular radioactive isotope 15N and 32P markers as gene probe, a pathogenic gene was amplified in culture medium containing radioactive 15N or 32P, the heating to be labeled as single genes by DNA gene probe, hybridization principle, will be measured by DNA molecules heat treatment to form a single stranded DNA molecule and gene probe for hybridization, hybrid, detect whether two chain form, if fully formed double chain, prove that the blood of people with the disease, otherwise do not suffer from. The gene diagnosis method can rapidly detect hepatitis viruses, enteroviruses and other viruses, as well as sickle cell anemia, phenylketonuria, leukemia, etc. According to the hybridization band, it is possible to detect the biological relationship or whether the inserted gene is inserted into the target gene, and the same principle can also be used to detect the content of virus in drinking water.For example, the scientific workers in China use the principle of DNA molecular hybridization and develop a SARS diagnostic kit using genetic engineering to rapidly diagnose sars.12 application in biological mutagenesis breedingMutation breeding is the use of X ray, gamma ray, beta ray or neutron irradiation to crop seeds, plants or some organs, which makes their genetic changes, mutations produce a variety of useful to obtain mutants in a relatively short period of time, and then choose from a mutation is useful to humans, the new after a variety bred. The commonly used radioactive isotopes in mutagenic breeding include 35S, 32P, 45Ca (beta ray), 65Zn, 60Co (gamma ray) and so on. The main methods are soaking seeds, applying soil, applying seedlings and injecting into plant tissues. If it is a typical gamma radiation source, it can be used for mutation breeding. Many new crop varieties have been cultivated by this method in china. Such as cotton high-yielding variety Lu cotton No. 1, the annual planting area has reached about 30000000 acres, the cultivation of cotton varieties in China, the largest cultivation area.13 explore the functions of the cerebral cortexScientists often use PET technology to locate the advanced functions of the cerebral cortex. PET technology is a reflection type. Electronic computer tomography imaging technique is a direct imaging of brain function technology, using this technology, scientists can determine the consumption of brain to regional material by detecting element special, different functional areas and to locate the cerebral cortex. The basic elements of glucose (C, H, O) with radioactive ultrashort life (such as F18, C11 etc.), made of radioactive tracer, and then put the tracer injection to the subjects blood vessels, through the detection of components specially designed, can obtain the three-dimensional distribution of tracer in the subjects brains and varies with time. If subjects were thinking, language, listening, writing and other advanced functions, corresponding to the central cortex in a highly excited state, at the same time, through the observation of the consumption of these tracers central location and distribution can be obtained in various functional areas of the cerebral cortex. For example, when subjects are written, the centers of writing in the cerebral cortex consume large amounts of glucose, and the location of the nerve center can be located by detection. At present, this technique has been widely used in the diagnosis and differential diagnosis of various diseases, the diagnosis of disease, the evaluation of curative effect, the study of organ function and the development of new drugs.14 study the feedback regulation mechanismIn biological feedback regulation, the change of a substance causes a series of regulatory reactions, and also leads to the corresponding changes of other substances. To mark a substance, treat it in a certain way, and study the mechanism of feedback regulation by detecting the amount of radioactive material in an organ. For example, in the study of thyroid gland and thyroid hormone and thyroid stimulating hormone secretion, 131I is usually used for isotopic tracer labeling. Because the iodine absorbed by the body from food is almost exclusively concentrated in the thyroid gland, which is used to synthesize thyroid hormones.15 application in immunoregulationAn antigen labeled with a high dose of isotope to an animal results in not only immune response but also subsequent immune responses to the same but different isotope labeled antigens. At this point, normal immune responses can also occur in animals given other antigens. The experiment showed that the isotope labeled antigen was combined with lymphocytes with complementary antibodies, which were all killed by radiation, so no immune response occurred. Second times to the same normal antigen, antibody with complementary lymphocytes have all been killed, although other types of lymphocytes to other antigens can normal reaction, but not react to this antigen, which can not change with the complementary lymphocyte antigen. As a result, animals lose immunity to this antigen. Thus, the specificity of lymphocytes is innate, not by the instruction of antigens.16 to study the polar transport of auxinThat plant polar auxin transport, with isotope 14C labeled stem morphological upper auxin (IAA), in stem morphological part of detected radioactive isotope 14C, and morphological markers of stem at the lower end of the auxin, in upper stem morphology not detect radioactive isotopes that auxin only from the morphology of the upper end transport to morphology.17 study the problems of material circulation and energy flowIn ecosystems, elements such as C, H, O, N, P, and S that constitute organisms continue to cycle from the inorganic environment to the biological community, and from the biotic community to the inorganic environment. If these elements are involved in the material circulation using radioisotope markers, the pathway of material transfer can be traced. For example, the 35S marker SO2 and the 14C marker CO2 were used to track the sulfur cycle and the pathways of S and C transfer in the carbon cycle.In short, the isotope tracer method are applied to large-scale biological research field, as a high school biology teacher, understand the relevant knowledge and experimental isotope labeling techniques more, will develop their own knowledge, construct the knowledge support itself is solid, teaching appropriate original experimental teaching some isotope labeling techniques, is conducive to the complex knowledge and biology is more scientific and more primitive to teach students, at the same time, also enable the students to have a more profound understanding of the technology and grasp.Application of radioisotope tracer method in biology of senior high schoolAbstract radioisotopes are widely used in biological studies, such as the DNA is a genetic material, a semi reserved copy of DNA, a genetic diagnosis, and the transport of mineral elements. C4 pathway of plant photosynthetic pathway, auxin transport, secretion, synthesis and transport of proteins, photosynthesis, and the atomic transfer of respiration.Keywords radioisotope; semi conservative replication; C4 pathway; secreted protein; gene diagnosis;First, isotope tracing proved that DNA is a genetic substanceIn bacteriophage impregnated bacteria experiments, phages have only two substances: DNA and protein. From the component elements, DNA contains C, H, O, N, P, while the protein contains C, H, O, N, S and so on. Moreover, P mainly exists in DNA, while S mainly exists in the protein coat, and 35S and 32P are used to mark proteins and DNA respectively, which can directly and individually observe which substances are genetic substances in the endTwo, to study the characteristics of semi reserved replication of DNAAre DNA copies of total retention, replication, half retention replication, or diffusion replication? We can use isotope tracer method to do research. We mark the DNA with 15N and then provide the raw material for 14N to replicate. How many chains of 14N and 15N are present in the F1, F2, and F3 generations of DNA? The isotope tracer method is very clear:DNA: in the first replication, forming two DNA molecules, namely four chains, two chain chain containing 15N, two with 14N, second copies, 4 DNA molecules, namely eight chains: including 15N two, 14N 6. After third replicates, eight DNA molecules, namely 16 strands, containing two 15N and 14 14N, were obtained. That is, no matter how many times DNA copies are made, the template chains containing 15N are only 2, and the rest are chains containing 14N. This result is obtained by centrifugation with density gradient centrifugation.Therefore, whether isotope replication was used to study DNA replication or density gradient centrifugation after replication, DNA was proved to be semi reserved replication.Three. Application of isotope tracer method in gene diagnosisIn gene diagnosis can be prepared by using radioisotope 15N gene probe and 32P system, the disease gene was amplified in the medium containing 15N or 32P, is heated to 80 C and 120 C, namely single marker genes by DNA probe, using the principle of DNA hybridization,The test of the DNA heat treatment to form a single stranded DNA molecule molecule and gene probe mixed, after cooling to hybridization, detecting whether the formation of double chain, if fully formed double chain, prove that the test subjects with a genetic disease or no disease.Four. Study the transfer of mineral elements in plantsWith 32P fertilizer long-term cultured in nutrient solution in the plant, and then put the plant in nutrient solution without 32P, 32P to transport was reduced, and the old leaves to freshman Ye Yunshu, indicating that P can be transferred, can be re used elements.Five. Study the pathway of photosynthesis in C4 plantsThe 14CO2 isotope labeling, and then the supply of plant photosynthesis, the marker of metastasis is 14CO2 - 14C4 - 14C3 - 14C6H12O6, CO2 was first formed in four fixed carbon compounds, and then transferred to three carbon compounds, was finally reduced to glucose.Six. Study the polar transport of auxinWith the agar block containing 14C labeled auxin, morphology is placed above the truncated, the lower end can be detected in morphological markers, in turn, the agar block containing 14C labeled auxin on the morphology of the lower end of the upper end is not detected in morphological markers radioactive, indicating that auxin only by upper transport morphology the plant body to the lower, but not by the morphology of the lower to the upper end transport morphology.Seven. Study the physical cycle of natureThe 15N fertilizer is applied to the soil, providing the plant with the direction of the soil, the plant, the animal body, the soil, indicating that the elements that make up the organism are constantly recycled between the organism and the inorganic environment.Eight. Using the amino acids labeled with 15N, the site of the synthesis and secretion of amino acids, the transport channel and the secretion process of amino acids were studied.Labeled with 15N leucine supply of pancreatic cells, and the radioactive material transfer pathway is a leucine (15N), ribosomal (15N), endoplasmic reticulum (15N) vesicles, (15N), Golgi vesicles (15N), (15N), cell membrane (15N) and extracellular (15N)This not only indicates the direction of the synthesis and transport of secretory proteins, but also shows the close division of functions of various biological membranes and the formation of a whole.Nine. Study the fate of elements in photosynthesis and cellular respiration by using radioactive elements.The release of O2 from photosynthesis results from photolysis of water.Therefore, the development of physics and chemistry, to promote the development of biology, I believe in the future development of biology, physics and chemistry technology will be more widely used in biology, as the development of biology, to make a greater contribution to the development of biological technology.