CELL SIGNALING A Gatrell interpretation.

CELLS USE SIGNALS FOR A VARITEY OF REASONS………………………..

 Single celled organisms signal to attract a “mate” or to coordinate efforts to stay alive in a harsh environment or to produce offspring. ● Yeast a/ α sexual reproduction ● Cause clumping (aggregation) to form biofilms

 Plants use simple forms of diffusion through cell junctions (plasmodesmata) for short distances but for longer distances cell walls can be a problem some signaling molecules do travel through vessels but often plants use gases that travel in the air to signal activites. ● Ethylene for fruit ripening

 Animals also use simple forms of diffusion through gap junctions ● In cells that need rapid communication like the mammalian heart  Animals also use a variety of long distance forms of communication using specialized cells which release hormone molecules, which travel via the circulatory system to the “target” cells ● Insulin released into the blood stream from the pancreas

 One very important type of signaling can be considered as both a local and long distance signal ● A neuron stimulation, even though the neurons directly touch they are capable of sending messages from the big toe to the brain. ● Quite a long distance!

SO………..  Local regulators are sometimes called growth factors and aid in cell division.  Local signaling may also be called paracrine signaling in animals.  Synaptic signaling is also considered here.

 Long distance signaling in both plants and animals is referred to as endocrine signaling and uses signaling molecules called hormones.

NOW WHAT???????  There is a chemical signal headed toward a cell membrane.  How does it respond?  Its according to if it has a receptor for the signal.  If there is NO receptor…. nothing happens, its not recognized.  If there IS a receptor…. Well, that’s another story.

A SIGNAL TRANSDUCTION PATHWAY IS INITIATED…  There are 3 main steps ● RECEPTION ● TRANSDUCTION ● RESPONSE

RECEPTION  The signaling molecule may be received by a receptor in the plasma membrane (transmembrane receptor) OR a receptor in the cytoplasm. ● The signaling molecule acts as a LIGAND, which is a molecule that specifically binds to another molecule. ● These receptors are shape specific and upon receiving the signal molecule undergo a conformational change.

TRANSDUCTION  The conformational change initiates transduction.  Transduction is a series of biochemical reactions called a signal transduction pathway.

RESPONSE  The transduced signal finally results in a “specific cellular response.” ● This results in a response from the cell often in the form of protein synthesis. ● Activation of a specific gene. ● Catalysis of an enzyme. ● Rearrangement of the cytoskeleton

OK-WE HAVE THE BASIC CONCEPT OF A SIGNAL TRANSDUCTION PATHWAY INCLUDING RECEPTION, TRANSDUCTION, AND RESPONSE.  Now, lets look at some specific examples.

RTK’S RECEPTOR TYROSINE KINASE  RTK’S are a major group of membrane receptors which have enzymatic activity.

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