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Different hormones have different roles in cell signaling. Identify the term for a hormone that initiates cell-signaling pathways.

a) Effector hormone
b) Signal molecule
c) First messenger
d) Downstream hormone

User Thertweck
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Final answer:

The correct term for a hormone that initiates cell-signaling pathways is c) First messenger. This hormone binds to cell surface receptors and sets off a signaling cascade within the cell, leading to various cellular responses.

Step-by-step explanation:

Among the options provided, the term for a hormone that initiates cell-signaling pathways is c) First messenger. This hormone is released in response to a stimulus and travels through the bloodstream to reach the target cells. Upon binding to hormone receptors on the cell surface, it triggers a series of events internally, without crossing the cell membrane. This is because hormones like amino acid-derived and polypeptide hormones are not lipid-soluble and bind to extracellular receptors, initiating a signaling cascade inside the cell. Such a hormone is known as a first messenger, which activates subsequent cellular changes through second messengers such as cAMP, enzymes, and other intracellular proteins, ultimately resulting in a cellular response.

In signal transduction, the events following the binding of the hormone are likened to a cascading river flow, with the events categorized as upstream (before activation) and downstream (after activation). The hormone, functioning as a first messenger, is fundamental in this process because it serves as the initial trigger for the signaling pathway.

User Matheus Frik
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