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CH11 Cell Communication

CH11 Cell Communication

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CH11 Cell Communication

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  1. CH11 Cell Communication

  2. VOCABULARYdirections: mark each term to indicate if you know it, are unsure, or don’t. amplify communication deleterious elaborate embryology evolution fluid mosaic model mechanism phosphorylation prophylactic regulation response signaling signal molecule specify second messengers signal transduction quorum sensing IP3 G protein QUESTIONS generate a list to be answered today Who What Where When Which How Why

  3. communication You know it is important. What does it mean? Brainstorm words related to “communication”.

  4. Where on the cell does the “communication” occur? • “speaking” occurs through the production and release of LIGANDS hormones or other chemical messengers using the cells machinery, vesicles, and exocytosis. • “Listening” occurs by receptor proteins embedded in the cell membrane and by way of signal transduction pathways (domino effect of sorts) . • “Reacting” occurs when specific enzymes become activated (because of the signal transduction pathway) and the cell performs a specific function.

  5. How do cells communicate? They are a lot like you… they use many different methods for communicating and their “messages” can result in a variety of responses. Process info via SIGNAL TRANSDUCTION PATHWAY

  6. COMMUNICATIONTalking, listening, & responding. Cells communicate by generating, transmitting and receiving chemical signals.

  7. Big Idea 3:Living systems store, retrieve, transmit and respond to information essential to life processes. Big Idea 1:The process of evolution drives the diversity and unity of life.

  8. The expression of genetic material controls cell products, and these products determine the metabolism and nature of the cell. 1) Gene expression is regulated by both • 1)environmental signals and • 2)developmental cascades or stages. 2) Cell signaling mechanisms can also modulate and control gene expression. 3) Structure and Function in biology involve two interacting aspects: • 1) the presence of necessary genetic information and • 2) the correct and timely expression of this information.

  9. Cell communication processes share common features that reflect a shared evolutionary history. • Communication involves transduction of stimulatory or inhibitory signals from other cells, organisms or the environment. • Correct and appropriate signal transduction processes are generally under strong selective pressure. • In single-celled organisms, signal transduction pathways influence how the cell responds to its environment. Examples: • Use of chemical messengers by microbes to communicate with other nearby cells and to regulate specific pathways in response to population density (quorum sensing) • Use of pheromones to trigger reproduction and developmental pathways • Response to external signals by bacteria that influences cell movement

  10. 1 2 3 Communication among bacteria QUORUM SENSING- bacteria Can sense changes in density And act appropriately. Individualrod-shapedcells Figure 11.3 Aggregation in progress 0.5 mm Spore-formingstructure(fruiting body) 2.5 mm Fruiting bodies

  11. 1 Figure 11.3a Individual rod-shaped cells

  12. 2 Figure 11.3b Aggregation in progress

  13. 3 0.5 mm Figure 11.3c Spore-forming structure(fruiting body)

  14. 2.5 mm Figure 11.3d Fruiting bodies

  15. A variety of intercellular and intracellular signal transmissions mediate gene expression. a. Signal transmission within and between cells mediates gene expression. b. EXAMPLES: • Cytokines regulate gene expression to allow for cell replication and division. YEAST • Mating pheromones trigger mating gene expression in yeast. BACTERIA • Levels of cAMP regulate metabolic gene expression in bacteria. PLANTS • Ethylene (hormone) levels cause changes in the production of different enzymes, allowing fruits to ripen. • Gibberellin (hormone) causes seed germination. ANIMALS • Expression of the SRY gene triggers the male sexual development pathway in animals.

  16. Signals come from cells or changes in their physical environment: • Chemicals (pheromones, hormones) • Light electromagnetic radiation, touch, gravity • Receptors are proteins embedded in the cell membrane. • Signal transduction pathways relay signals from receptors to cellular responses. • Responses include: specific enzyme activation • Inhibitory response (via inhibitors) • Excitatory response (via activators- coenzyme or cofactor)

  17. Why do cells need to communicate? • (unicellular) To be able to survive and reproduce • Find food and water • Escape/avoid danger • Find mates • (multicellular) To develop from a fertilized egg. • Differentiation • Programmed cell death (Apoptosis)

  18. Effect of apoptosis during paw development in the mouse. Figure 11.22 Cells undergoingapoptosis Space betweendigits 1 mm Interdigital tissue Ex.Morphogens stimulate cell differentiation and development.

  19. Apoptosis of a human white blood cell. Figure 11.20 2 m Once it engulfs bacteria it commits “cell suicide” by carefully packaging its contents into multiple vesicles (membrane bound bags).

  20. How does cell signaling trigger the desperate flight of this gazelle? Have you ever been scared? What does your body do? Figure 11.1

  21. The “fight or flight” response is signaled by the hormone epinepherine or adrenaline. • Causes changes to maximize ATP production • the release of glucose from muscles and liver cells • Increase in respiration depth and rate • Increase in heart rate

  22. Reception Binding of epinephrine to G protein-coupled receptor (1 molecule) Transduction Inactive G protein Active G protein (102 molecules) Figure 11.16 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) Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrine.

  23. How is communication different btwn single and multicellular organisms? • In single-celled organisms, signal transduction pathways influence how the cell responds to its environment. whereas • In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole. • Temperature determination of sex in some vertebrate organisms • DNA repair mechanisms • Epinephrine stimulation of glycogen breakdown in mammals

  24. How is communication different in multicellular organisms? • In multicellular organisms, cell-to-cell and environment-to-cell chemical signaling pathways direct complex processes. • Ex. cell and organ differentiation to whole organism physiological responses and behaviors. • Certain signal pathways involve direct cell-to-cell contact, operate over very short distances, and may be determined by the structure of the organism or organelle, including • plasmodesmata in plants and • receptor-to-recognition protein interaction in the vertebrate immune system.

  25. Plasma membranes Figure 11.4 Gap junctionsbetween animal cells Plasmodesmatabetween plant cells (a) Cell junctions Communication by direct contact between cells. (b) Cell-cell recognition

  26. Which life forms use cell communication? • Cell-to-cell communication is ubiquitous in biological systems, from archaea and bacteria to multicellular organisms. • The basic chemical processes by which cells communicate are shared across evolutionary lines of descent, and communication schemes are the products of evolution. • For cells to function in a biological system, they must communicate with other cells and respond to their external environment.

  27. When did cell communication evolve? • Cell-to-cell communication is a component of higher-order biological organization and responses. • Communication evolved billions of years ago among the most ancient bacteria.

  28. OVERVIEW: 1) Cell communication evolved early in the history oflife. • Cell-to-cell communication is essential for multicellular organisms. The trillions of cells in a human or an oak tree must communicate in order to develop from a fertilized egg. • Additional evidence for the evolutionary relatedness of all life comes from discovering some universal mechanisms of cellular regulation. • Q: What molecular evidence suggests the unity of life on Earth (descent from a common ancestor)?

  29. Knowledge of cell signaling mechanisms are answering questions in medicine and biology in these areas: embryological development, hormone action, cancer. • Ex. Changes in p53 activity can result in cancer. • Examples of signals that can be received by cells and the possible responses: • Changes in light duration lead to changes in plants (dropping leaves, flowering) • Light & phototropism (plant cell growth toward light) • Gravity or touch effects plant growth (shoots away from gravity, roots toward gravity)

  30. b. Signal transmission within and between cells mediates cell function. • Main topic of cell “conversation” = SEX… • Ex. YEAST Saccharomycescerevisiae • Mating pheromones in yeast trigger mating genes expression and sexual reproduction. • Q: How is the mating signal at the yeast cell surface “transduced”, or changed, into a form that brings about the cellular response of mating? • A: Signal Transduction Pathway

  31. 1 2 3  factor Receptor 2 mating types Each secretes A mating factor That binds to the other Cell. Exchange of mating factors a  a factor Figure 11.2 Yeast cell, mating type a Yeast cell, mating type  Mating a  New a/ cell a/ Communication between mating yeast cells.

  32. Scientists think signaling mechanisms evolved first in ancient prokaryotes and single celled eukaryotes and were then adopted for new uses by their multicellular descendants.

  33. Local and long-distance cell signaling by secreted molecules in animals. 2) Communicating cells can be close together or far apart. Local signaling Long-distance signaling Target cell Electrical signalalong nerve celltriggers release ofneurotransmitter. Endocrine cell Bloodvessel Figure 11.5 Neurotransmitter diffuses across synapse. Secretingcell Secretoryvesicle Hormone travelsin bloodstream. Target cellspecificallybinds hormone. Local regulatordiffuses throughextracellular fluid. Target cellis stimulated. (a) Paracrine signaling (b) Synaptic signaling (c) Endocrine (hormonal) signaling • Local signaling: paracrine or synaptic involves…secreting molecules short distances. Ex. neurotransmitters. • Long distance (hormonal) signaling… secretes hormones for signaling at greater distances. Known as ENDOCRINE signaling.

  34. 3 2 1 3) The 3 stages of cell signaling: EXTRACELLULARFLUID CYTOPLASM Plasma membrane Figure 11.6-3 Response Reception Transduction Receptor Activationof cellularresponse Relay molecules in a signal transductionpathway Signalingmolecule #1 reception: ligand binding to receptor #2 transduction: relay molecules employed #3 response: activation of cellular response


  36. RECEPTION & THE INITIATION OF TRANSDUCTION Signal transduction pathways link signal reception with cellular response. • 1) Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein. • Different receptors recognize different chemical messengers, which can be • peptides, • small chemicals or • proteins, in a specific one-to-one relationship.

  37. 2)A receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, • which initiates transduction of the signal. • Examples:  • G-protein linked receptors • Receptor tyrosine kinases • Ligand-gated ion channels • The Exception: Non-membrane protein receptors

  38. G-protein linked receptor Signaling molecule binding site Figure 11.7a Segment thatinteracts with G proteins G protein-coupled receptor

  39. 1 2 4 3 G-protein linked receptors G protein-coupledreceptor Plasmamembrane Activatedreceptor Signalingmolecule Inactiveenzyme Figure 11.7b GTP GDP GDP CYTOPLASM Enzyme G protein(inactive) GTP GDP Activatedenzyme GTP GDP P i Cellular response Explain in in your own words what is happening during steps 1-4.

  40. RECEPTOR TYROSINE KINASES Explain steps 1-4 in your own words. 2 1 3 4 Signalingmolecule (ligand) Ligand-binding site Signalingmolecule  helix in themembrane Tyr Tyr Tyr Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Figure 11.7c Tyr Tyr Tyr Tyr Tyr Tyr CYTOPLASM Receptor tyrosinekinase proteins(inactive monomers) Dimer Activated relayproteins Cellularresponse 1 P Tyr P Tyr P Tyr Tyr Tyr Tyr P Tyr P Tyr P P Tyr Tyr Tyr Tyr P Cellularresponse 2 Tyr P Tyr P Tyr Tyr P Tyr Tyr P 6 ADP 6 ATP Fully activatedreceptor tyrosinekinase(phosphorylateddimer) Activated tyrosinekinase regions(unphosphorylateddimer) Inactiverelay proteins

  41. 2 1 3 LIGAND GATED ION CHANNELS Explain steps 1-3 in your own words. Figure 11.7d Gate closed Gate closed Ions Gate open Signalingmolecule (ligand) Plasmamembrane Ligand-gatedion channel receptor Cellularresponse Cellular response ex. Muscle Cell contractions.

  42. EXTRACELLULARFLUID Hormone(testosterone) The exceptions: Non membrane protein Receptors Are found in the cytoplasm. are activated by Steroid hormones. Activate transcription Factors in the nucleus. Plasmamembrane Receptorprotein Figure 11.9-1 DNA NUCLEUS CYTOPLASM

  43. EXTRACELLULARFLUID Hormone(testosterone) The exceptions: Non membrane protein Receptors Are found in the cytoplasm. are activated by Steroid hormones. Activate transcription Factors in the nucleus. Plasmamembrane Receptorprotein Why is is that steroid Hormones can pass Through the cell membrane? Figure 11.9-2 Hormone-receptorcomplex DNA NUCLEUS CYTOPLASM

  44. EXTRACELLULARFLUID Hormone(testosterone) The exceptions: Non membrane protein Receptors Are found in the cytoplasm. are activated by Steroid hormones. Activate transcription Factors in the nucleus. Plasmamembrane Receptorprotein Figure 11.9-3 Hormone-receptorcomplex And nuclear envelope? DNA NUCLEUS CYTOPLASM

  45. EXTRACELLULARFLUID Hormone(testosterone) The exceptions: Non membrane protein Receptors Are found in the cytoplasm. are activated by Steroid hormones. Activate transcription Factors in the nucleus. Plasmamembrane Receptorprotein Figure 11.9-4 Hormone-receptorcomplex Steroids are lipids. Like dissolves like. Are not repelled by the Hydrophobic tails of the Phospholipidbilayer. DNA mRNA NUCLEUS CYTOPLASM

  46. EXTRACELLULARFLUID Hormone(testosterone) The exceptions: Non membrane protein Receptors Are found in the cytoplasm. are activated by Steroid hormones. Activate transcription Factors in the nucleus. Plasmamembrane Receptorprotein Figure 11.9-5 Hormone-receptorcomplex DNA mRNA NUCLEUS New protein CYTOPLASM

  47. SIGNAL TRANSDUCTION PATHWAYS •  1) Signal transduction is the process by which a signal is converted to a cellular response.

  48. CELLULAR RESPONSES TO SIGNALS 1) In response to a signal, a cell may regulate activities in the cytoplasm or transcription in the nucleus. 2) Elaborate pathways amplify and specify the cells response to signals. • Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals, with the result of appropriate responses by the cell. • Second messengers are often essential to the function of the cascade. • Examples of second messengers: • Cyclic AMP cAMP • inositoltriphosphate IP3

  49. Figure 11.11 Adenylyl cyclase Phosphodiesterase Pyrophosphate H2O P i P ATP cAMP AMP Why is the molecule called “cyclic” AMP not just AMP?

  50. First messenger(signaling moleculesuch as epinephrine) Adenylylcyclase 1st messenger? 2nd messenger? G protein Figure 11.12 GTP G protein-coupledreceptor ATP Second messenger cAMP Proteinkinase A Cellular responses