Density-independent factors limit population size regardless of the population’s density.

Common density-independent factors include natural disasters such as tornadoes, hurricanes, floods, and fires.

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GPCRs specifically activate the β isoform of PLC (PLCβ)

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Many RTKs and cytokine receptors specifically activate the γ isoform (PLCγ), which contains an SH2 domain.

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Activated RTKs and cytokine receptors promote PLCγ activity in two ways: 

By localizing PLCγ to the membrane

By phosphorylating PLCγ

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The SH2 domains of PLCγ bind to specific phosphotyrosines on the activated RTKs and cytokine receptors, thus positioning PLCγ close to PIP2.

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Kinase activity associated with receptor activation phosphorylates tyrosines on the bound PLCγ, enhancing its hydrolase activity. 

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Activated RTKs and cytokine receptors initiate another phosphoinositide pathway by recruiting PI-3 kinase to the cytosolic surface of the plasma membrane.