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BIO OUTLINE UNIT I EXAM CHAPTER 11 11.1 Example of cell signaling is sex in yeast a and α cell types o a signal is released that binds to a receptor on the other type of cell o this causes the cells to grow towards each other, exchange genetic material and “mate” signal transduction pathway is the process by which a signal on a cell’s surface is converted to a specific cellular response in a series of steps Another example is quorum sensing in bacterial cells that allows them to coordinate their activities by sensing the local density of bacterial cells Local and Long-distance Signaling o Plants and animals have cell junctions so that adjacent cells can communicate (plasmodesmata in cell walls of plants) o Animal cells also have cell-cell recognition for adjacent cells o Local regulators (example = growth factor) travel short distanes and are used for local signaling, i.e. paracrine signaling o Synaptic signaling occurs in the animal nervous system an electrical signal uses chemicals to cross synapse o Hormones are used for long-distance signaling in plants and animals Three stages of Cell Signaling: o Reception : target cells detection of a signaling molecule coming fro outside the cell. Molecule binds to receptor o Transduction : binding of the signaling molecule changes the receptor protein in some way, initiating the process of transduction o Response The transduced signal finally triggers a specific cellular response 11.2 Signals bind to receptors that either change shape or aggregate to induce the cascade of the signal transduction pathway Receptors in the Plasma Membrane: Three Types G protein-coupled receptors, receptor tyrosine kinases and ion channel receptors o G protein-coupled receptors When GDP is attached to G protein it is inactive The G protein itself is loosely attached to he cytoplasmic side of the receptor When a signal binds to the receptor, the receptors shape changes and GTP displaces the GDP and activates the G protein The G protein leaves the receptor and triggers a signal pathway The G protein is eventually recycled by replacing the GTP with a GDP o Receptor Tyrosine Kinases
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Tyrosine kinases have a ligand binding site, an alpha helix spanning the membrane, and a polypeptide chain with tyrosines attached Binding of a signal molecule causes two receptor polypeptides to associate closely with each other (DIMERIZATION) Dimerization activates the tyrosine kinase region of each polypeptide and each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine on the tail of the other polypeptide The receptor protein is now recognized by specific relay proteins that bind to specific phophorylated tyrosines, undergoing structural changes that activate the bound protein triggers a transduction pathway o Ion Channel Receptors Signal molecules bind as ligand to channel receptor Causes conformational change that opens or closes the gate
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