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  • Signaling Cell: A cell that produces and releases signal molecules.

  • Responding Cell: Detects and responds to signaling molecules (small water-soluble) (Target Cell).

  • Receptor Activation: Process of receptor binding to a signal molecule and initiating a cellular response.

  • Endocrine: Long-distance communication involving hormones traveling through the bloodstream.

  • Paracrine: Short distance (within 20 neighboring cells) via diffusion.

  • Autocrine: Cell signaling to itself by releasing molecules that bind to its own receptors.

  • Contact Dependent: Communication requiring direct cell-to-cell contact.

  • Nonpolar Signaling Molecule: Small and passes through cell membranes (hydrophobic core).

  • Polar Signaling Molecule: Doesn’t pass through but instead binds to transmembrane protein receptors.

  • Ligand (Signaling Molecule): A molecule that binds to a specific receptor to trigger a signal.

  • Receptor: Protein molecule that binds to a ligand to initiate signaling.

  • Ligand Binding Site: Region of the receptor binding to the signal molecule.

  • G Protein: Signaling protein activated by G-protein-coupled receptors that relays signals.

  • Phosphatase: Enzyme that removes phosphate groups from proteins, terminating signals.

  • Protein Kinase A (PKA): Enzyme activated by cAMP that phosphorylates other proteins.

  • Second Messenger: Small molecules like cAMP that relay signals inside the cell.

  • Cyclic AMP (cAMP): A second messenger involved in transmitting cellular signals.Signal Transduction: Process of transmitting a signal from a receptor to a response.

  • Signal Termination: When a signal is read and acted upon so other signals can be processed.

  • Binding Affinity: Strength of interaction between a ligand and a receptor.Principles of Cell Signaling: Cells communicate by binding, transduction, and response.

  • Short & Long-Distance Communication:

    • Short: Paracrine, Autocrine, Contact-dependent.

    • Long: Endocrine (through the bloodstream).

  • Signal Amplification: A process where a single signal molecule triggers a large-scale response in the cell.

  • G Protein-Coupled Receptors (GPCR): Receptors activated by G proteins; the largest class of membrane proteins.

  • Receptor Kinases: Enzymes that phosphorylate proteins upon activation by signal molecules.

  • Ligand-Gated Ion Channels: Ion channels that open and close in response to ligand binding, allowing ion flow across membranes for cell signaling.