Cell Communication Chapter 9

Overview Communication between cells requires these basic steps: sending, receiving, signal transducing, responding Ligand – signaling molecule Receptor protein – molecule to which the receptor binds Interaction of these two components initiates the process of signal transduction, which converts the information in the signal into a cellular response

There are four basic mechanisms for cellular communication Direct contact Paracrine signaling Endocrine signaling Synaptic signaling Some cells send signals to themselves (autocrine signaling)

Direct contact Molecules on the surface of one cell are recognized by receptors on the adjacent cell Important in early development Gap junctions

Paracrine signaling Signal released from a cell has an effect on neighboring cells Signaling between immune cells Coordinates clusters of neighboring cells Important in early development

Endocrine signaling Hormones released from a cell travel through circulatory system to affect other cells throughout the body Both animals and plants use this mechanism extensively

Synaptic signaling Animals Nerve cells release the signal (neurotransmitter) which binds to receptors on nearby cells Association of neuron and target cell is a chemical synapse

Signal transduction Events within the cell that occur in response to a signal When a ligand binds to a receptor protein, the cell has a response

Receptor Types Receptors can be defined by their location Intracellular receptor – located within the cell Cell surface receptor or membrane receptor – located on the plasma membrane to bind a ligand outside the cell Transmembrane protein in contact with both the cytoplasm and the extracellular environment

Intracellular Receptors Steroid hormones Common nonpolar, lipid-soluble structure Can cross the plasma membrane to a steroid receptor Binding of the hormone to the receptor causes the complex to shift from the cytoplasm to the nucleus Act as regulators of gene expression (turning it on or off)

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Insulin receptor Activated receptor has sites that allow docking Insulin is a hormone that helps to maintain a constant blood glucose level Lowers blood glucose

**Cell-to-Cell Interactions Cells can identify each other by cell surface markers Different receptors can produce the same messengers Hormones glucagon and epinephrine can both stimulate liver cells to mobilize glucose Different signals, same effect Both act by same signal transduction pathway

Existence of multiple forms (isoforms) of the same receptor Single signaling molecule can have different effects in different cells Existence of multiple forms (isoforms) of the same receptor Receptor for epinephrine has 9 isoforms Encoded by different genes Sequences are similar but differ in their cytoplasmic domains Different isoforms activate different proteins leading to different signal transduction pathways