Use of Radioisotopes in Biological Research - When most people think of radiation, they usually picture it in its most destructive form that emitted from a nuclear bomb. However, controlled radiation has its positive uses. As we discuss in this chapter, all atoms of an element have the same number of protons and electrons. However, not all atoms of a given element have the same atomic mass (remember that mass equals the number of protons plus the number of neutrons). For example, the most common mass number of hydrogen is 1H, because it has only one proton in its nucleus. Sometimes, however, hydrogen also has a neutron in addition to its proton; hence its mass is 2H, and it is called deuterium. In other instances, hydrogen has two neutrons, so it has a total mass of three (3H). This isotope is called tritium.
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| Radiosisotopes in Biology |
Multiple forms of the same element, which are due to a change in the number of neutrons in the nucleus, are called isotopes. Some isotopes are unstable that is, they decay, or change to achieve a more stable form. To decay, isotopes spontaneously give off energy or subatomic particles. In other words, they emit radiation, which is why they are called radioisotopes. Tritium (3H) or carbon 14 (14C) are two radioisotopes that you may have heard of. The released energy or subatomic particles can be detected by various counting instruments, such as Geiger counters or devices like photographic film. Their detectability makes them extremely valuable in biological research.
One of the major uses of radioisotopes is to label, or ''tag," a molecule. You can label any molecule with radioactive isotopes and then trace its pathway through a cell or organism. For example, let's say that you allow a bean plant to take up radioactive phosphorus (32P) through its roots for a period of time. If you then press the plant onto a sheet of flat photographic film in the dark, the radiation emitted by the radioisotopes will develop the film, revealing the path that the liquid has taken through the plant. This process, called autoradiography, is a useful technique for locating the position of a radioactive substance.
Radioisotopes can be used to study many molecular processes. For example, if researchers inject radioactive amino acids (the molecular subunits that make up proteins) into a growing organism or cell, they can then isolate proteins from various tissues and find the proportion that are radioactive. This will help them determine the rate of protein synthesis. Radioisotopes are also very useful in medicine, not only as diagnostic tools but also as a means
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