Question

Hormones are found in the body in very low concentrations, but tend to have a strong effect. What type of receptor are hormones most likely to act on? Ligand-gated ion channels . Enzyme-linked receptors I. G protein-coupled receptors (A) I only (B) III only (C) II and III only (D) I, II, and III

Short answer

The correct answer is (C) II and III only.

Step-by-step solution

- Understand the Different Receptor Types

Ligand-gated ion channels are receptors that open to allow ions to pass through the membrane in response to the binding of a chemical messenger. Enzyme-linked receptors are receptors that, when activated, trigger an intracellular enzyme. G protein-coupled receptors (GPCRs) are a large family of receptors that activate intracellular signaling pathways and influence cellular responses.

- Analyze the Role of Hormones

Hormones typically operate in very low concentrations but need to produce strong and amplified effects in the body. Consider which type of receptor could fulfill this role given their described mechanism of action.

- Match Hormones with Receptor Types

Hormones are best suited to act on G protein-coupled receptors (GPCRs) because these receptors can amplify the signal through a cascade effect. While enzyme-linked receptors also play a role, ligand-gated ion channels are generally not used by hormones, as their role is more immediate and localized rather than broadly regulatory.

- Select the Correct Answer

Based on the analysis, hormones are likely to act on enzyme-linked receptors and G protein-coupled receptors. Therefore, the correct answer is (C) II and III only.

Key concepts

ligand-gated ion channels

Ligand-gated ion channels are specialized protein structures found in the cell membrane. They act like a gate that opens in response to the binding of a chemical messenger or ligand.
When a ligand binds to the extracellular side of the channel, it causes the protein to change shape and open, allowing specific ions to flow through the channel.
This change in ion concentration inside the cell can lead to various cellular responses, such as the initiation of an electrical signal in nerve cells.

• They provide a fast response
• Commonly involved in neurotransmission
• Not typically used by hormones

Ligand-gated ion channels are crucial for rapid, localized cellular communication, often seen in neurons and muscle cells. However, they are generally not employed by hormones, as hormone signaling tends to involve broader and more sustained effects.

enzyme-linked receptors

Enzyme-linked receptors are proteins that, when bound by a hormone or ligand on the extracellular side, activate an enzyme on the intracellular side of the membrane.
This enzyme then catalyzes reactions that alter cell function.

• Involve direct activation of intracellular enzymes
• Can initiate multiple signaling pathways
• Often involved in growth and development

One common type is the receptor tyrosine kinase, which phosphorylates target proteins upon activation.
This phosphorylation can trigger a variety of intracellular signaling cascades, leading to changes in gene expression, cell division, or metabolism. Enzyme-linked receptors are slower but facilitate significant changes in cell activity, making them suitable for hormonal effects.

g protein-coupled receptors

G protein-coupled receptors (GPCRs) form a large and diverse group of membrane receptors that interact with G proteins inside the cell.
Upon binding a hormone at the surface, a GPCR activates a G protein on the inside of the membrane, which then influences other intracellular signaling pathways and amplifies the signal.

• Trigger complex signaling cascades
• Can produce amplified effects
• Involved in many physiological processes

The GPCR family is well-suited to transmit signals from hormones that need to trigger widespread and amplified cellular responses.
Examples include adrenaline, which signals through GPCRs to elicit a strong fight-or-flight response throughout the body.

hormone signal amplification

Hormone signal amplification is the process by which a single hormone molecule can generate a large-scale cellular response. This is crucial because hormones are found in very low concentrations but need to exert significant effects to regulate body processes.
Both GPCRs and enzyme-linked receptors can achieve amplification.

• GPCRs activate G proteins that trigger numerous downstream signals
• Enzyme-linked receptors often activate kinase cascades
• Allows small hormone amounts to produce sizable impacts

The amplification ensures that even a tiny amount of hormone can bring about a substantial physiological response, which is essential for the tight regulation of bodily functions such as metabolism, growth, and stress responses.