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Which of the following is likely to be a response by a receptor protein to an approaching signal molecule?
a) The receptor protein binds to the signal if it has a complementary shape.
b) If the signal is able to bind to the receptor it induces a change in the receptor protein's shape.
c) The change in the receptor protein's shape results in cellular action.
d) All of the above are correct.
Signal transduction pathways:
a) Are necessary for signals to cross the membrane.
b) Include the intracellular events caused by a signal binding to a receptor.
c) Include the extracellular events caused by a signal binding to a receptor.
d) Carry a signaling molecule to the nucleus of a cell.
What does it mean to say that a signal is transduced?
a) The signal enters the cell directly and binds to a receptor inside.
b) The physical form of the signal changes as it passes from the cell membrane to the intracellular target.
c) The signal is amplified, such that even one signal molecule evokes a large response.
d) The signal triggers a sequence of phosphorylation events inside the cell.
Why does testosterone, a lipid-soluble / hydrophobic signaling molecule, not affect all cells in the body but only specific cells?
a) Only target cells have the cell surface receptor able to bind with testosterone.
b) Only target cells contain the genes regulated by testosterone.
c) Only target cells possess the phosphorylation cascade uniquely activated by testosterone.
d) Only target cells possess the intracellular receptor able to bind with testosterone.
Kinases and phosphatases are essential to the cell because they:
a) Are enzymes that synthesize proteins.
b) Are enzymes that degrade proteins.
c) Are enzymes that can turn proteins “on” and/or “off” through changes in phosphorylation.
d) Are enzymes that can turn proteins “on” and/or “off” through changes in proton concentrations.
e) None of the above.
What role do phosphatases play in signal transduction pathways?
a) They phosphorylate proteins involved in signal transduction or cellular response.
b) They activate protein kinases by phosphorylation.
c) They amplify the signal molecule.
d) They regulate the function of proteins involved in signal transduction pathways or cellular response.
Phosphorylation cascades are useful signal transduction pathways because they ________.
a) Allow proteins to be easily activated by adding or removing a phosphate group.
b) Allow proteins to be easily deactivated by adding or removing a phosphate group.
c) Amplify the original signal many times.
d) All of the above.
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