Question

Knowing what you know about the cell membrane, which signal molecules would you expect to rely on cell surface receptor proteins to initiate intracellular signaling?

(a) small and hydrophobic
(b) large and hydrophilic

Answer 1

Large and hydrophilic signal molecules need cell surface receptors to initiate intracellular signaling as they cannot diffuse through the cell membrane, whereas small and hydrophobic molecules can directly interact with intracellular receptors.

Step-by-step explanation:

Based on our knowledge of the cell membrane and its interactions with different types of signal molecules, we would expect large and hydrophilic signal molecules to rely on cell surface receptor proteins to initiate intracellular signaling. Cell-surface receptors are required for these molecules because they cannot diffuse through the lipid bilayer of the cell membrane due to their size and polarity. In contrast, small and hydrophobic signal molecules can typically diffuse across the plasma membrane and interact with intracellular receptors. An example of a small hydrophobic signal molecule is a steroid hormone, which is lipophilic and can easily cross the membrane to interact with internal receptors within the cell.