Cell Communication

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Cell Communication

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University of Southern California
Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 4 Current Lecture Cellular Communication There are two basic types of physiological signaling: electrical signals (changes in a cell’s membrane potential), and chemical signals (molecules secreted by cells into the extracellular fluid). 4 basic methods of cellular communication: 1. Gap junctions: direct cytoplasmic passage of metabolites, 2nd messenger molecules, or ions between adjacent cells 2. Contact-dependent signaling: surface molecules on one cell membrane bind to surface molecules on another cell’s membrane 3. Long distance communication: combination of electrical signals carried by nerve cells and chemical signals transported in the blood a. Endocrine signaling: cell secretes substances, which can travel through blood circulation to a distant location to bind a target cell with a specific receptor. (ex. hormones) b. Pheromone: chemical signal that triggers a natural response in another individual of the same species 4. Local communication: chemicals diffuse through ECF, limited in distance a. Paracrine signaling: cell secretes substances, which diffuse through the ECF and affect nearby cells. (ex. metabolite or neurotransmitters) b. Autocrine signaling: signal acts on the same cell that secreted it in the first place Synaptic transmission is a special case that is a combination of long distance and local(paracrine in this case) signaling – electrical signals travel along a neuron until it reaches the end where it is translated into a chemical signal called a neurotransmitter that is secreted and diffuses across a narrow extracellular space to target a cell and incite a rapid cellular response. Mechanisms of Hormone Action A hormone is a chemical released by a cell or gland in one part of the body that sends out messages that affect cells in other parts of the organism. They are classified as hydrophilic(water soluble) or lipophilic(lipid soluble). 3 pathways: 1. Hydrophilic hormone, which can’t cross the membrane, has to bind to plasma membrane receptors, which is activated and in turn activates an intracellular second messenger system which alters enzyme activity, causing a response (directly or via a change in gene expression) 2. Lipophilic hormone, which is not freely soluble in the plasma, needs carrier proteins in the plasma and the ECF to transport it around. The unbound portion can diffuse directly through the plasma membrane and bind to a cytoplasmic or nuclear receptor. The hormone receptor complex then moves into the nucleus and binds directly to DNA, becoming a transcription factor that activates other transcription factors and directly affects gene expression. For most lipophilic hormones. There are specific carrier proteins (usually globular) that bind it with much higher affinity than any other hormone. There also exist carrier proteins that can bind indiscriminately to many lipid hormones. (ex. the most abundant protein in the plasma, albumin) 3. Lipophilic hormone that binds to plasma membrane receptors and activate 2nd messenger systems. Discovered while studying progesterone, a lipophilic hormone - they found plasma membrane receptors for it. There are similar receptors for testosterone and estrogen. Herrera Side note: Brown fat – highly metabolically active, its in babies because they use it to ...

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