Question

Two problems encountered with oral or intravenous administration of drugs are the lack of tissue specificity in the action of the drug and rapid metabolism, and therefore limited period of effectiveness, of some drugs. One attempt to circumvent these problems is the use of liposomes to encapsulate the drugs. Some drugs have a longer period of effectiveness when administered this way. Liposomes can be prepared with specific proteins to bind specific cellular membrane receptors. Liposomes are also useful as a research tool to study the properties of biological membranes since they have a similar structure and properties. Much of our understanding of biological membranes has been obtained using liposomes. Plasma membrane receptors A. usually have as ligands molecules like steroids. B. are always coupled to G-proteins. C. are fixed in number for a given cell. D. often span the membrane with one or more transmembrane domains. E. when bound to their ligand, always result in the release of a small molecule (second messenger) into the cell.

Short answer

Answer: D. often span the membrane with one or more transmembrane domains.

Step-by-step solution

Read about plasma membrane receptors

Before solving this exercise, make sure to have a clear understanding of plasma membrane receptors and their role in cellular communication.

Evaluate the given options

Let's analyze each of the given statements to check which one is correct regarding plasma membrane receptors: A. usually have as ligands molecules like steroids. While some plasma membrane receptors may interact with steroids, not all of them do. This statement is too broad and does not accurately describe all plasma membrane receptors. B. are always coupled to G-proteins. Only certain subsets of plasma membrane receptors are coupled to G-proteins, known as G-protein coupled receptors (GPCRs). Therefore, this statement is also inaccurate. C. are fixed in number for a given cell. The number of membrane receptors on a cell can vary depending on cellular signaling, cellular development, and other factors. This makes this statement incorrect. D. often span the membrane with one or more transmembrane domains. This statement is correct. Many plasma membrane receptors span the membrane with transmembrane domains. This allows them to facilitate communication between the extracellular and intracellular environments. E. when bound to their ligand, always result in the release of a small molecule (second messenger) into the cell. Not all plasma membrane receptors generate a second messenger upon binding to their ligands. Some receptors exhibit different behavior depending on the specific receptor-ligand interaction. This statement is inaccurate.

Identify the correct statement

Based on our analysis, we can conclude that the correct statement about plasma membrane receptors is: D. often span the membrane with one or more transmembrane domains.