BIOL 213 1st Edition Lecture 23 Outline of Last Lecture I. Signal transductiona. 5 different kinds of signalingII. Response to signalingIII. Intracellular receptorsa. Ex: nitric oxide and steroid hormonesIV. Cell surface receptorsa. 3 main kindsi. Ion channels, G-protein-coupled receptors, enzyme-linked receptorsb. Molecular switchesOutline of Current Lecture I. Cyclic AMPa. Produced by adenylyl cyclaseb. Primary target is PKAII. Inositol triphosphate (IP3), diacylglycerol (DAG), and Ca2+ a. IP3 and DAG are generated by phospholipase Cb. IP3 opens Ca2+ channels in the ER and Ca2+ and DAG activate PKCc. Ca2+ can bind to other proteins like calmodulin, which can then bind to CaM-kinaseIII. Enzyme-linked receptorsa. Receptor tyrosine kinases activate signaling proteinsb. PIP3c. RasThese 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.IV. Some pathways are activated only if multiple signals are presentV. ReviewVI. Plant signalingVII. Receptor downregulationCurrent LectureI. Cyclic AMPa. Many G-protein coupled receptors active adenylyl cyclaseb. This enzyme produces cyclic AMP from ATPi. It connects one oxygen from phosphate to an OH on the sugarii. 2 phosphates are removed from ATPc. There is a very low concentration of cyclic AMP inside an unstimulated cell compared to a stimulated celld. It is a second messengeri. It diffuses through the cell and interacts with other proteins to initiate a responsee. Cyclic AMP phosphodiesterase terminates the signali. It converts cyclic AMP to regular 5’ AMP ii. By breaking the bond between the oxygen and sugariii. Kinases add 2 phosphates to reform ATPiv. Caffeine blocks the phosphodiesterase so that the concentration of cyclic AMP stays highf. It’s primary target is cyclic-AMP-dependent protein kinase (PKA) i. PKA is activated when cyclic AMP binds to itii. This activated kinase then phosphorylates serines and threonines (amino acids) on specific proteinsg. Different target cells have different target proteinsi. This allows the effect of cyclic AMP to vary in different types of cellsii. Ex: adrenaline binds to adrenergic receptors1. Causes the breakdown of glycogen in skeletal muscle cellsh. Effects can be rapid or slow i. Rapid response is when a target protein is alteredii. Slow response is when transcription is regulated so that new proteins have to be synthesizedII. Inositol triphosphate (IP3), diacylglycerol (DAG), and Ca2+ a. Some G-protein coupled receptors activate the membrane-bound enzyme phospholipase C b. Phosopholipase C (with water) cleaves an inositol phospholipid called phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messangers: inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG)i. IP3 diffuses through the cytosol to bind to and open Ca2+ channels in the ER membrane1. Ca2+ diffuses into the cytosolii. DAG stays in the membraneiii. DAG and Ca2+ both bind to and activate protein kinase C (PKC) iv. PKC then phosphorylates other proteins in the cell to pass on the signalc. Ca2+ is a second messenger for many pathwaysi. Because the concentration of Ca2+ inside the cell is normally really low, whenever a high concentration is detected, the cell know that there was asignal1. A Ca2+ gradient is created across the ER membrane and the plasmamembraneii. Sometimes its effects can be indirect like when it binds to calmodulin 1. This is the most widespread2. When Ca2+ interacts with calmodulin, it changes its shape it so thatit can interact with several different target proteins3. An important kind of target protein is Ca2+ / calmodulin-dependentprotein kinases (CaM – kinase) a. These in turn phosphorylate other proteinsIII. Enzyme-linked receptorsa. These are transmembrane receptor protein where the cytoplasmic domain of theprotein either acts as an enzyme or forms a complex with other proteins that willthen act as an enzymeb. Most enzyme-coupled receptors have a cytoplasmic domain that functions as a tyrosine protein kinasei. These are called receptor tyrosine kinases (RTK)c. RTKs only have one transmembrane alpha helix, so it’s hard to translate a conformational change through thati. Therefore, two RTKs interact and activate each otherii. A signal molecule is in the form of a dimerd. The phosphorylated tyrosines on the tail of the RTK are docking sites for other proteinsi. Some of these proteins are phosphorylated and activatedii. Some are scaffolding for other proteinse. Tyrosine phosphatase inactivates the enzyme/complex by removing the phosphate groups from the tyrosines and bound proteinsf. Some RTKs activate an enzyme called phosphoinositide 3-kinase (PI3 kinase) thatwill phosphorylate PIP2 into PIP3i. This is the same PIP2 that is cleaved into IP3 and DAG by phospholipase Cii. PIP3 acts as a second messenger to activate other proteinsiii. PIP3 stays in the membraneiv. It activates protein kinase B (PKB, also known as Akt) which is important in the growth and survival of cellsg. Ras i. Ras is a small GTP-binding protein that nearly all RTKs activate1. They are a kind of monomeric GTPase that resembles the alpha region of a G-protein2. It is active when bound to GTP3. It is inactive when bound to GDPii. A signal molecule activates the RTKiii. An adaptor protein binds to the activated tyrosineiv. This activates the Ras-activating protein (Ras-GEF) v. Ras-GEF causes the inactive membrane-bound Ras to exchange GDP for GTPvi. Ras is now active and can pass on the signalvii. By initiating a phosphorylation cascade from the plasma membrane to the nucleusviii. This includes the MAP-kinase signaling module1. Ras activates MAP kinase kinase kinase2. Which activates MAP kinase kinase by phosphorylation3. Which activates MAP kinase by phosphorylation4. Which phosphorylates target proteins to initiate a responseix. Mutations involving the GTPase activity of Ras are found in about 30% of cancers1. The Ras protein is mutated so that it’s never inactivated and continues to transmit signals even without a signal molecule2. Because Ras is important in signaling cell growth, this mutation leads to uncontrollable cell growth3. Mutant genes that can lead to cancer are called oncogenesIV. Some pathways are activated only if multiple signals are presentV. Reviewa. G-protein linked receptors activate G-proteins by phosphorylation of GDP to GTPi. The α and β/γ subunits dissociate and activate other proteinsii. G-proteins