Cell Communication Chapter 9 Overview Communication between cells

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 2

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• There are four basic mechanisms for cellular communication 1. Direct contact 2. Paracrine signaling 3. Endocrine signaling 4. Synaptic signaling • Some cells send signals to themselves (autocrine signaling) 4

Direct contact • Molecules on the surface of one cell are recognized by receptors on the adjacent cell • Important in early development • Gap junctions 5

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 6

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 7

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 8

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 9

Receptor Types • Receptors can be defined by their location 1. Intracellular receptor – located within the cell 2. 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 10

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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) 12

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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 15

**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 16

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• 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 18