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The stages of interphase are: G 1 (Gap 1), in which the cell grows and functions normally. During this time, a high amount of protein synthesis occurs and the cell grows (to about double its original size) – more organelles are produced and the volume of the cytoplasm increases. If the cell is not to divide again, it will enter G 0. [3]
The G 1 phase, gap 1 phase, or growth 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. G 1 phase ends when the cell moves into the S phase of interphase.
The G1/S transition is highly regulated by transcription factor p53 in order to halt the cell cycle when DNA is damaged. [ 5 ] It is a "point of no return" beyond which the cell is committed to dividing; in yeast this is called the Start point , and in multicellular eukaryotes it is termed the restriction point (R-Point).
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.
The cell cycle in eukaryotes: I = Interphase, M = Mitosis, G 0 = Gap 0, G 1 = Gap 1, G 2 = Gap 2, S = Synthesis, G 3 = Gap 3. Cell division is the process by which a parent cell divides into two daughter cells. [1] Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing.
Steps of the cell cycle. The restriction point occurs between the G 1 and S phases of interphase.. The restriction point (R), also known as the Start or G 1 /S checkpoint, is a cell cycle checkpoint in the G 1 phase of the animal cell cycle at which the cell becomes "committed" to the cell cycle, and after which extracellular signals are no longer required to stimulate proliferation. [1]
Figure 1: Schematic of the cell cycle. outer ring: I = Interphase, M = Mitosis; inner ring: M = Mitosis, G 1 = Gap 1, G 2 = Gap 2, S = Synthesis; not in ring: G 0 = Gap 0/Resting. Replication timing refers to the order in which segments of DNA along the length of a chromosome are duplicated.
Upstream transcription factors are proteins that bind somewhere upstream of the initiation site to stimulate or repress transcription. These are roughly synonymous with specific transcription factors, because they vary considerably depending on what recognition sequences are present in the proximity of the gene. [94]