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The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
Cells are least sensitive when in the S phase, then the G 1 phase, then the G 2 phase, and most sensitive in the M phase of the cell cycle.This is described by the 'law of Bergonié and Tribondeau', formulated in 1906: X-rays are more effective on cells which have a greater reproductive activity.
Radiation used for cancer treatment is called ionizing radiation because it forms ions in the cells of the tissues it passes through as it dislodges electrons from atoms. This can kill cells or change genes so the cells cannot grow. Other forms of radiation such as radio waves, microwaves, and light waves are called non-ionizing.
Radiation exposure through ionizing radiation (IR) affects a variety of processes inside of an exposed cell. IR can cause changes in gene expression, disruption of cell cycle arrest, and apoptotic cell death. The extent of how radiation effects cells depends on the type of cell and the dosage of the radiation.
S phase (Synthesis phase) is the phase of the cell cycle in which DNA is replicated, occurring between G 1 phase and G 2 phase. [1] Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved.
The different stages of mitosis all together define the M phase of an animal cell cycle—the division of the mother cell into two genetically identical daughter cells. [3] To ensure proper progression through the cell cycle, DNA damage is detected and repaired at various checkpoints throughout the cycle.
Recent research has proposed the idea that HeLa cells damaged with radiation (cells that are unique in that they have short-shouldered survival curves and two peaks of radio resistance during the cell cycle phase) show the fact that radio-suppression is mediated by intra-s checkpoints and reduces survival of cells in the s-phase.
Tumor cells in a hypoxic environment may be as much as 2 to 3 times more resistant to radiation damage than those in a normal oxygen environment. [5] Much research has been devoted to overcoming this problem including the use of high pressure oxygen tanks, blood substitutes that carry increased oxygen, hypoxic cell radiosensitizers such as ...