Cells communicate by generating, transmitting and receiving chemical signals

1. Cells communicate by generating, transmitting and receiving chemical signals Cell communication processes share common features that reflect a shared evolutionary history

2. Communication via Transduction A signal on a cell’s surface is converted to a specific cellular response in a series of steps 1st evolved in ancient prokaryotes and single-celled eukaryotes Quorum Sensing – the concentration of signaling molecules allows a bacteria population to communicate • http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html • What did you think!??! • AMAZING – right? • This communication allows for the evolution of the bacterial species • With this communication prokaryotes have adapted and survived for millions of years!

3. Communication via Transduction In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organisms as a whole.

4. Local vs. Long-Distance Signaling • Local: • Cell junctions – substances dissolved in cytosol pass through cell to cell connection (gap junctions & plasmodesmata) • Cell-cell Recognition – interaction between molecules protruding from cell surface (i.e. immune response) • Local Regulators – signaling cells secrete messenger molecules that stimulate or inhibit nearby cells (growth factors and neurotransmitters) • Long-Distance • Endocrine signaling – specialized cells release hormones that travel through the blood stream to target cells in other parts of the body; plant regulators move through cells or diffuse through the air as a gas • Transmission signaling of the nervous system – electrochemical signals travel long distances by passing from nerve cell to nerve cell until the target cells is reached.

5. Illustrative Example: Epinephrine stimulation of glycogen breakdown in mammals Epinephrine is secreted by the adrenal gland during times of mental and physical stress. Epinephrine travels via the bloodstream to muscle cells. When epinephrine comes in contact with the cell it triggers a signal transduction pathway that activates Glycogen Phosphorylase Glycogen phophorylase then begins the breakdown of glycogen to glucose-6-phosphate which can enter glycolysis or can be modified to enter the blood stream to fuel other cells

6. Signal Transduction Pathway Reception – signal molecule detected by target cell Transduction - binding of signal molecule modifies receptor protein initiating a series of reactions that relay the message Response – signal triggers specific cellular response

7. Signaling Molecules Ligand – signal molecule that binds to receptors; the molecule that starts a signal transduction pathway Example: Insulin binds to a receptor (integral membrane protein) causing a change in the protein shape that exposes a kinase (phosphate transferring enzyme) inside a cell; the activated kinase transfers the phosphate to adjacent receptor molecules, leading to the activation of subcellular proteins and a cellular response to insulin Different receptors recognize different chemical messengers, which can be peptides, small chemicals or proteins, in a specific one-to-one relationship

8. Receptor Molecules Receptor molecules – integral membrane proteins that pass through the lipid bilayer transmit information from the extracellular environment to the inside of the cell by changing shape A receptor protein recognizes signal molecules (ligands), causing the receptor protein’s shape to change, which initiates transduction of the signal

9. G Protein-Coupled Receptors • G protein-coupled receptors work with energy rich GTP to change shape upon binding with ligand; common across many species showing evolutionary significance • Important in embryonic development and sensory reception • Key role in many human illnesses – bacterial infections interfere with G-protein function

10. Tyrosine Kinase • Tyrosine Kinases are enzymes that catalyze the phosphorylation of tyrosine • Upon activation by the ligand the kinase transfers a phosphate from ATP to tyrosine • Phosphorylation of tyrosine triggers a cascade of reactions within the cell leading to a desired response • One receptor can activate ten or more pathways / cellular response at once • Important in regulating cell growth and reproduction

11. Ion Channel Receptors • Ion channel Receptors – part of the receptor acts as a gate, blocking transfer of ions • Upon activation by the ligand the gate opens to allow the flow of specific ions • Important for the nervous system – gated ion channels on receiving cells cause channels to open allowing neurotransmitters to trigger an electrical signal (some gates controlled by electrical signals instead of ligand = voltage-gated ions channels)