Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?

The molecules that convert extracellular signals into intracellular signals are:

a) Neurotransmitters.

b) Hormones.

c) Cell surface receptors.

d) Intracellular receptors.

Which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

a) Receptor tyrosine kinase.

b) G protein-coupled receptor.

c) Ligand-gated ion channel.

d) Steroid receptor.

e) Intracellular receptor.

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.