Cell Communication

Chapter 11

• Cells need to communicate between themselves to maintain homeostasis.

• Process by which signal on cell’s surface converted into specific cellular response consists of series of steps - signal-transduction pathway.

http://www.mpi-dortmund.mpg.de/departments/dep1/signaltransduktion/image3.gif

• Yeasts communicate between 2 types of yeast cells to reproduce.

• 2 sexes, a and alpha - secrete specific signaling molecule, a factor and alpha factor.

• Factors find each other and bind to each other’s receptors.

• Also occurs in multicellular organisms.

• Some cells release local regulators - influence cells in local vicinity.

• Synaptic signaling - nerve cell produces neurotransmitter that diffuses to single cell - is almost touching sender.

• Nerve signals travel along series of nerve cells without unwanted responses from other cells.

• Plants, animals - hormones to signal at greater distances.

• Cells may communicate by direct contact.

• Signaling substances dissolved in cytosol pass freely between adjacent cells.

• 3 stages to signal transduction. • 1Reception - chemical signal

binds to cellular protein at cell’s surface.

• 2Transduction - binding leads to change in receptor that triggers series of changes along signal-transduction pathway.

• 3Response - transduced signal triggers specific cellular activity.

• Receptor proteins present on cells to recognize signal molecules.

• Ligand - molecule that binds to another molecule, causes cell to change shape when attached to cell’s receptor.

• Receptors usually found on plasma membrane since signals can’t pass through membrane.

http://www.slic2.wsu.edu:82/hurlbert/micro101/images/lock_key.gif

• 1 type - G-protein-linked-receptor.

• Acts as on/off switch; cycles between being active and inactive.

• Tyrosine-kinase receptor system helps different systems to function at same time.

• System activated - activates other systems at same time.

• Ligand-gated ion channels open/close to allow chemical signals to pass through.

• Important in nervous system - allow Na+ and K+ move into and out of cell.

http://dir.niehs.nih.gov/dirln/diricp/figures/overview.jpg

• Some signals diffuse through plasma membrane; don’t need proteins.

• Some are hormones which act on transcription process.

• Transduction stage of signal pathway allows for small signal to be amplified - causes large signal.

• Protein kinases essential - help to initiate responses.

• Some involve 2nd messengers - molecules small enough to pass through membrane.

http://www.du.edu/~kinnamon/3640/second_messengers/levitan11.2.jpg

• Response of particular cell to signal depends on particular collection of proteins.

• Some pathways actually linked by scaffolding proteins - allows signals to be passed through pathways.

http://www.bnl.gov/bnlweb/pubaf/pr/photos/2004/DNAbinding-300.jpg

• All proteins involved in signal pathway important - defects in any can cause abnormal signals.