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UI BIOL 1411 - Sell Signaling and Communication

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BIOL 1411 1st Edition Lecture 9Outline of Last Lecture I. Transport of Large Molecules across membraneII. Cell Signaling a. Cells Respond to environmentb. Receptors sense signalsOutline of Current Lecture I. Cytoplasmic ReceptorsII. Transduction and Amplification of SignalIII. Direct cell to cell interaction and communicationCurrent LectureCytoplasmic receptors- Small nonpolar molecules and steroids can pass through the cytoplasmic membrane Big Idea 3: How is an extracellular signal continued or “transduced” to actually affect the cell?Transduction and Amplification of Signal- Receptor-ligand complex does not itself produce the effects in the target cell, most cases- Signal transduction events mediate the effects of signal-receptor bindingo Direct signal transduction: occurs at plasma membrane and results from receptoritself initiating cellular response by effector proteinso Indirect signal transduction: other molecules mediate and amplify the original signal inside the cell Receptor Protein Kinase  cell response G protein-linked receptors cAMP cell responseso Protein Kinase cascades: often used as signal transducers and amplifiers Several kinases, in which one phosphorylates and activated the next- In direct transduction, the first kinase is the activated receptor At each step, the signal is amplified Information that arrived at the plasma membrane can be communicated to the nucleus Many steps provide specificityo G protein-linked preceptor pathwayThese 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. Involves a second messenger- cytoplasmic molecules produced as a resultof membrane receptor-ligand interaction mediates the cell’s response to the signal First example: cAMP- Discovered in liver cells as the intermediate between the epinephrine receptors in the membrane and the cytoplasmic enzyme glycogen phosphorylase- cAMP is made from ATP by adenylyl cyclase enzyme- 2 major target types:o Binds to ion channels in many kinds of sensory cells and opens the channelo Binds to protein kinases in cytoplasm and starts a protein kinase cascade  Common means of signal transduction- 2nd messengers 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 acts as cofactors or regulators of a variety of target protiens Common second messengers- cAMP- IP3 and DAG- Ca++- NO PIP2 in plasma membrane creates 2 second messengers:- DAG hydrophobic part, embedded in plasma membrane- IP3: hydrophilic part, projects into cytoplasm- Both activate PKC that has a lost of targets in the cello How signal transductions are highly regulated Cells regulate the 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 and ion channels Proteins kinases, G proteins, and cAMP are regulated by enzymes that convert the activated form back to inactive formo What are some activities cells do once they receive a signal Effects depend on the type of cell and the signal Nervous system cells- Acetycholineopening of ion channels Cells involved in nutrient metabolism and maintaining internal homeostasis (liver cells)- Epinephrine Actively dividing or differentiating populations of cells- Growth factors, steroid hormoneso Odorant molecules bind to receptors in the nose, and a G protein is activated This activated adenylyl cyclase to catalyze formation of cAMP, which opens ion channelso A cascade of reactions leads to altered enzyme activity- Direct Cell to Cell interaction and communicationo Cells of multicellular organisms also have direct mecanisms of interactionso Tissue formation and maintenance Cell-cell recognition: involves carbohydrates and proteins on plasma membrane or cell wallo Direct cell-cell communication mechanisms Gap junctions in animals: made from 2 connexons, each made from connexin proteins, too small for macromolecules, ATP, small sugars, amino acids, 2nd messengers can pass Plasmodesmata in plants: membrane lined tunnels, desmotubule fills the space in the


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