Which of the following is an ionophore?
**Core Concept**
Ionophores are a class of compounds that facilitate the transport of ions across biological membranes, often by forming complexes with the ions and allowing them to pass through the lipid bilayer. This property is crucial in various biological processes, including the regulation of cellular ion homeostasis and the functioning of ion channels.
**Why the Correct Answer is Right**
The correct answer is valinomycin, a peptide antibiotic that acts as an ionophore by selectively transporting potassium ions (K+) across cell membranes. This is achieved through a process called ion-channel formation, where valinomycin binds to potassium ions and forms a complex that allows them to pass through the lipid bilayer. Valinomycin's ability to selectively transport potassium ions makes it a useful tool in research and medicine, particularly in the study of cellular ion homeostasis and the treatment of certain diseases.
**Why Each Wrong Option is Incorrect**
**Option A:** Monensin is another ionophore, but it selectively transports sodium ions (Na+), not potassium ions. Therefore, it is not the correct answer.
**Option B:** Tetracycline is an antibiotic that inhibits protein synthesis, but it is not an ionophore.
**Option C:** Griseofulvin is an antifungal medication that interferes with microtubule function, but it is not an ionophore.
**Clinical Pearl / High-Yield Fact**
Ionophores like valinomycin can be used to study the role of potassium ions in various cellular processes, including muscle contraction and nerve function.
**Correct Answer: C. Valinomycin**