Cell Communication Tutorial Notes

responses to signals ion channels open or close, enzyme activity change, gene is activated on/off Describe the sequence of events that takes place in cell signaling. - A cell sends a signal by releasing signaling molecules. - The signal is transported to the target cells, if the target cells are not close to the signaling cell. - The target cell receives the signal by the process of reception. three types of signaling molecules local regulators, neurotransmitters, hormones - Local regulators are cell signaling molecules that communicate with nearby cells. - Neurotransmitters are cell signaling Describe three types of signaling mole- molecules cules: released by neurons that relay nerve imlocal regulators, neurotransmitters, and pulses to hormones. other neurons or muscle cells. - Hormones are cell signaling molecules typically transported by blood in the circulatory system Identify mechanisms that make reception a highly specific process. specific shape / a receptor binds to a specific molecule because they are genetically programmed to match. - Receptor-up regulation occurs in response to low hormone concentration. The cell proWhat are receptor up-regulation and duces more receptor down-regulation and when/how receptors on the cell membrane in an effort to bind to the few hormone molecules available. - Receptor-down regulation might occur 1/6 do they occur? if the signaling molecule, such as a hormone like insulin, remains at high concentration for an extended period of time. What are the three types of cell-surface receptors? Ion channel-linked receptors. G protein-linked receptors. Enzyme linked receptors action of ion channel-linked receptors action of G Protein-Linked Receptors the binding of the signal molecule causes the opening or closing of the ion channel. - For example, the binding of GABA neurotransmitter in the neuron causes the chloride channel to open. Chloride ions flood into the neuron, inhibiting the transmission of the nerve impulse by hyper-polarizing the membrane. - Neurotransmitter binds to G protein-linked receptor G protein is activated - Activated G protein controls production of second messengers, e.g., cyclic AMP, cyclic GMP, diacylglycerol or Ca2+ - causes the receptor tail to change shape in the cytoplasm side of the membrane. The tail releases GDP to be replaced by GTP which then activates a nearby enzyme. 2/6 action of enzyme-linked receptors binding of the signal molecule results phosphorylation of the cytoplasmic portion of the enzyme which can activate/phosphorylate other enzymes When a hormone binds to a receptor protein on the cell membrane of a target cell (adenyl cyclase) , the protein stimulates the production of a second messenger called cyclic AMP (from ATP). The cAMP molecule then triggers various enzymes, leading to a specific cellular change. cyclic AMP (cAMP) (second messenger - Ex. cAMP activates protein kinase A, which in transduction) phosphorylates a target protein. P + ADP = ATP Phosphorylation 3/6 DAG and IP3 DAG - produces protein kinase C which phosphorylates(adds phosphate) to proteins to create response in cell IP3 - binds to calcium channels in ER and opens them to increase amount of calcium in cytosol, which creates response position enzymes of signaling complexes to align with their substrates so those enzymes are not utilized in other pathways. have multiple binding sites; have 1 signal to release several. what do scaffolding proteins do/how do they work? - Ion channels opening or closing Describe three types of responses that - Enzyme activity being altered (leading cells to make to signals. changes in metabolic activity) - Specific genes being turned on or off. 4/6 turns one signal molecule into multiple second messenger molecules. signal amplification signal termination - Examples include cAMP actviating an enzyme protein kinase, which phosphorylates many protein molecules. This amplification continues when activated enzymes activate other enzymes or catalyze other proteins. Further amplification occurs when these enzymes act on multiple substrate molecules. process that stops signal transduction. returns the receptor and each of the components of the signal transduction pathway to their inactive states. - Quorum sensing in prokaryotes - Signaling between plants and insects (p. 135) - Similar, but not identical, receptors and Cite evidence supporting a long evolu- intracellular signal molecules are found tionary in history for cell signaling molecules. organisms of all kingdoms. - Important proteins necessary for cell communication in animals have been found in choanoflagellates. 5/6 types of signals growth factor, histamines, prostaglandins, nitric oxide, neurotransmitters (all local), endocrine glands (distant) types of receptors large proteins, glycoproteins, ligands binding, intracellular, rhodopsin, phytochrome types of signal transduction ion channels, g protein linked, enzyme linked, second messengers, transcription factors (intracellular), nitrous oxide, scaffolding proteins 6/6