For each of the following sentences, fill in the blanks with the best word or ph

Question

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. The survival, , and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface and trigger various intracellular signaling pathways. One class of signal molecules, called , stimulates cell division by releasing the molecular brakes that keep cells in the or phase of the cell cycle. Members of a second class of signal molecules are called , because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called , inhibits by regulating members of the family of proteins. In addition to such stimulatory factors, some signal proteins such as act negatively on other cells, inhibiting their survival, growth, or proliferation.

Explanation / Answer

The survival, proliferation, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface receptor and trigger various intracellular signaling pathways. One class of signal molecules, called mitogens, stimulates cell division by releasing the molecular brakes that keep cells in the G0 or G1 phase of the cell cycle. Members of a second class of signal molecules are called growth factors, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called survival factors, inhibits apoptosis by regulating members of the Bcl2family of proteins. In addition to such stimulatory factors, some signal proteins such as myostatin act negatively on other cells, inhibiting their survival, growth, or proliferation.

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