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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

paracrine signal

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

ligand-receptor interaction

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

signal receptors

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.

phosphorylation cascade

series of different molecules in a pathway are phosphorylated; each molecule adds a phosphate group to the next one. converts ATP to ADP

protein kinase

enzyme that transfers phosphate group from ATP to protein. cells may have hundreds of protein kinases, each specific for a different substrate protein

protein phosphatase

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

second messenger

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

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