General Biology Week 8
General Biology Week 8 1305
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This 6 page Class Notes was uploaded by Ruby Vargas on Friday October 14, 2016. The Class Notes belongs to 1305 at University of Texas at El Paso taught by Roychowdhury in Fall 2016. Since its upload, it has received 6 views. For similar materials see General Biology in Science at University of Texas at El Paso.
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Date Created: 10/14/16
The membrane Plays a Key Role in a Cell's Response to Environment Signals Cell Signaling = Cells can process information form their environment o Signals include physical stimuli, light and heat, sound, chemicals (ligands) such as hormones. o Cell must have a receptor for the signal in order to respond. o Following signaling receptor, signal transduction pathway is initiated a sequence of events that lead to a cellular response. A signal transduction pathway involves a signal, a receptor, and a response . Multicellular animal cells are exposed to chemical signals": o Autocrine signals affects same cells that release them. o Paracrine Signals diffuse to and affect nearby cells. o Hormones travel to distant cells usually via circulatory system. Allosteric regulation Common mechanism of signal transduction. o Alteration in a protein's shape as a result of a molecule binding to it. o Signal receptor= short/long term responses. Membrane proteins act as receptors. o Signal molecule/ ligand fits into 3D site on receptor protein. o It then alters the 3D shape o Initiates cell response. Ligands, not metabolized further. Binding may expose active site on the receptor. Binding = reversible o ligand can be released to end stimulation. Inhibitor/ Antagonist can bind in normal ligand, preventing receptor activation by the ligand. Intracellular receptors= located inside a cell. o Ligands are small or nonpolar (non covalent) and may diffuse across the membrane. o Ex. Estrogen, a lipid, soluble steroid hormone diffuse easily into the sells and binds to estrogen receptors, an intracellular receptor. Membrane Receptors located on the surface of the cell. o They obtain a larger polar ligands that cannot diffuse through the membrane. o Receptor may have catalytic domain on the cytoplasmic side. Ligand is an allotropic egulator which exposes the active site on the catalytic domain. Reverable binding needed to stop responding to a signal after adequate response has occurred. Inhibitor/ Antagonists can bind in place of normal ligand. o Caffeine binds to receptors in the brain, preventing binding by normal ligands. Membrane Receptors classified by their activity: 1. Ion Channel receptors o Gated channels, and they alter their 3D shape when ligand binds. o Acetylcholine receptor A gated sodium binds to the acetylcholine to open the channel and allow Na+ to diffuse into the cell. 2. Protein Kinase receptors o Alters shaped when it binds. o New shape activates a cytoplasmic domain that has catalytic (protein kinase) activity. o Not all protein kinases are receptors. ATP+Protein = ADP +phosphorylated o Each protein kinase has a specific target protein, and it's activity is changed when it is phosphorylated. 3.GProtein linked receptors o ligand binding occurs on surface that exposes a site on the cytoplasmic side of the receptor that binds to a mobile membrane protein. o GTP, GDP binding proteins o G protein partially inserted in the lipid bilayer and partially exposed on cytoplasmic surface. o alpha, beta, and Gama o alpha is subunit for GTP/GDP binding o both subunits activate different effector proteins (amplification to termination of the signal) o GTP terminates signal by allowing G alpha to bind to G beta and gamma and inactivate G alpha beta gamma Cell Functions change in response to environment Activation leads to response by a signal transduction pathway Initial signal is amplified and distributed to cause different responses. = changes cell's function Ways cells respond to environme sign s: o Opening of ion channels changes the balance of out and inside the cell. =change in electrical potential across membrane o Alterations in a gene expression genes may switch up/off. This affects the abundance of proteins (often enzymes),= changing cell function o Alteration of enzyme activities rapid response. Same signal may result in different responses in different cells. Ex. Heart and digestive trat muscle cells respond differently to epinephrine because the signal transduction pathways stimulated are different in the 2 cell types. Second Messengers can stimulate signal transduction o intermediate between the receptor and the cascade of responses. o Discovered by Sutherland and his colleges on liver enzyme glycogen phosphorylase and how it is activated by hormone epinephrine. o Binding the 1st mssenger to the membrane receptor caused production of small molecule, cAMP (2nd messenger) that diffuse into the cytoplasm to activate the enzyme. o Enzyme= catalyzes breakdown of glycogen stored in the liver so that glucose can be released in the blood to provide quick energy. Signal=1st messenger 2nd messenger =released into cytoplasm after signal binds to receptor. o Allows the cell to respond to single membrane event with many events inside the cell. o Distribute the signal They amplify the signal by activating more than one enzyme target. o 1 epinephrine= production of many cAMP cAMP= common 2nd receptor o Activates enzyme targets o produces and activates protein kinase A which phosphorylates two other enzymes with opposite effects in glucose metabolism Adenylyl is the formation of cAMP o Located on the cytoplasmic side of the plasma membrane o Activated by G proteins Epinephrine binds to receptor and activates a G protein Signal Transduction is highly regulated. o Signal transduction= temporary events in the cell. (turns on and off) o It ends when cell responds. Enzymes covert each transducer back to its inactive precursor. o Balance between regulating enzymes and the signal enzymes determines the cell's response. 2 ways cells can alter the balance of enzymes: 1. Synthesis or breakdown of the enzyme 2. Activation or inhibition of the enzymes by other molecules. What role does the cell membrane play in the body''s response to caffeine? o Caffeine= large molecules (polar) binds to nerve cell receptors in the brain. o Structure similar to adenosine, which binds to receptors after activity or stress and results in drowsiness. o Caffeine binds with same receptor but does not activate it. Result=Person remains aler
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