Cell Communication Lecture 4 Fall 2008

How do cells communicate? 1 Quorum sensing, biofilm formation Fig. 11.3

How do cells communicate? 2 Signal Transduction Pathways A mechanism linking a mechanical or chemical stimulus to a specific cellular response Quorum sensing, biofilm formation Fig. 11.2

Local and Long Distance Signaling: An Overview 3 Local signaling – direct contact Cell junctions connect cytoplasm Cell-cell recognition Interactions between cell surface molecules (e.g. glycoproteins, glycolipids) Fig. 11.4

Local and Long Distance Signaling: An Overview 4 Local signaling – messenger molecules Local regulators Messenger molecules that travel only a short distance Paracrine signaling Discharge of local regulators by one cell (secreting cell) Acts on cells nearby Synaptic signaling Release of neurotransmitter molecules from a nerve cell to a target cell Fig. 11.5 Fig. 6.21

Local and Long Distance Signaling: An Overview 5 Long distance signaling Endocrine signaling Hormones released into bloodstream Travel to target cell Fig. 11.5

Overview of Cell Signaling 6 Overview of Cell Signaling Three stages Reception Transduction Response Target cell detects signaling molecule Signaling molecule binds to receptor protein Cell surface Inside cell Fig. 11.6

Overview of Cell Signaling 7 Transduction Conversion of signal to a form that can bring about a cellular response May be several steps with intermediaries: signal transduction pathway relay molecules Response Fig. 11.6

Reception High specificity Receptor proteins Ligand On plasma membrane 8 High specificity Receptor proteins On plasma membrane G protein coupled receptors Receptor tyrosine kinases Ion channel receptors Inside cell Ligand A molecule that binds specifically with another molecule

Transduction Signal Transduction Pathways 9 Transduction Signal Transduction Pathways A mechanism linking a mechanical or chemical stimulus to a specific cellular response Reception of signal by receptor protein on plasma membrane

Signal Transduction Pathways 10 Phosphorylation activates a protein Phosphate group is transferred from ATP (adenosine triphosphate) to the protein Protein changes conformation Relay molecules often protein kinases Protein that transfers phosphate groups from ATP to another protein Fig. 11.9

Signal Transduction Pathways 11 Phosphorylation cascade a series of different molecules in a pathway are phosphorylated in turn, and add phosphate group to next molecule in pathway Dephosphorylation returns protein to inactive form Protein phosphatases enzymes that rapidly remove phosphate groups from a protein Turns off / resets the pathway Fig. 11.9

Response Occurs in nucleus or cytoplasm Response in nucleus 12 Occurs in nucleus or cytoplasm Response in nucleus Often protein synthesis Activates transcription factor to turn gene “on” (or off) Start/stop transcription of RNA from DNA Fig. 11.14

Response Response in cytoplasm 13 Response in cytoplasm E.g., breakdown of glycogen into glucose Fig. 11.15

Signal Amplification 14 At each step in the cascade, the number of activated products is greater than the proceeding step Proteins remain in activated form long enough to process many other molecules before becoming inactive A few epinephine molecules leads to release of hundreds of millions of glucose molecules from glycogen Fig. 11.15

Transduction when using Intracellular Receptors 15 Intracellular receptor proteins Cytoplasm Nucleus Signal molecule must cross plasma membrane Hydrophobic or small E.g., steroids hormones, thyroid hormones

Transduction when using Intracellular Receptors 16 Fig. 11.8 Signal molecule binds with receptor protein in cell Becomes active Receptor protein often a transcription factor, or activates a transcription factor Start/stop transcription of RNA from DNA Results in protein synthesis

Specificity of Cell Signaling 17 Response of a cell to a signal depends on the type of proteins found in the target cell Fig. 11.17

Signal Transduction in Yeast 18 How do yeast grow towards each other? Read Fig. 11.16 Inquiry: How do signals induce directional cell growth in yeast. Focus on methodology. Fig. 11.16 1. Mating factor activates receptor 2. G protein binds GTP and becomes activated 3. Phosphoylation cascade activates Fus3, which moves to plasma membrane 4. Fus 3 phophorylates formin, activating it Formin initiaes growth of microfiliments Shmoo projections form Fig. 11.2