Which of the following is NOT a type of receptor mentioned?

• A. Channel-linked receptors
• B. Enzyme-linked receptors
• C. G protein-linked receptors
• D. Signal transduction receptors

Answer: (D)

The correct answer is based on the classification of receptors in cellular signaling systems. Channel-linked receptors, enzyme-linked receptors, and G protein-linked receptors are all well-defined categories of receptors that play crucial roles in signal transduction.

Channel-linked receptors, also known as ionotropic receptors, form ion channels that open in response to the binding of a ligand, allowing specific ions to flow across the cell membrane, which directly influences cellular activity.

Enzyme-linked receptors, or catalytic receptors, possess intrinsic enzymatic activity or are associated with enzymes that become activated upon binding with a ligand. This activation typically triggers a cascade of biochemical reactions within the cell, facilitating a response to a signal.

G protein-linked receptors, or metabotropic receptors, interact with G proteins to initiate a signaling cascade. Upon ligand binding, these receptors change conformation and activate the associated G protein, which then influences other intracellular signaling pathways.

In contrast, the term "signal transduction receptors" is not a specific type of receptor. Instead, it broadly refers to the overall process by which cells convert external signals into internal responses. This does not classify as a distinct category of receptor but rather describes the function that various receptors fulfill in the context of cellular communication.

Thus, "signal transduction receptors"