Question

In the interaction of a hormone with irs receptor, all of the following are true except A. more than one polypeptide chain of the hormone may be necessary. B. more than one second messenger may be generated. C. an array of transmembrane helices may form the binding site for the hormone. D. receptors have a greater affinity for hormones than for synthetic agonists or antagonists. E. hormones released from their receptor after endocytosis could theoretically interact with a nuclear receptor.

Short answer

Answer: E. hormones released from their receptor after endocytosis could theoretically interact with a nuclear receptor.

Step-by-step solution

Statement A: More than one polypeptide chain of the hormone may be necessary.

This statement is true. In some cases, hormones can be composed of two or more polypeptide chains, which are necessary for the hormone to function and interact with its receptor properly.

Statement B: More than one second messenger may be generated.

This statement is also true. During hormone-receptor interaction, it is possible for the activated receptor to generate and/or interact with multiple second messengers, which help to amplify and propagate the signal throughout the cell.

Statement C: An array of transmembrane helices may form the binding site for the hormone.

This statement is true. Hormone receptors can be embedded within the cell membrane and can consist of several transmembrane helices that together form the binding site for the hormone. This structure allows the hormone to bind to the receptor and initiate a cellular response.

Statement D: Receptors have a greater affinity for hormones than for synthetic agonists or antagonists.

This statement is generally true. Hormone receptors typically have a higher affinity for their natural hormone ligands than for synthetic agonists or antagonists. This ensures that the hormone can effectively bind to its receptor and initiate the necessary cellular response. synthetic agonists or antagonists are usually designed to mimic or block the action of natural hormones, so they typically have a lower affinity for the receptor than the hormone itself.

Statement E: Hormones released from their receptor after endocytosis could theoretically interact with a nuclear receptor.

This statement is the exception and is not true. Once a hormone is internalized with its receptor through endocytosis, it is typically degraded within the cell and does not interact with nuclear receptors. Nuclear receptors are activated by small, lipophilic molecules that can easily diffuse across the cell membrane; they do not interact with peptide hormones that have been internalized through endocytosis. So, the statement that is not true is: E. hormones released from their receptor after endocytosis could theoretically interact with a nuclear receptor.

Key concepts

Polypeptide Chains in Hormones

Imagine hormones as little messengers of the body, racing around to deliver important information from one part to another. Now, some of these messengers are quite complex; they are made up of polypeptide chains. Polypeptide chains are like strings of pearls, where each pearl is an amino acid, and different combinations can create various hormones with distinct functions. For instance, insulin, a hormone that helps regulate blood sugar levels, consists of two such chains linked together. The design of these chains is critical because it determines how the hormone will recognize and bind to its specific receptor.

It's like having the right key for the right lock; unless the shapes complement each other, the message won't be delivered. This matching is precisely why some hormones require more than one polypeptide chain - teamwork is necessary to create the right structure to unlock the receptor and elicit the cell's response.

Second Messenger Generation

Once a hormone docks onto its receptor like a ship to its port, it often triggers a cascade inside the cell. This series of events involves the creation of second messengers. These are molecules that carry the signal deeper into the cell, like relay runners passing a baton. The classic example might be cyclic adenosine monophosphate (cAMP), which is generated when hormones like adrenaline interact with their surface receptors.

Second messengers are essential because they can amplify the signal. Even if only a small number of hormone molecules bind to receptors, the creation of numerous second messengers can lead to a substantial cellular response. It's like flicking a switch that turns on a whole row of lights. This amplification ensures that the cell fully responds to the hormone's message, orchestrating tasks such as converting stored energy into a form that the cell can use immediately.

Transmembrane Helices

Transmembrane helices are like the skyscrapers of the cellular world, spanning the cell membrane and creating pathways for signals to travel in and out. In hormone receptors, these helices are arranged in a way that forms a docking station for the hormone—a binding site where the action begins. Typically, these receptors have several helices that thread back and forth through the membrane, stabilizing the structure and providing a specific shape for hormone attachment.

Therefore, these transmembrane helices are not just structural elements but are critical in recognizing and binding the hormone so that it can deliver its message effectively. Each helix can be thought of as part of a puzzle that, when assembled correctly, forms the big picture needed to transmit signals that regulate everything from growth to metabolism.

Affinity of Hormone Receptors

The affinity of hormone receptors is like the strength of a magnetic attraction between the hormone (the magnet) and the receptor (the metal surface). It's a measure of how well the hormone sticks to its receptor and initiates a cellular response. Generally, hormone receptors have a higher affinity for the hormones they are meant to bind with, which means they prefer the natural hormones over other substances, such as synthetic drugs.

Just as some magnets are stronger than others, different receptors have different affinities for their corresponding hormones. This selectivity ensures precise control—like a dial regulating how much signal gets through based on how tightly the hormone binds. Synthetic agonists or antagonists are like weaker magnets designed to compete with natural hormones. They either mimic (agonist) or block (antagonist) the hormone's action but usually don't stick as well to the receptor. The high affinity of natural hormones ensures that our bodies respond more efficiently to internal cues rather than external substances.