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Signal Transduction by Extracellular Receptors

How has extracellular signaling evolved? Cells have a wide variety of molecular pathways for transmitting information from one cell to another. However many different pathways have very similar mechanisms for converting the information from an external messenger molecule to an internal signaling pathway. The mechanism for converting the external signal to an internal pathway is called signal transduction. The implication is that signal transduction evolved a few times and that the relatively small number of basic mechanisms for transduction have been used for a large number of different extracellular signals.

View the animation below, then complete the quiz to test your knowledge of the concept.






1Ion channels...
A)open when a first messenger binds to a membrane receptor protein / tyrosine kinase complex, which opens the ion channel and prompts the cell response.
B)open when a first messenger binds to a membrane receptor protein / G protein complex, which opens the ion channel and prompts the cell response.
C)open when a first messenger binds to a membrane receptor protein, which opens the ion channel and prompts the cell response.
D)open when a first messenger binds to a membrane receptor protein / JAK kinase, which opens the ion channel and prompts the cell response.
E)open when a first messenger binds to a membrane receptor protein / docking protein complex, which opens the ion channel and prompts the cell response.



2The function of a docking protein is...
A)to bind to the first messenger / receptor protein complex which activates an effector protein which initiates multiple steps leading to a cell response.
B)to bind with the JAK kinase / receptor protein / first messenger complex, which then binds to the phosphate from an ATP molecule, and initiates multiple steps leading to a cell response.
C)to bind to the first messenger / receptor protein complex which opens an ion channel and promotes the cell response.
D)to bind to a phosphate from ATP and the tyrosine kinase / receptor protein / first messenger complex to initiate multiple steps leading to a cell response.
E)to bind with a G protein which activates an effector protein which initiates multiple steps leading to a cell response.



3The function of a G protein is...
A)to bind to the first messenger / receptor protein complex which opens an ion channel and promotes the cell response.
B)to relay a signal from the first messenger / receptor protein complex to activate an effector protein in the cell membrane which leads to multiple steps which produce a cell response.
C)to bind to a phosphate from ATP and the tyrosine kinase / receptor protein / first messenger complex to initiate multiple steps leading to a cell response.
D)to generate a change in membrane potential or a second messenger system which promotes the cell response.
E)to bind with the JAK kinase, which then initiates multiple steps leading to a cell response.



4First messengers are by definition hydrophobic.
A)True
B)False



5The common thread for signal transduction by extra cellular receptors is that a first messenger is unable to pass through the cell membrane, and therefore must activate a membrane receptor protein to initiate an intracellular response.
A)True
B)False







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