signal transduction pathway
process where signal on cell surface is converted to specific cellular response
signal transduction pathway (yeast)
(1) exchange mating factors- binds to receptors on other cell type. (2) mating- beginning of cell fusion. (3) new fused cell- includes all genes from both cells
type of local signaling. cell can receive and respond to factors produced by single cell in vicinity. example: growth factors
stages of cell signaling
reception. transduction. response
target cell detects signaling molecule from outside cell. molecule binds to receptor protein
converts the signal to a form that can bring about a specific cellular response
transduced signal triggers specific cellular response
molecule that specifically binds to another molecule
binding causes receptor protein to change shape. mostly it activates the receptor to interact with other molecules. can also cause 2 or more receptors to combine
plasma membrane proteins. ligands are water soluble
G-protein coupled receptors
plasma membrane receptor that works with a G protein (protein that binds energy molecule GTP).made of 7 alpha helixes. extremely widespread and diverse. G-protein systems involved in many human diseases
receptor tyrosine kinases
kinase- enzyme that catalyzes transfer of phosphate groups. receptor functions as tyrosine kinase- enzyme that catalyzes transfer of phosphate group from ATP to the amino acid tyrisine on substrate protein. **membrane receptors that attach phosphates to tyrosines
ligand-gated ion channel
region acts as a gate when the receptor changes shape. can open or close when a ligand binds to receptor
transduction stage: multistep pathways
benefits: (1) can greatly amplify a signal (2) provide more opportunities for coordination and regulation--allows fine-tuning of response
are signal molecules passed along a signaling pathway?
no. usually doesnt even enter cell. information is passed on. ie domino effect.
series of different molecules in a pathway are phosphorylated; each molecule adds a phosphate group to the next one. converts ATP to ADP
enzyme that transfers phosphate group from ATP to protein. cells may have hundreds of protein kinases, each specific for a different substrate protein
enzymes that rapidly remove phosphate groups from proteins (dephosphorylation). turn off the signal transduction pathway when initial signal is gone. also make protein kinases available for reuse. acts as a switch depending on balance btwn active kinase and active phosphatase
signal transduction components that are not proteins. they're small, water soluble molecules/ions. readily spread throughout cell by diffusion, and participate in G protein and tyrosine kinase receptors.
cyclic AMP (cAMP)
converted from ATP by adenylyl cyclase-enzyme in plasma membrane. acts as a second messenger and activates other proteins. broadcasts signal to cytoplasm
disrupting G-signal pathways
if G protein is modified (like by cholera bacterium), the G protein is unable to hydrolyze GTP to GDP. Therefore, continues to make cAMP.
Calcium and signal transduction
calcium used as second messenger. [Ca] in cytosol normal lower than [Ca] outside of cell. cell's Ca can rise bc of transport of Ca in by Endoplasmic Reticulum. In response, signal transduction, releases Ca from cell's ER from a cleavage produced in plasma membrane