question 73 | how do cells talk to each other?

answer 73 | cellular conversations are felt, not heard.

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information flows from one cell to another through
/ cell signaling pathways \
that require signals, receptors and responders.

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As a signal is passed between one cell and another, it is received by a receptor located on the cell membrane.

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This triggers the responder to secrete new signals,
change cell shape or movement, or even

die.

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Surprisingly, there are only 17 major cell signaling pathways in animals.

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These same pathways somehow choreograph all the different ways embryos develop into distinct species with diverse body types.

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Furthermore,

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cell signaling pathways work similarly in plants, fungi, and even in unicellular organisms. How the same means can work to achieve such different ends remains mysterious.

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Three contested properties could help resolve the paradox. First:

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the same signaling pathway often elicits totally different responses depending on the strength of the signal.
Second,

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responders might be able to read combinatorial codes written by two or more co-stimulated receptors.
Finally,

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crosstalk between signaling pathways could fine-tune responses.

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For instance,

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some signals degrade signals
from other pathways

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– literally eating their words.

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answer 73, part ii | feeling is hearing.

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