Biology – Fluid mosaic membranes | e-Consult

Receptor diversity is essential for the complexity and adaptability of cell signalling. Different cells express different combinations of receptors, allowing them to respond to a wide range of signals. This diversity is crucial for coordinating cellular responses in different tissues and organs. Here's a breakdown:

Types of Receptors and Signals They Respond To:

• G protein-coupled receptors (GPCRs): These are the largest family of cell surface receptors. They respond to a vast array of ligands, including hormones (e.g., adrenaline, insulin), neurotransmitters (e.g., dopamine, acetylcholine), and photons (e.g., rhodopsin). Upon ligand binding, they activate intracellular G proteins, which then modulate the activity of various enzymes and ion channels.
• Receptor tyrosine kinases (RTKs): These receptors are typically involved in cell growth, differentiation, and survival. They respond to growth factors (e.g., epidermal growth factor, platelet-derived growth factor). Ligand binding causes RTKs to dimerize and become phosphorylated, creating docking sites for intracellular signalling proteins.
• Ion channel receptors: These receptors directly form ion channels that are gated by ligand binding. Examples include nicotinic acetylcholine receptors (which open when acetylcholine binds) and GABA receptors (which open when GABA binds). These receptors mediate rapid changes in membrane potential.
• Ligand-gated ion channels: These receptors open ion channels upon ligand binding, leading to changes in membrane potential. Examples include neurotransmitter receptors at synapses.
• Intracellular receptors: These receptors are located inside the cell (in the cytoplasm or nucleus) and bind to hydrophobic ligands (e.g., steroid hormones, thyroid hormones). The ligand-receptor complex then acts as a transcription factor, regulating gene expression.

How Diversity Allows for a Wide Range of Cellular Responses:

The diversity of receptors allows cells to respond to a wide range of signals, each triggering a different intracellular signalling pathway. This means that a single cell can be influenced by multiple signals, leading to complex and coordinated responses. For example, a cell might respond to a growth factor by activating a pathway that promotes cell growth and division, and simultaneously respond to a cytokine by activating a pathway that promotes inflammation. The specific combination of receptors expressed by a cell determines its responsiveness to different signals, allowing for highly specific and tailored cellular responses. This is fundamental to development, immunity, and homeostasis.