|
The G1 phase, or Growth 1/Gap 1 phase, is the first of four phases of the cell cycle that takes place in eukaryotic cell division. In this part of interphase, the cell synthesizes mRNA and proteins in preparation for subsequent steps leading to mitosis. G1 phase ends when the cell moves into the S phase of interphase. == Overview == G1 phase together with the S phase and G2 phase comprise the long growth period of the cell cycle called interphase that takes place before cell division in mitosis (M phase).〔Lodish, Harvey, et al. Molecular Cell Biology. 6th. New York City: W.H. Freeman and Company, 2008. Print.〕 During G1 phase, the cell grows in size and synthesizes mRNA and proteins that are required for DNA synthesis. Once the required proteins and growth are complete, the cell enters the next phase of the cell cycle, S phase. The duration of each phase, including the G1 phase, is different in many different types of cells. In human somatic cells, the cell cycle lasts about 18 hours, and the G1 phase takes up about 1/3 of that time.〔Morgan, David. The Cell Cycle: Principals of Control. London: New Science Press LTD, 2007. Print.〕 However, in Xenopus embryos, sea urchin embryos, and Drosophila embryos, the G1 phase is barely existent and is defined as the gap, if one exists, between the end of mitosis and the S phase.〔 G1 phase and the other subphases of the cell cycle may be affected by limiting growth factors such as nutrient supply, temperature, and room for growth. Sufficient nucleotides and amino acids must be present in order to synthesize mRNA and proteins. Physiological temperatures are optimal for cell growth. In humans, the normal physiological temperature is around 37 °C (98.6 °F).〔 G1 phase is particularly important in the cell cycle because it determines whether a cell commits to division or to leaving the cell cycle.〔 If a cell is signaled to remain undivided, instead of moving onto the S phase, it will leave the G1 phase and move into a state of dormancy called the G0 phase. Most nonproliferating vertebrate cells will enter the G0 phase.〔 While in the G1 phase of the cell cycle, a cell is haploid or 1n. This means that the cell contains one set of the organism’s DNA. The genetic material exists as chromatin, or loosely bundled strands of DNA. Diploid eukaryotic organisms such as yeast are 2n and will have one set of DNA until S phase is complete.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「G1 phase」の詳細全文を読む スポンサード リンク
|