Question

How can two different molecules fit the same receptor, yet only one of the two activates the signal transduction pathway?

a) The receptor's shape allows multiple molecules to bind.
b) Both molecules have identical chemical structures.
c) The receptor is specific to only one molecule.
d) Molecular size determines receptor activation.

Answer 1

Ligand binding to a receptor causes conformational changes which can lead to dimerization and activation of the receptor's intracellular domain.

Step-by-step explanation:

When a ligand binds to its receptor, conformational changes occur that affect the receptor's intracellular domain. These conformational changes lead to activation of the intracellular domain or its associated proteins. In some cases, binding of the ligand causes dimerization of the receptor, which means that two receptors bind to each other to form a stable complex called a dimer. A dimer is a chemical compound formed when two molecules (often identical) join together. The binding of the receptors in this manner enables their intracellular domains to come into close contact and activate each other.

Answer 2

Receptors can bind multiple molecules, but only specific activating ligands induce the conformational changes necessary to trigger signal transduction pathways. This specificity is based on the molecule's ability to change the receptor's shape in a way that activates the intracellular signaling domain.

Step-by-step explanation:

The question explores how two different molecules can fit the same receptor, yet only one of the two activates the signal transduction pathway. This phenomenon can occur because a receptor's shape allows multiple molecules to bind, but only certain molecules induce the appropriate conformational changes that trigger downstream signaling. While numerous signaling molecules can interact with the extracellular domain of a receptor, the specific geometric and chemical properties of the activating ligand cause a conformational shift in the receptor that propagates through to the intracellular domain, leading to the activation of signaling cascades within the cell. In contrast, a non-activating ligand might bind to the receptor but not induce the necessary conformational changes for signaling to occur.

Cell signaling pathways begin with ligand-receptor interaction. Receptors on cell surfaces or within the cell can be highly specific, recognizing and binding to precise ligands. Polar ligands often interact with membrane receptor proteins, inducing a variety of responses such as ion channel opening or G-protein activation, while nonpolar ligands diffuse across the cell membrane and bind to internal receptors, influencing gene expression by interacting with DNA in the nucleus.