Chapter 8: Cell Communication

Cell Communication

The process by which cells detect and respond to signals in their environment.

Direct intercellular signaling

Cell junctions allow signals to pass directly from one cell to another

Contact-dependent signaling

Molecules bound to the surface of cells serve as signals to other cells encountering them in close proximity.

Autocrine signaling

Cells secrete signaling molecules that bind to their own surface receptors or neighboring cells to induce a response.

Paracrine signaling

Cells release signals that affect nearby cells

Endocrine signaling

Signals (hormones) are released into the blood and affect target cells far away

Three stage process of Cell Signaling

Receptor activation, signal transduction, cellular response

Receptor Activation

A signaling molecule (ligand) binds to a receptor, causing a conformational change that transmits the signal.

Ligand

A signaling molecule that binds noncovalently to a receptor with high specificity.

Dissociation Constant (Kd)

A measure of the affinity between a receptor and its ligand; it is inversely related to the affinity, with lower Kd values indicating higher affinity.

Cell Surface Receptors

Proteins located on the cell membrane that detect extracellular signals (ex: small & hydrophilic or too large to pass through the plasma membrane)

Three types of receptors

Enzyme-linked receptors, G-protein-couples receptors, ligand-gated ion channels

• all responds to different signals

Enzyme-Linked Receptors

Cell surface receptors with an extracellular signal-binding domain and an intracellular catalytic domain, often functioning as protein kinases.

G-Protein-Coupled Receptors (GPCRs)

Cell surface receptors that interact with intracellular G proteins, which bind GTP and GDP and dissociate into subunits upon receptor activation.

Ligand-Gated Ion Channels

Cell surface receptors that open an ion channel upon binding a signaling molecule, allowing ions to flow across the membrane.

Intracellular Receptors

Receptors located in the cytosol or nucleus that bind small, hydrophobic signal molecules that can diffuse across the plasma membrane, often