Which of these receptors is not a membrane receptor?

• A. Ion channel receptor
• B. G-protein coupled receptor
• C. Enzyme-linked receptor
• D. Nuclear receptor

Answer: (D)

Verified step by step guidance

1. Understand the types of receptors: Receptors are proteins that receive and respond to chemical signals. They can be located on the cell membrane or inside the cell.
2. Identify membrane receptors: Membrane receptors are located on the cell surface and include ion channel receptors, G-protein coupled receptors, and enzyme-linked receptors. These receptors interact with extracellular molecules and transmit signals into the cell.
3. Define ion channel receptors: Ion channel receptors are membrane proteins that open or close in response to a ligand binding, allowing ions to pass through the membrane.
4. Define G-protein coupled receptors: G-protein coupled receptors are a large family of membrane receptors that activate G-proteins when a ligand binds, leading to various intracellular responses.
5. Define enzyme-linked receptors: Enzyme-linked receptors are membrane receptors that have an enzymatic activity or are associated with enzymes, and they initiate a signaling cascade upon ligand binding.
6. Clarify nuclear receptors: Nuclear receptors are not membrane receptors. They are located inside the cell, often in the cytoplasm or nucleus, and they bind to ligands that can cross the cell membrane, such as steroid hormones, to regulate gene expression.