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3.D.1 Cell Communication Reflects Shared Ancestry
Cell communication processes share common features that reflect a shared evolutionary history.
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Communication involves transduction of signals from other cells, organisms, or the environment.
Steps of Signal Transduction: Reception Transduction Response
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In signal transduction, a ligand binds to a protein receptor on the cell membrane. That signal is then transformed into a signal inside the cell, which produces a specific cellular response.
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Signals can be stimulatory or inhibitory.
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Signal transduction processes are generally under strong selective pressure.
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In single-celled organisms, signal transduction pathways influence how the cell responds to its environment.
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Example: In quorum sensing, microbes use chemical messengers to communicate with other nearby cells and to regulate specific pathways in response to population density.
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Example: Response to external signals by bacteria that influences cell movement.
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In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole.
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Example: Epinephrine stimulation of glycogen breakdown in mammals
Example: Epinephrine stimulation of glycogen breakdown in mammals. (Model of a G-protein Receptor)
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Glycogen is a polysaccharide made from branching chains of glucose.
Glucose is stored as glycogen predominantly in liver and muscle cells. Glycogen functions as a long-term form of energy storage of carbohydrates.
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Muscular activity or its anticipation leads to the release of epinephrine (adrenaline) from the adrenal medulla. Epinephrine stimulates glycogen breakdown in muscle and, to a lesser extent, in the liver (the liver is more responsive to glucagon).
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The signal molecule epinephrine (ligand) binds to a specific receptor in the plasma membrane.
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When the ligand binds, the receptor changes conformation
When the ligand binds, the receptor changes conformation. This activates a G protein bound to the receptor. The activated G protein detaches when GDP is replaced by GTP.
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The G protein activates the transmembrane protein adenylate cyclase
The G protein activates the transmembrane protein adenylate cyclase. Adenylate cyclase catalyzes the formation of the secondary messenger cAMP from ATP.
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Cyclic AMP (cAMP) activates a protein kinase, which stimulates a phosphorylation cascade that amplifies the hormone signal.
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A protein kinase adds a phosphate group: phosphorylation.
A protein phosphatase removes a phosphate group: dephosphorylation.
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Cellular response: glycogen is broken down into glucose.
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Learning Objectives: LO 3.31 The student is able to describe basic chemical processes for cell communication shared across evolutionary lines of descent. [See SP 7.2] LO 3.32 The student is able to generate scientific questions involving cell communication as it relates to the process of evolution. [See SP 3.1] LO 3.33 The student is able to use representation(s) and appropriate models to describe features of a cell signaling pathway. [See SP 1.4]
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