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UI BIOL 1411 - Cell Signaling Continued

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BIOL 1411 1st Edition Lecture 9Outline of Last Lecture 1. Active transport2. Macromolecules leaving the cell3. Cell responding to their environment4. Receptors sense signals Outline of Current Lecture 1. Extracellular signal transduction2. Cell’s response from signal3. Direct cell-cell interaction and communicationCurrent LectureChunk 3: How is an extracellular signal continued or “transduced” to actually affect the cell?(Chunks 1-2 are from last lecture)Transduction and Amplification of the Signal- In most cases, Receptor-Ligand complex does not itself produce the effects in the target cells- Signal transduction events mediate the effects of signal-receptor binding o Direct signal transduction Occurs at plasma membrane and results from the receptor itself initiating cellular response by effector proteinso Indirect signal transduction Other molecules mediate and amplify the original signal inside the cellThese 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.- Receptorprotein kinasescell response - G protein-linked receptorscAMPcell responses- Protein kinase cascadeso Are often used as signal transducers and amplifiers (both direct and indirect)o Several kinases, in which each one phosphorylates and activates the next In direct transduction, the first kinase is the activated receptor o At each step, signal is amplified because each kinase can phosphorylate many target moleculeso Information that arrived at the plasma membrane can be communicated to the nucleuso Many steps provide specificity—different target proteins provide variation in respose- Second messengero A cytoplasmic molecules produced as a result of membrane receptor-ligand interaction mediates the cell’s response to the signal (the first messenger)o Cyclic AMP Discovered in liver cells as the intermediate between the epinephrine receptors in the membrane and the cytoplasmic enzyme glycogen phosphorylase Made from ATP by adenylyl cyclase enzyme Two major target types:- Binds to ion channels in many kinds of sensory cells and opens the channel- Binds to protein kinases in cytoplasm and start a protein kinase cascade o Discovery of a second messenger Soluble chemical, produced by the hormone-activated membranes, activated glycogen phosphorylaseo Indirect Signal Transduction through Second Messengers Common means of signal transduction- 2nd messenger effect many processes and allow a cell to respond in many ways to a single event at the plasma membrane- 2nd messengers greatly amplify the signal- 2nd messengers are not themselves proteins but act as cofactors or regulators of a variety of target proteins (channels or enymes) Common 2nd messengers- cAMP- Inositol triphosphate (IP3) and diacylglycerol (DAG)o Derived from phospholipid PIP2 (phosphatidyl inositol biphosphate) in the plasma membrane DAG- Hydrophobic part, embedded in plasma membrane IP3- Hydrophilic part, projects into cytoplasmo Are second messengers for signals that bind to G protein linked receptor o How it works Signal binds G protein-linked receptor; G protein swaps GDP and GTP and becomes active Activated G protein subunit encounters and activates phospholipase C, which cleaves off IP3 from PIP2 DAG stats in the membrane IP3 diffuses thru cytoplasm and contacts Ca++ channels in ER, causing Ca++ ions to enter cytoplasm Ca++ ions and DAG together activate membrane-bound protein kinase C (PKC)- Both IP3 and DAG are needed to activate PKC PKC mediates cellular responses to the signal (first messenger)- Calcium ions (Ca++)- Nitric oxide (NO)- Signal transductiono Cells regulate activity of transducer molecules to respond to signal and then return to original state to MAINTAIN RESPONSIVENESS  NO is unstable, its concentration is regulated by how much is made Cytoplasmic concentration of Ca2+ depends on activity of membrane pumps andion channels Protein kinases, G proteins and cAMP are regulated by enzymes that convert theactivated form back to inactive formo The balance between enzymes that activate transducers and enzymes that inactivate them determines the cellular response to a signalChunk 4: What are some activities a cell does in response to a signal?- Effects depend on the type of cell and the signal- Nervous system cellso Acetycholineopening of ion channels- Cells involved in nutrient metabolism and maintain internal homeostasis (like liver cells)o Epinephrinechange in enzyme activities to increase blood glucose levels- Actively dividing or differentiating populations of cellso Growth factors, steroid hormonesdifferential gene transcription to make new proteinsChunk 5: Direct Cell-Cell interaction and Communication- Cells of multicellular organisms also have direct mechanisms of interaction- Tissue formation and maintenance o Cell-cell recognition: Involves carbohydrates and proteins on plasma membrane of cell wall- Direct cell-cell communication mechanismso Gap junctions in animalso Plasmodesmata in plants- Communicating Junctions (part 1)o Gap junctions are formed from two Connexons, each made from connexin proteinso The passageway is too small for macromolecules o ATP, small sugars, amino acids, and 2nd messengers can pass- Plant Cellso Have several thousand plasmodesmata (membrane-lined tunnels) that traverse the cell wallso Lining made of fused plasma membranes from both cells; creates a continuous cytoplasmo A desmotubule, derived from the ER, fills the space in the plasmodesmata channelo Allows rapid transmission of small molecules, including plant


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