Common cell signaling pathway

Summary

Cells communicate through chemical signals that target nearby, distant, or even the same cells. These signals can be hydrophobic, passing through cell membranes, or hydrophilic, needing surface receptors. Signaling involves three stages: reception, transduction, and response. There are three main receptor types: G-protein coupled receptors, which activate intracellular pathways; enzyme-coupled receptors, which use protein kinases to relay signals; and ion channel receptors, which open to allow ions into cells. This complex system enables multicellular organisms to coordinate responses like hormone release or immune reactions.

Takeaways

• 🔗 Cells communicate via chemical signals that act on receptors of other cells.
• 🔁 Autocrine signals are self-targeted, meaning the cell sends a signal to itself.
• 🌍 Paracrine signals target nearby cells, while endocrine signals target distant cells through the bloodstream.
• 💧 Hydrophobic signaling molecules use carrier proteins and can diffuse across the cell membrane, binding to internal receptors.
• 💦 Hydrophilic molecules stay in extracellular space and bind to transmembrane receptors as they cannot cross the cell membrane.
• 🔑 Cell signaling has three stages: reception (ligand binds to receptor), transduction (activating second messengers), and response.
• 🧬 G protein-coupled receptors (GPCRs) have seven membrane-spanning segments and activate G proteins to transmit signals.
• 🌸 G proteins, composed of alpha, beta, and gamma subunits, activate other proteins when bound to GTP, triggering various pathways.
• ⚙️ Enzyme-coupled receptors activate intracellular enzyme activity when a ligand binds, often involving protein phosphorylation.
• 🔌 Ion channel receptors open when bound to specific ligands, allowing ions to pass and triggering cellular responses.

Q & A

What are the three types of cell signaling based on the distance between the signaling and target cells?

The three types of signaling are autocrine, paracrine, and endocrine. Autocrine signals target the same cell that produced them, paracrine signals act on nearby cells, and endocrine signals target distant cells through the bloodstream.

How do hydrophobic and hydrophilic signaling molecules differ in terms of movement across the cell membrane?

Hydrophobic signaling molecules can diffuse across the cell membrane and bind to intracellular receptors, but they need carrier proteins to move through the extracellular space. Hydrophilic signaling molecules can move freely in the extracellular space but cannot cross the membrane, so they bind to surface receptors.

What are the three stages of cell signaling?

The three stages of cell signaling are reception, where a ligand binds to a receptor; transduction, where the receptor changes shape and activates second messengers; and response, where the cell takes action based on the signal.

How does a G-protein coupled receptor activate G proteins?

When a ligand binds to the G-protein coupled receptor, the receptor changes shape, causing the G protein to release GDP and bind GTP, activating the G protein. The alpha subunit separates from the beta and gamma subunits and interacts with other proteins to relay the signal.

What are the three types of G proteins and what pathways do they affect?

The three types of G proteins are Gq, Gi, and Gs. Gq activates phospholipase C, Gi inhibits adenylate cyclase, and Gs stimulates adenylate cyclase to produce cAMP, which activates protein kinase A.

What is the function of phospholipase C in the Gq pathway?

Phospholipase C cleaves phosphatidylinositol 4,5-bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 triggers the release of calcium from the endoplasmic reticulum, and DAG activates protein kinase C.

How does cAMP activate protein kinase A?

cAMP binds to the regulatory subunit of protein kinase A, causing it to dissociate from the catalytic subunit. The catalytic subunit is then free to phosphorylate target proteins, triggering a cellular response.

What distinguishes enzyme-coupled receptors from G-protein coupled receptors?

Enzyme-coupled receptors have intrinsic enzyme activity or are associated with cytoplasmic enzymes. They are usually single-pass transmembrane proteins that phosphorylate target proteins directly, whereas G-protein coupled receptors rely on G proteins to relay the signal.

What happens when receptor tyrosine kinases bind to a ligand?

Receptor tyrosine kinases dimerize when they bind to a ligand, and they cross-phosphorylate each other at tyrosine residues. This creates binding sites for second messengers, which further propagate the signaling pathway.

How do ion channel receptors work in cell signaling?

Ion channel receptors remain closed until they bind a specific ligand. Once bound, the channel opens, allowing ions like sodium, potassium, or calcium to flow through, changing the electrical charge of the cell and triggering a cellular response.