The three stages of cell signaling are reception, transduction, and response. What happens when a cell encounters a signal? The signal must be recognized by a specific receptor molecule, and the information it carries (the signal) must be changed into another form, or transduced, inside the cell, before the cell can respond. E. W. Sutherland and his colleagues pioneered our understanding of cell signaling by investigating how the animal hormone epinephrine stimulates the breakdown of the storage polysaccharide glycogen in liver and skeletal muscle cells. o The breakdown of glycogen releases glucose derivatives that can be used for fuel in glycolysis or released as glucose in the blood for fuel elsewhere. o Thus, one effect of epinephrine, which is released from the adrenal gland during times of physical or mental stress, is mobilization of fuel reserves. Sutherland’s research team discovered that epinephrine stimulates glycogen breakdown by
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