Question

A scientist discovers a new hormone that is relatively large in size and that triggers the conversion of ATP to cAMP. Which of the following best describes the type of hormone that was just discovered? A. Amino acid-derived hormone B. Peptide hormone C. Steroid hormone D. Tropic hormone

Short answer

B. Peptide hormone

Step-by-step solution

Understand Hormone Types

First, review the different types of hormones: Amino acid-derived hormones are made from one or two modified amino acids. Peptide hormones are made of more than one amino acid (polypeptides). Steroid hormones are lipid-based and derived from cholesterol. Tropic hormones are hormones that stimulate other glands to release hormones.

Identify the Hormone's Characteristics

The hormone described in the exercise is noted to be relatively large in size and triggers the conversion of ATP to cAMP. Large size indicates it is a macromolecule and the conversion of ATP to cAMP suggests it interacts with cell surface receptors, since cAMP is a secondary messenger.

Match Characteristics with Hormone Types

Amino acid-derived hormones are typically small molecules, which do not fit the description of being 'large.' Steroid hormones are not likely to trigger large secondary messenger cascades like cAMP due to their mode of action (intracellular receptor binding). Tropic hormones describe function rather than structure; they can be any size or type.

Conclusion Based on Analysis

The peptide hormone typically fits the description of being large and acting via cell surface receptors triggering secondary messenger systems including cAMP.

Key concepts

Peptide Hormones

Peptide hormones are chains of amino acids that vary in length. They can be relatively short, with just a few amino acids, or much longer and more complex. These hormones generally cannot pass through the cell membrane due to their size and polar nature. Instead, they bind to receptors on the surface of the target cell.
Peptide hormones play crucial roles in various physiological processes, including metabolism, growth, and immune function. Examples include insulin, glucagon, and growth hormone.
When a peptide hormone binds to its receptor, it often triggers the activation of secondary messenger systems within the cell. This leads to a series of biochemical changes that produce the hormone's intended effect.

Secondary Messenger Systems

Secondary messenger systems act as an intermediary for the effects of hormones that cannot enter the cell. When a hormone binds to its receptor on the cell surface, it activates an enzyme or a receptor enzyme complex.
This activation results in the production of a secondary messenger inside the cell. For instance, when a peptide hormone binds to its receptor, it may trigger the conversion of ATP to cAMP (cyclic AMP), a common secondary messenger.
Secondary messengers have several roles:

• Amplifying the signal: A single hormone molecule can generate many secondary messenger molecules, thereby amplifying the effect.
• Producing diverse responses: Different secondary messengers can activate various signaling pathways within the cell.

Ultimately, these messengers translate the extracellular hormone signal into a specific intracellular action.

Hormone-Receptor Interactions

Hormone-receptor interactions are crucial for the specificity and efficiency of hormonal signaling. Each hormone binds to a specific receptor that is usually located on the surface of the target cell.
For peptide hormones, the receptor is typically a transmembrane protein. When the hormone binds to this receptor, it causes a conformational change in the receptor, activating it.
The activated receptor then initiates a signaling cascade inside the cell, often involving secondary messengers like cAMP. This interaction ensures that the hormone's signal is accurately relayed and amplified within the cell.
Some key features of these interactions include:

• Specificity: Each hormone will only bind to its unique receptor.
• Sensitivity: The receptors can detect even tiny amounts of the hormone.
• Reversibility: Hormone-receptor binding is reversible, allowing for regulation and fine-tuning of the response.

Biochemical Pathways

Biochemical pathways refer to the series of chemical reactions that occur within a cell in response to hormonal signals. When a peptide hormone binds to its receptor, it typically activates a secondary messenger system, which in turn activates other proteins and enzymes.
These biochemical pathways ensure that the hormone's message is carried out efficiently, leading to the desired cellular response.
An example of a biochemical pathway involves the activation of G-proteins and adenylate cyclase in response to cAMP production, leading to the activation of protein kinases that phosphorylate various cellular proteins.
Key elements of biochemical pathways:

• Enzyme cascades: A series of enzymes activate each other in a domino effect, leading to a rapid and amplified response.
• Feedback mechanisms: Biochemical pathways often include negative feedback loops that help maintain homeostasis.
• Integration: Multiple pathways can interact with each other, integrating various signals to produce a coordinated response.

Understanding these pathways is essential for grasping how hormones regulate complex physiological processes.