Why does ionizing radiation cause only DNA double strand breaks?
Ionizing radiation, such as X-rays or gamma rays, has the ability to cause damage to biological molecules. Among the different types of radiation-induced damage, DNA double strand breaks (DSBs) are considered the most critical and potentially harmful.
1. Energy deposition: When ionizing radiation passes through living tissue, it transfers energy to the molecules it interacts with. This energy deposition is crucial for causing DNA DSBs. Unlike non-ionizing radiation, which lacks sufficient energy to break chemical bonds, ionizing radiation carries enough energy to produce highly reactive and damaging particles called ions, which can directly break the DNA molecule
2. Direct ionization: Ionizing radiation can directly ionize DNA molecules, leading to the formation of highly reactive and destructive free radicals. These free radicals, such as hydroxyl radicals (•OH), can directly attack the phosphate backbone or the sugar moieties of the DNA double helix, causing breaks in both DNA strands
3. Indirect ionization: Ionizing radiation can also indirectly cause DNA DSBs through a process called radiolysis of water. When water molecules are exposed to ionizing radiation, they can be ionized and produce reactive oxygen and hydrogen species, such as hydroxyl radicals (•OH) and peroxyl radicals (ROO•). These radicals can diffuse through the cell and react with DNA, resulting in DSBs
4. Complexity of DNA structure: The DNA molecule is composed of a double helix, where two strands are intertwined. This structural feature makes the DNA molecule more susceptible to DSBs. When a DSB occurs, both strands of the DNA molecule are severed, leading to the loss of genetic information and potentially causing serious cell damage or death
It is important to note that while ionizing radiation primarily causes DNA DSBs, it can also induce other types of DNA damage, such as single strand breaks (SSBs), base modifications, or damage to DNA-associated proteins. These additional types of damage can contribute to the overall biological effects of ionizing radiation, but DSBs are generally considered the most deleterious type of DNA damage, as they are difficult for cells to repair accurately
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