Cell growth can refer to an increase in cell number, by proliferation and cell division, or to an increase in the cells volume, without cell division. Growth of a cell population or cell doubling is dependent on cell division, and involves the completion of successive cell cycles. Cell growth in terms of volume, is when the cytoplasm and organelles of a cell increase in volume due to increased transcription and protein synthesis. This occurs during G1 and G2 phases of the cell cycle, in preparation of the cell prior to DNA duplication during S-phase, or prior to cell division into two daughter cells during the mitotic phase.
Certain secreted growth factors regulate cell growth by initiating cell signaling with subsequent activation of specific transcription factors. These transcription factors activate the expression of particular gene sets involved in cell cycle progression, to induce cells to enter the cell cycle and proliferate, or involved in promoting cellular growth in size. For instance, transcription factors of the E2F family control cell cycle progression by inducing the transcription of genes necessary for entry into the S-phase of the cell cycle.
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