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Biological Science
BISC 160
Dr.Beckie Symula

Chapter 7 9/8/2013 7:50:00 AM 7.1 What are signals, and how do cells respond to them?  Cells receive signals from the physical environment and from other cells o Humans: light, odor, taste, temperature, touch, sound o Bacteria: minute chemical changes o Plants: light and temperature o Cells receive signals from extracellular fluid environment and can respond to changes in the extracellular concentrations of certain chemicals such as CO 2nd H + o Chemical signals reach a target cell by local diffusion or circulation within blood o Autocrine: signals diffuse to and affect the cells that make them  Tumors reproduce uncontrollably because of self- stimulation o Paracrine: signals diffuse to and affect nearby cells  Neurotransmitter made by one nerve cell that diffuses to an adjacent cell and stimulates it  A signal transduction pathway involves a signal, a receptor, and responses o In a multicellular organism, all cells may receive chemical signals that are circulated in the blood  Signal o A cell must perceive and quickly respond to environmental signal  Receptor o E. coli receptor for protein is EnvZ. (transmembrane) o When solute concentration, EnvZ changes its shape in response o The cytoplasmic domain of EnvZ can act as an enzyme, changing of shape exposes an active site so that EnvZ becomes a protein kinase—enzyme that catalyzes transfer of a phosphate group from ATP to another molecule o EnvZ phosphorylates itself o Phosphorylation leads to a change in the shape and function of a protein by changing its charge  Responder o The charged phosphate group that was attached to the EnvZ causes its cytoplasmic domain to change shape again. It now binds to a second protein, OmpR, and transfers the protein to it. This changes shape of OmpR o OmpR binds to ompC DNA, resulting in an increase in transcription of that gene o OmpC is produced and it is inserted in the outer membrane where it blocks solutes from entering the intermembrane space o 1. A receptor protein changes its conformation upon interaction with a signal. This receptor protein may or may not be in a membrane. 2. A conformational change in the receptor protein activates its protein kinase activity, resulting in the transfer of a phosphate group from ATP to a target protein 3. This phosphorylation alters the fun
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