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Chapter 11

Chapter 11. Cell Communication. Concept 11.1: External signals are converted into responses within the cell. Signal-transduction pathway. LE 11-2. a factor. Exchange of mating factors. Receptor. a. a. a factor. Yeast cell, mating type a. Yeast cell, mating type a. Mating.

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Chapter 11

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  1. Chapter 11 Cell Communication

  2. Concept 11.1: External signals are converted into responses within the cell • Signal-transduction pathway

  3. LE 11-2 a factor Exchange of mating factors Receptor a a a factor Yeast cell, mating type a Yeast cell, mating type a Mating a a New a/a cell a/a

  4. LE11-3 Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells Cell junctions Cell-cell recognition

  5. Local regulators - short distances • Hormones - long-distance signaling Local signaling Long-distance signaling Target cell Endocrine cell Blood vessel Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Secreting cell Secretory vesicle Hormone travels in bloodstream to target cells Local regulator diffuses through extracellular fluid Target cell Target cell is stimulated Paracrine signaling Synaptic signaling Hormonal signaling

  6. The Three Stages of Cell Signaling: A Preview Cells receiving signals go through three processes: • Reception • Transduction • Response Animation: Overview of Cell Signaling

  7. LE 11-5_1 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Receptor Signal molecule

  8. LE 11-5_2 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Receptor Relay molecules in a signal transduction pathway Signal molecule

  9. LE 11-5_3 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule

  10. Concept 11.2: Reception: A signal molecule binds to a receptor protein, causing it to change shape • Ligand • Binding is highly specific • Conformational change

  11. LE 11-6 Hormone (testosterone) EXTRACELLULAR FLUID The steroid hormone testosterone passes through the plasma membrane. Plasma membrane Testosterone binds to a receptor protein in the cytoplasm, activating it. Receptor protein Hormone- receptor complex The hormone- receptor complex enters the nucleus and binds to specific genes. DNA The bound protein stimulates the transcription of the gene into mRNA. mRNA NUCLEUS New protein The mRNA is translated into a specific protein. CYTOPLASM

  12. Receptors in the Plasma Membrane • There are three main types of membrane receptors: • G-protein-linked receptors • Receptor tyrosine kinases • Ion channel receptors

  13. LE 11-7aa Signal-binding site Segment that interacts with G proteins G-protein-linked receptor

  14. LE 11-7b Signal molecule Signal-binding site a Helix in the membrane Signal molecule Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) Dimer CYTOPLASM Activated relay proteins Cellular response 1 P P Tyr Tyr P Tyr Tyr Tyr Tyr P P P Tyr Tyr P Tyr Tyr Tyr Tyr P P P Cellular response 2 Tyr Tyr P Tyr Tyr Tyr P Tyr 6 ATP 6 ADP Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated dimer) Inactive relay proteins

  15. LE 11-7c Gate closed Signal molecule (ligand) Ions Plasma membrane Ligand-gated ion channel receptor Gate open Cellular response Gate closed

  16. Concept 11.3: Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell • Transduction usually involves multiple steps • Can amplify a signal • More opportunities for coordination and regulation

  17. LE 11-8 Signal molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP ADP P Active protein kinase 2 Phosphorylation cascade PP P i Inactive protein kinase 3 ATP ADP P Active protein kinase 3 PP P i Inactive protein ATP P ADP Cellular response Active protein PP P i

  18. Small Molecules and Ions as Second Messengers First messenger (signal molecule such as epinephrine) Adenylyl cyclase • Second messengers are small, nonprotein, water-soluble molecules or ions • Cyclic AMP (cAMP) G protein G-protein-linked receptor GTP ATP Second messenger cAMP Protein kinase A Cellular responses

  19. LE 11-10 First messenger (signal molecule such as epinephrine) Adenylyl cyclase G protein G-protein-linked receptor GTP ATP Second messenger cAMP Protein kinase A Cellular responses

  20. Calcium ions and Inositol Triphosphate (IP3) EXTRACELLULAR FLUID Plasma membrane Ca2+ pump • Calcium ions (Ca2+) act as a second messenger in many pathways ATP Mitochondrion Nucleus CYTOSOL Ca2+ pump Endoplasmic reticulum (ER) ATP Ca2+ pump Low [Ca2+] High [Ca2+] Key

  21. Concept 11.4: Response: Cell signaling leads to regulation of cytoplasmic activities or transcription • “output response” • cytoplasm • nucleus • Many pathways regulate the activity of enzymes

  22. LE 11-13 Reception Binding of epinephrine to G-protein-linked receptor (1 molecule) Transduction Inactive G protein Active G protein (102 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (102) ATP Cyclic AMP (104) Inactive protein kinase A Active protein kinase A (104) Inactive phosphorylase kinase Active phosphorylase kinase (105) Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response Glycogen Glucose-1-phosphate (108 molecules)

  23. Growth factor Reception Receptor • Transcription factor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor Response P DNA Gene NUCLEUS mRNA

  24. Signaling Efficiency: Scaffolding Proteins and Signaling Complexes • Scaffolding proteins can increase the signal transduction efficiency Signal molecule Plasma membrane Receptor Three different protein kinases Scaffolding protein

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