cell communication

cell communication - cells can signal to eachother and interpret signals they receive from other cells and the environment - cell to cell communication allows cells to coordinate responses - signals are chemicals local signaling - free passage of substances in cytosol from one cell to another - signal moleucles are secreted by signaling cell - local regulators travel only short distances - growth factors stimulate nearby cells to grow and divide pancreatic signaling: local signaling in animal cells synaptic signaling: electrical signal moving along nervy cell that triggers secretion of neurotransmitters long distane signaling - plants and animals use hormones animals: called endocrine signaling; specialized cells release hormonesthat travel via circulatory system ex: insulin from pancreas allows cells to sequester blood and glucose 3 stages of cell signaling reception: detection of signal from outside/inside the cell transduction: signal caarried along pathway of relay molecules response: singla triggers response reception - binding between ligand (signal molecule) and specific receptor = induces shape change in receptor - most signal receptors are plasma membrane proteins but some are intracellular GPCR: G protein coupled receptors - cell surface transmembrane receptors that work with a g protein - g proteins are activated by GTP steps of GPCR 1) signal binds to receptor = changes shape and activates it 2) active receptor binds and activaetes a protein as gdp is swapped with gtp 3) activator g protein leaves receptor and diffuses along the membrane and binds and activates to the enzyme, stimulating a cell response 4) g protein hydrolyzes GTP back to gtp, making it inactive again RTK: receptor tyrosine kinases - membrane receptors that transfer phosphate groups from atp to themselves and activate relay protenis - can trigger multiple signal transduction pathways at once - abnormal functioning of RTKs are found in cancer/breast cancer steps of RTK 1) signal molecules bind to 2 RTK 2) TRK forms dimer (pair up) activating kinase area 3) RTK transfers phosphates from ATP to tyrosines (autophosphorylation) and activates relay proteins 4) a RTK (via relay protein) can trigger multiple signal transduction pathways at once ligand gated ion channel - acts as a "gate" that opens and closes when receptor changes - when signal molecule binds as ligand to receptor, gate allows/prevents specific molecules (like Na+) from entering steps of ligand gated ion channel 1) ligand binds to channel 2) channel opens/closes upon binding and ions flow (facilitation diffusion) through, triggering response 3) ligand falls off and the channel closes again intracellular receptors - in cytoplasm or nuculeus of target cells - small or hydrophobic messengers can cross membrane and activate receptors ex: steroids - activated hormone-receptor can act as a transcription factor, turning on specific genes transduction - disperse message in cell and can greatly amplify signal - receptor activates another protein, which activates another, until protein producing response is activates (relay molecules) - at each step, signal is transduced into differernt forms = shape change in protein protein phosphorylation and dephosphorylation - widespread mechanism for regulating protein activity - many relay moelcules are protein kinases, which leads to phosphorylation cascade phosphorylation: protein kinases transfer phosphate from ATP to a protein, activating protein dephosphorylation: protein kinases remove phosphate from protine, releasing the phosphate ion and inactivating itn steps 1) relay molecule activates protein kinase 1 2) active kkinase 1 activates protein kinase 2 3) active protein kinase 2 phosphorylates protein causing cell response to signal 4) protein phosphates (pp) catalyzes removal of phosphate groups from proteins, making them inactive again second messengers: cAMP (cyclic AMP) - small nonprotein, water soluable molecules/ions that disperse signaling inside cells and amplify it adenylyl cyclase: enzyme in plasma membrane, converts atp to cAMP - can activate many cAMPs amplifying response as long as epinephrine is present cAMP turns into AMP via phosphodiesterase signal amplification: exponential increase in the number of activated molecules at each step of signaling patwhway, so a single signal molecule can produce massive response epinephrine mobilizes glycogen in fight or flight response - change in gene expression (transcription factor) - change in cell metabolism; regulating synthesis of enzymes - change in membrane potential: opening/closing of ion channels (cell membrane) specificity of cell signaling - different cell types have different collectiosn of proteins, including different cell recprots, which can affect how they respond to signals (cell a) - pathway brancing (cell b) and "cross talk" (cell c) help cell cordinate incoming signals - same signal can have different affects in different cell types (cell d) ex: epinephrine - in liver cells, epinephrine binds to receptor (b) > glycogen breaks down and glucose is released > blood glucose level increases - in smooth muscle cell that supplies skeletal muscles, epinephrine binds to receptor (b) > cell relaxes > blood vessel dilates, increases flow to skeletal muscle - in smooth muscle cell that supplies intestines, epinephrine binds to receptor (a) > cell contracts > blood vessel constricts and decreases flow to intestines termination of signal - if signaling molecule concentration fails, fewer molecules will be bound on receptors, unbound receptors revert to inactive state - cAMP > AMP = phosphodiesterase inactivates cAMP signal by converting it into regular inactive noncyclic adenosine monophosphate (AMP) tastebuds have many. chemical receptros, binding of one sugar molecule triggers signal transduction sugar > receptor > G proteins > adenylyl cyclase > cAMP > kinase A > K+ channels close > depolarized > Ca 2+ enters > neurotransmitters release