In many cases of local signaling messenger molecules are secreted by a

In many cases of local signaling messenger molecules

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In many cases of local signaling, messenger molecules are secreted by a signaling cellLocal regulators – messenger molecules that travel only short distancesOne class of these, growth factors, stimulates nearby cells to grow and divideParacrine signaling – numerous cells can simultaneously receive and respond to molecules of growth factor produced by a nearby cellSynaptic signaling – animal nervous systemSynaptic signaling consists of an electrical signal moving along a nerve cell and triggers the secretion of neurotransmitter molecules carrying a chemical signaloThese molecules can diffuse across the synapse (narrow space between the nerve cell and its target), triggering a response in the target cellIn long distance signaling, plants and animals use chemicals called hormonesHormonal signaling in animals (endocrine signaling) specialized cells release hormone molecules that travel via the circulatory systemoWhere they reach target cells that can recognize and respond to the hormonesMost plant hormones reach distant targets via plant vascular tissuesoXylem or phloemBut some travel through the air as a gasHormones vary in molecular size and type, as do local regulatorsoPlant hormone ethylene, a gas that promotes fruit ripening, is a hydrocarbon of only six atoms (C2H4)oMammalian hormone insulin, regulates sugar levels in the blood, is a protein with thousands of atomsTransmission of an electrical signal along the length of a single nerve cell can also be long-distance signalingoBc nerve cells can be pretty longJumping cell to cell via synapses, a nerve signal can quickly travel great distancesThe Three Stages of Cell Signaling: A Preview
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Earl W. Sutherland – investigated how the animal hormone epinephrine (adrenaline) stimulates the breakdown of storage polysaccharide glycogen within liver cells and skeletal muscle cellsoThis breakdown yields glucose molecules for the bodySutherland discovered that epinephrine never actually enters glycogen containing cells, which provided two insightsoEpinephrine doesn’t interact directly with the enzyme responsible for glycogen breakdown; an intermediate step or series of steps must be occurring inside the celloPlasma membrane must somehow be involved in transmitting the signalReception(1) – target cell’s detection of a signaling molecule coming from outside the cell, chemical signal is detected when the signaling molecule binds to a receptor protein located at the cells surface, or inside the cellTransduction(2) – step or series of steps that converts the signal to a form that can bring about a specific cellular responseoSignal transduction pathway – sequence of changes in a series of different moleculesRelay molecules – molecules in the pathwayResponse(3) – may be almost any imaginable cell activity, rearrangement of the cytoskeleton, or activation of specific genes in the nucleus
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