BIOL 118 1st Edition Lecture 10 Outline of Last Lecture I Review of Plasma Membrane Structure Function II Primary Cell Wall III Extracellular Matrix IV How Do Adjacent Cells Connect and Communicate V Connections Between Animal Cells VI Molecular Basis of Selective Adhesion VII Cell Communication via Cell Cell Gaps VIII Summary of Eukaryotic Cell Cell Attachments IX How Do Distant Cells Communicate X Steps of Cell Cell Signaling Outline of Current Lecture I Steps of Cell Cell Signaling Current Lecture Steps of Cell Cell Signaling 1 Signal Reception o Signal receptors are bound by Hormones Other cell cell signals o The presence of an appropriate receptor protein dictates which cells will be able to respond to a particular hormone o Identical receptors in diverse cells and tissues These 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 throughout a multicellular organism o 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 blocked o Signal receptors that bind to lipid soluble hormones are located inside the cell o Other signal receptors are located in the plasma membrane those that cannot cross the plasma membrane o A secondary name for what binds to the receptor ligand 2 Signal Processing o Lipid soluble hormones that cross the plasma membrane produce different cell responses that lipid insoluble hormones that bind to membrane receptors o Lipid soluble steroid hormones Bind to receptors inside the cell Trigger a change in the cell s activity directly o The hormone receptor complex Is transported to the nucleus where it alters gene expression o Hormones that cannot diffuse across the plasma membrane bind to membrane receptors o When a signal binds at the cell surface o The message transmitted by a hormone is amplified as it changes form o 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 signal o 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 GDP o 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 messenger o 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 receptors o 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 proteins o 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 Response o The ultimate response to a cell cell signal varies from signal to signal and from cell to cell o 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 Deactivation o Turning off cell signals is just as important as turning them on o Cells have automatic and rapid mechanisms for signal deactivation o The mechanisms allow the cell to remain sensitive to small changes in The concentration of hormones The number and activity of signal receptors Signal transduction pathways form a network allow the cells to respond to signals in a variety of ways
View Full Document
Unlocking...