thumb|upright=1.35|Diagram of the G<sub>1</sub> phase
The G<sub>1</sub> 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<sub>1</sub> phase ends when the cell moves into the S phase of interphase. Around 30 to 40 percent of cell cycle time is spent in the G<sub>1</sub> phase.
Overview
thumb|250px|Schematic [[karyogram of the human chromosomes, showing their usual state in the G<sub>0</sub> and G<sub>1</sub> phase of the cell cycle. At top center it also shows the chromosome 3 pair in metaphase (annotated as "Meta."), which takes place after having undergone DNA synthesis which occurs in the S phase (annotated as S) of the cell cycle.<br>]]
G<sub>1</sub> phase together with the S phase and G<sub>2</sub> phase comprise the long growth period of the cell cycle cell division called interphase that takes place before cell division in mitosis (M phase).
During G<sub>1</sub> phase, the cell grows in size and synthesizes mRNA and protein 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 G<sub>1</sub> phase, is different in many different types of cells. In human somatic cells, the G<sub>1</sub> stage of the cell cycle lasts about 10 hours. However, in Xenopus embryos, sea urchin embryos, and Drosophila embryos, the G<sub>1</sub> phase is barely existent and is defined as the gap, if one exists, between the end of mitosis and the S phase.
This point also separates two halves of the G<sub>1</sub> phase; the post-mitotic and pre-mitotic phases. Between the beginning of the G<sub>1</sub> phase (which is also after mitosis has occurred) and R, the cell is known as being in the G<sub>1</sub>-pm subphase, or the post-mitotic phase. After R and before S, the cell is known as being in G<sub>1</sub>-ps, or the pre S phase interval of the G<sub>1</sub> phase.
In order for the cell to continue through the G<sub>1</sub>-pm, there must be a high amount of growth factors and a steady rate of protein synthesis, otherwise the cell will move into G<sub>0</sub> phase. and skin cancers have been prevented from proliferating by causing the tumor cells to enter G<sub>1</sub> cell cycle arrest, preventing the cells from dividing and spreading.
See also
- G<sub>1</sub>/S transition