**Core Concept:** Receptors are specialized molecules on the surface of cells that can bind to specific molecules in the environment, such as hormones or neurotransmitters. When activated, these receptors initiate a cellular response. Changes in the chemical composition of the environment can stimulate different types of receptors.

**Why the Correct Answer is Right:** Option C, G protein coupled receptors (GPCRs), are activated by changes in the chemical environment. GPCRs are a large family of receptors that are involved in various physiological processes, including hormone signaling and neurotransmission. When these receptors bind to their respective ligands (hormones or neurotransmitters), they initiate intracellular signaling pathways that lead to cellular responses.

**Why Each Wrong Option is Incorrect:**

A. Transcription factor receptors (Option A) are activated by changes in the gene expression, not the chemical environment. They are involved in the process of gene activation or repression in response to specific signaling molecules.

B. Nucleotide-gated ion channels (Option B) are activated by changes in membrane potential, not the chemical environment. They are ion channels that open or close in response to the binding of nucleotides, such as ATP or ADP, to the channel.

D. Receptor tyrosine kinases (Option D) are activated by changes in receptor-ligand binding, not the chemical environment. They are a class of receptors that contain an intracellular tyrosine kinase domain and are involved in cell signaling processes such as cell growth, differentiation, and apoptosis.

**Clinical Pearl:** Understanding the various types of receptors and their activation mechanisms is essential for understanding cellular signaling pathways and their roles in physiological processes. This knowledge is crucial for medical students, residents, and practicing physicians alike in their understanding of diseases and treatments involving receptor activation, such as drug actions and side effects.

**Correct Answer:** C. G protein coupled receptors (GPCRs) are activated by changes in the chemical environment. GPCRs are involved in various physiological processes, including hormone signaling and neurotransmission. When GPCRs bind to their respective ligands (hormones or neurotransmitters), they initiate intracellular signaling pathways that lead to cellular responses.