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Example Questions
Example Question #1 : Understand Types Of Signaling, Receptors, And Signaling Molecules
Which type of ligand is water soluble, and thus unable to enter a cell?
Possible Answers:
steroid hormones
Nitric oxide
Small, hydrophobic ligands
Water-soluble ligands
Correct answer:
Water-soluble ligands
Explanation:
The membrane of the cell is a phospholipid bilayer, which allows hydrophobic molecules to diffuse through it. Small, hydrophobic ligands are able to diffuse through the plasma membrane. Nitric oxide is lipophilic, readily dissolving in lipids, and can diffuse across the plasma membrane. Steroid hormones are hydrophobic, and can thus diffuse across the plasma membrane. Water-soluble ligands cannot diffuse across the plasma membrane to enter a cell.
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