BIOL 118 1st Edition Lecture 10Outline of Last Lecture I. Review of Plasma Membrane Structure & FunctionII. Primary Cell WallIII. Extracellular MatrixIV. How Do Adjacent Cells Connect and Communicate?V. Connections Between Animal CellsVI. Molecular Basis of Selective AdhesionVII. Cell Communication via Cell-Cell GapsVIII. Summary of Eukaryotic Cell-Cell AttachmentsIX. How Do Distant Cells CommunicateX. Steps of Cell-Cell SignalingOutline of Current Lecture I. Steps of Cell-Cell SignalingCurrent LectureSteps of Cell-Cell Signaling- #1: Signal Receptiono Signal receptors are bound by Hormones Other cell-cell signalso The presence of an appropriate receptor protein dictates which cells will be able to respond to a particular hormoneo Identical receptors in diverse cells and tissuesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Allow long-distance signals to coordinate the activities of cells throughouta multicellular organismo Signal receptors Are proteins that change their shape or activity after binding to a signaling molecule Are dynamic May change in their sensitivity to particular hormones Can be blockedo Signal receptors that bind to lipid-soluble hormones are located inside the cello Other signal receptors are located in the plasma membrane those that cannot cross the plasma membraneo A secondary name for what binds to the receptor: ligand- #2: Signal Processingo Lipid-soluble hormones that cross the plasma membrane produce different cell responses that lipid insoluble hormones that bind to membrane receptorso Lipid-soluble steroid hormones Bind to receptors inside the cell Trigger a change in the cell’s activity directlyo The hormone-receptor complex Is transported to the nucleus where it alters gene expressiono Hormones that cannot diffuse across the plasma membrane bind to membrane receptorso When a signal binds at the cell surfaceo The message transmitted by a hormone is amplified as it changes formo Signal transduction occurs at the plasma membrane changing of a signal to another form Involves G proteins or enzyme-linked receptors Enzyme-linked receptors trigger the activation of a series of proteins inside the cell Convert extracellular messenger to an intracellular signalo G Proteins Trigger the production of an intracellular messenger Intracellular peripheral membrane proteins Closely associated with transmembrane signal receptors When activated by receptor they trigger the production of messengers inside the cell Link the receipt of an extracellular signal to the production of an intracellular signal Activated when they bind GTP Deactivated when they hydrolyze the bound GTP to GDPo Linking an internal signal to the production of an intracellular signal involves 3 steps: Hormone binds to the membrane receptor- Changes shape - Activates G protein G protein exchanges GDP for GTP- Splits into 2 parts One part of the G protein activates a membrane enzyme- Catalyzes the production of a second messengero Second Messengers Small molecules Diffuse rapidly throughout the cell Amplify the hormone signal Several second messengers work by activating protein kinases- Kinases add a phosphate group to other proteins (phosphorylate)o Enzyme-Linked Receptors Transmembrane proteins Bind a hormone signal Directly catalyze a reaction inside the cell The receptor tyrosine kinases (RTKs) are the best known group of enzyme-linked receptorso Receptor Tyrosine Kinases & Signal Transduction Directly catalyzing an intracellular reaction involves 5 steps:- Hormone binds to an RTK- RTK forms a dimer and is phosphorylated by ATP- Proteins build a bridge between RTK, and the Ras protein is subsequently activated- Ras trigger the phosphorylation and activation of another protein- Phosphorylation cascade amplifies the original signal many times over o Each phosphorylated protein catalyzes the phosphorylation of other proteinso Results of Signal Processing Many of the key signal transduction events observed in cells occur via- G Protein- Enzyme-linked receptors The signal transduction event has 2 results:- Easily transmitted extracellular message is converted into an intracellular message- Original message is often amplified many times over- #3: Signal Responseo The ultimate response to a cell-cell signal varies from signal to signal and from cell to cello Falls into 2 categories A change in which genes are being expressed in the target cell Activate or deactivate a particular target protein that already exists in the cell- #4 Signal Deactivationo Turning off cell signals is just as important as turning them ono Cells have automatic and rapid mechanisms for signal deactivationo The mechanisms allow the cell to remain sensitive to small changes in The concentration of hormones The number and activity of signal receptorsSignal transduction pathways form a network allow the cells to respond to signals in a variety of
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