Question

What are the differences between internal receptors and cell-surface receptors?

a) Internal receptors bind to extracellular ligands, while cell-surface receptors bind to intracellular ligands
b) Internal receptors are membrane-bound, while cell-surface receptors are located in the cytoplasm
c) Internal receptors are activated by second messengers, while cell-surface receptors directly activate gene expression
d) Internal receptors respond to lipid-soluble ligands, while cell-surface receptors respond to water-soluble ligands

Answer 1

The key difference is that internal receptors interact with lipid-soluble ligands and directly influence gene expression, while cell-surface receptors bind water-soluble ligands and transmit signals into the cell through various pathways.

Step-by-step explanation:

The differences between internal receptors and cell-surface receptors pertain to their location, the types of ligands they bind, and how they mediate cellular responses. Internal receptors are found within the cell, typically in the cytoplasm or nucleus, and they respond to lipid-soluble ligands. These ligands are able to cross the cell membrane and interact with the receptors to initiate direct gene expression. On the other hand, cell-surface receptors are transmembrane proteins that respond to water-soluble ligands, which cannot pass through the cell membrane. These receptors initiate signal transduction pathways to convey the message into the cell's interior.

Given the options provided, the correct answer is (d): Internal receptors respond to lipid-soluble ligands, while cell-surface receptors respond to water-soluble ligands.