Application of Isotope Labeling in Biology of Senior High School

Application of isotope labeling method in senior high school biology;

1, the source of oxygen in photosynthesis

1939, Rubin and Carmen labeled H2O and CO2 with 18O respectively, and then two groups of comparative experiments were conducted: one group provided H2O and C 18O2, and the other group provided H2 18O and CO2. Under the same other conditions, the oxygen released by the first group is O2, and the oxygen released by the second group is 18O2, which strongly proves that O2 released by plants comes from H2O instead of CO2.

2. Semi-conservative replication of 2.DNA

1957, American scientists meselson and Steiner cultivated E.coli in a medium containing 15N, making it a "heavy" bacterium, and then put it in a medium containing 14N for further cultivation. Samples were taken at different times and DNA was extracted for density gradient centrifugation. According to the difference of buoyancy between light chain and heavy chain, new chain and mother chain were separated, which confirmed the semi-retention of DNA replication.

3. Synthesis and secretion of secreted proteins

In 1970s, scientists such as jameson injected 3H-labeled leucine into pancreatic cells of guinea pigs. After 3 minutes, the labeled leucine appeared in the endoplasmic reticulum with ribosomes. 17min later appeared in Golgi apparatus; 1 17min later, it appears in vesicles near the inner side of cell membrane and is released into extracellular secretions. Thus, the synthesis and secretion pathway of secretory protein was found: ribosome → endoplasmic reticulum → Golgi apparatus → vesicle → cell membrane → efflux.

4. Formation of organic matter in photosynthesis.

In the 1940s, Calvin, an American biologist, briefly exposed Chlorella monocytogenes to CO2 containing 14C, and then ground the cells to analyze which compounds 14C appeared in. After 10 years' efforts, photosynthesis-calvin cycle's "three-carbon approach" was finally explored. For this, Calvin won the Nobel Prize.

5. Experiment of bacteriophage infecting bacteria

In 1952, hershey and Chase used T2 phage as experimental materials, labeled the protein shell and DNA of the phage with 35S and 32P respectively, and then infected E.coli with two kinds of phage labeled with 35S and 32P respectively. After centrifugation, analyze the position of radioactive materials. This experiment strongly proves that DNA is genetic material.

6. Genetic engineering

In the detection and identification of the target gene, DNA molecular hybridization technology (such as 32P) is adopted. The genomic DNA of transgenic organisms was extracted, and the DNA fragment containing the target gene was labeled with radioisotope and hybridized with the genomic DNA as a probe. If the hybridization band is displayed, it indicates that the target gene has been introduced into the recipient cell.