Cell Signaling Mechanisms in Animal and Plant Cells

1. Chapter 11Cell Communication

2. Cell-Cell Communication • Animal cells use gap junctions to send signals • Cells must be in direct contact • Protein channels connecting two adjoining cells Gap junctions between animal cells

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

4. 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

5. 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

6. Three Stages of Cell Signaling • Signaling molecule binds to the receptor protein CYTOPLASM EXTRACELLULAR FLUID Plasma membrane Reception 1 1 The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!) Receptor Signaling molecule

7. Three Stages of Cell Signaling CYTOPLASM EXTRACELLULAR FLUID Plasma membrane Reception Transduction 1 1 2 Receptor 2nd Messenger! Relay molecules in a signal transduction pathway Signaling molecule • The signal is converted into a form that can produce a cellular response

8. Three Stages of Cell Signaling CYTOPLASM EXTRACELLULAR FLUID Plasma membrane Reception Transduction Response 1 2 3 Receptor Activation of cellular response Relay molecules in a signal transduction pathway Can be catalysis, activation of a gene, triggering apoptosis, almost anything! Signaling molecule • The transduced signal triggers a cellular response

9. G-Protein Receptors Inactive enzyme Plasma membrane G protein-coupled receptor Activated receptor Signaling molecule Enzyme GDP 2 1 GDP GTP CYTOPLASM G protein (inactive) Activated enzyme i GTP GDP P 4 3 Cellular response

10. Ion Channel Receptors Gate closed 1 Ions Signaling molecule (ligand) • Very important in the nervous system • Signal triggers the opening of an ion channel • depolarization • Triggered by neurotransmitters Ligand-gated ion channel receptor Plasma membrane 2 Gate open Cellular response 3 Gate closed

11. Signaling molecule Transduction: A Phosphorylation Cascade Receptor Activated relay molecule Inactive protein kinase 1 Fig. 11-9 Active protein kinase 1 Inactive protein kinase 2 ATP Phosphorylation cascade ADP P Active protein kinase 2 PP P i Inactive protein kinase 3 ATP ADP P Active protein kinase 3 PP P i Inactive protein ATP P ADP Active protein Cellular response PP P i

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

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

14. Signaling molecule • Specificity of the signal • The same signal molecule can trigger different responses • Many responses can come from one signal! Receptor Relay molecules Response 1 Response 2 Response 3 Cell A. Pathway leads to a single response. Cell B. Pathway branches, leading to two responses.

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

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