1. AP Biology Chapter 11 Cell Communication

2. AP Biology The Cellular “Internet”  Within multicellular organisms, cells must communicate with one another to coordinate their activities  A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response  Signal transduction pathways are very similar in all organisms, even organisms as different as unicellular yeasts and multicellular mammals

3. AP Biology Communication Methods  Cell-to-cell contact  Local signaling  Long distance signaling

4. AP Biology Cell-to-Cell Communications  Cell (gap) junctions must directly connect the cytoplasm of adjacent cells; Protein channels connecting two adjoining cells  Animal cells use gap junctions to send signals  Ex: cardiac cells for rhythmicity;  Surface receptors can give/send information  Ex: specific immune response Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells VIDEO

5. AP Biology Cell-Cell Communication Plasmodesmata between plant cells  Plant cells use plasmodesmata to send signals  Cells must be in direct contact  Gaps in the cell wall connecting the two adjoining cells together

6. AP Biology Local Signaling  Other types of signaling over a short distance  Cell-cell recognition  Membrane bound cell surface molecules  Glycoproteins  Glyolipids  Local regulators  Growth factors  Only work over a short distance

7. AP Biology Long-Distance Signaling  Nervous System in Animals  Electrical signals through neurons  Endocrine System in Animals  Uses hormones to transmit messages over long distances  Plants also use hormones  Some transported through vascular system  Others are released into the air

8. AP Biology Local/Long-Distance Signaling  Messenger molecules can also be secreted by the signaling cell  Paracrine signaling:  One cell secretes (releases) molecules that act on nearby “target” cells  Example: growth factors  Synaptic Signaling:  Nerve cells release chemical messengers (neurotransmitters) that stimulate the target cell

9. AP Biology Long-Distance Signaling  Endocrine (hormone) signaling  Specialized cells release hormone molecules, which travel (usually by diffusion through cells or through the circulatory system) to target cells elsewhere in the organism

10. AP Biology The Three Stages of Cell Signaling  There are 3 stages at the “receiving end” of a cellular conversation: 1. Reception 2. Transduction 3. Response

11. AP Biology Reception 1 EXTRACELLULAR FLUID Receptor Signaling molecule Plasma membrane CYTOPLASM 1 Step One - Reception  Signaling molecule (ligand) binds to the receptor protein The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!)

12. AP Biology Step 1: Reception  The target cell “detects” that there is a signal molecule coming from outside the cell  The signal is detected when it binds to a protein on the cell’s surface or inside the cell  The signal molecule “searches out” specific receptor proteins  The signal molecule is a ligand  It is a molecule that specifically binds to another one (think enzymes!)

13. AP Biology Step Two - Transduction Reception 1 EXTRACELLULAR FLUID Receptor Signaling molecule Plasma membrane CYTOPLASM 1 Relay molecules in a signal transduction pathway Transduction 2  The signal is converted into a form that can produce a cellular response 2 nd Messenger!

14. AP Biology Step 2: Transduction  This stage converts the signal into a form that can bring about a specific cellular response  One signal-activated receptor activates another protein, which activates another molecule, etc., etc.  These act as relay molecules  Often the message is transferred using protein kinases, which transfer phosphate groups from ATP molecules to proteins

15. AP Biology Signal molecule Active protein kinase 1 Active protein kinase 2 Active protein kinase 3 Inactive protein kinase 1 Inactive protein kinase 2 Inactive protein kinase 3 Inactive protein Active protein Cellular response Receptor P P P ATP ADP ATP PP Activated relay molecule i Phosphorylation cascade P P i i P  Step 2 – Transduction (phosphorylation cascade) Figure 11.8 A relay molecule activates protein kinase 1. 1 2 Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. Active protein kinase 2 then catalyzes the phos- phorylation (and activation) of protein kinase 3. 3 Finally, active protein kinase 3 phosphorylates a protein (pink) that brings about the cell’s response to the signal. 4 Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse. 5

16. AP Biology EXTRACELLULAR FLUID Plasma membrane CYTOPLASM Receptor Signaling molecule Relay molecules in a signal transduction pathway Activation of cellular response Reception TransductionResponse 1 2 3 Step Three - Response  The transduced signal triggers a cellular response Can be catalysis, activation of a gene, triggering apoptosis, almost anything!

17. AP Biology Step 3: Response  The signal that was passed through the signal transduction pathway triggers a specific cellular response  Examples: enzyme action, cytoskeleton rearrangement, activation of genes, etc., etc.  Diagram example: transcription of mRNA

18. AP Biology The Specificity of Cell Signaling  The particular proteins that a cell possesses determine which signal molecules it will respond to and how it will respond to them  Liver cells and heart cells, for example, do not respond in the same way to epinephrine because they have different collections of proteins

19. AP Biology  There are three main types of plasma membrane receptors:  G-protein-linked  Tyrosine kinases  Ion channel Types of Receptors

20. AP Biology G-protein-linked receptors  Very common  Results in a single pathway response G-protein-linked Receptor Plasma Membrane Enzyme G-protein (inactive) CYTOPLASM Cellular response Activated enzyme Activated Receptor Signal molecule Inactivate enzyme GDP GTP P iP i GDP

21. AP Biology Receptor tyrosine kinases  Multiple pathway response Signal molecule Signal-binding site CYTOPLASM Tyrosines Signal molecule  Helix in the Membrane Tyr Dimer Receptor tyrosine kinase proteins (inactive monomers) P P P P P P Tyr P P P P P P Cellular response 1 Inactive relay proteins Activated relay proteins Cellular response 2 Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated dimer) 6 ATP 6 ADP Figure 11.7

22. AP Biology Signaling molecule (ligand) Gate closed Ions Ligand-gated ion channel receptor Plasma membrane Gate open Cellular response Gate closed 1 2 3 Ion Channel Receptors  Very important in the nervous system  When ligand binds, channel can open or close.  depolarization  Triggered by neurotransmitters

23. AP Biology Hormone (testosterone) EXTRACELLULAR FLUID Receptor protein DNA mRNA NUCLEUS CYTOPLASM Plasma membrane Hormone- receptor complex New protein Figure 11.6 *Intracellular Receptors  Target protein is INSIDE the cell  Must be hydrophobic molecule 1 The steroid hormone testosterone passes through the plasma membrane. The bound protein stimulates the transcription of the gene into mRNA. 4 The mRNA is translated into a specific protein. 5 Testosterone binds to a receptor protein in the cytoplasm, activating it. 2 The hormone- receptor complex enters the nucleus and binds to specific genes. 3 Why can the signal molecule meet its target INSIDE the cell?

24. AP Biology First messenger Fig. 11-11 G protein Adenylyl cyclase GTP ATP cAMP Second messenger Protein kinase A G protein-coupled receptor Cellular responses Transduction in a G-protein pathway

25. AP Biology Response  Many possible outcomes  This example shows a transcription response Growth factor Receptor Phosphorylation cascade Reception Transduction Active transcription factor Response P Inactive transcription factor CYTOPLASM DNA NUCLEUS mRNA Gene

26. AP Biology  The signal can also trigger an activator or inhibitor  The signal can also trigger multiple receptors and different responses Response 4Response 5 Activation or inhibition Cell C. Cross-talk occurs between two pathways. Cell D. Different receptor leads to a different response.

27. AP Biology Yeast Sexual Reproduction  factor Receptor Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. 1 Mating. Binding of the factors to receptors induces changes in the cells that lead to their fusion. New a/  cell. The nucleus of the fused cell includes all the genes from the a and a cells. 2 3  factor Yeast cell, mating type a Yeast cell, mating type    a/  a a Yeast cells identify their mates by cell signaling.

28. AP Biology Evolutionary Significance  Unicellular and multicellular cell communication have similarities  Yeast cells signal for sexual reproduction through signal transduction process.  Bacteria secrete molecules to sense density of own population.  Quorum Sensing (survival purpose) TEDED on Quorum Sensing