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BIO 6 - CELL COMMUNICATION 010 1. Beta cell of pancreas: a. The pancreas stores and releases insulin (and other hormones). b. A channel (facilitated diffusion down a concentration gradient) moves glucose into a beta cell. 2. CELL COMMUNICATION a. How do cells RECEIVE, PROCESS, and RESPOND to chemical signals sent from other cells? 3. CHEMICAL SIGNALING Asian army ants follow a pheromone-marked trail as they carry pupae and larvae to a new nest. 4. FIGHT OR FLIGHT RESPONSE 5. Sex, Yeast and Communication a. Yeast: single celled fungus reproduces asexually by “budding” or binary fission. b. Or sexually by “cell fusion” between different mating types. c. Binding of the factors to a cell surface receptor initiates the SIGNAL TRANSDUCTION PATHWAY. 6. Signal Transduction Pathway a. Signal transduction: The linkage of a mechanical, chemical or electromagnetic stimulus to a specific cellular response. b. Signal transduction pathway: A series of steps linking a mechanical or chemical stimulus to a specific cellular response. c. Signaling mechanisms may have first evolved in ancient prokaryotes and single-celled eukaryotes and then were adopted for use by multicellular descendants. 7. Multicellular organisms communicate by means of chemical messengers for cells local or long-distance. a. Cell junctions provide cytoplasmic channels. b. Gap junctions in animal cells consist of membrane proteins that surround a pore through which ions, sugars, amino acids, and other molecules may pass. c. Seen in many tissues including heart muscle and embryos. 8. Electron micrograph of a gap junction in an animal cell. 9. Multicellular organisms communicate by means of chemical messengers for cells next door, local or long-distance. a. Animal cells communicating by interaction between molecules protruding from their surfaces. Page 1 of 6 Beavers bio 6 STUDENT cell communication 010 10. 11. Paracrine Signaling a. Local regulator: a secreted molecule that influences cells near where it is secreted. EXAMPLE: Growth factors. b. Secretion: The discharge of molecules synthesized by a cell. c. Paracrine: referring to a secreted molecule that acts on a neighboring cell. a. b. c. d. e. 12. SIGNALING PARACRINE: Local; acts on nearby cell. AUTOCRINE: Local; secretes molecules that act on self. ENDOCRINE: Long Distance; Ductless gland secretes hormones to interstitial fluid to diffuse in the blood stream. Hormones reach all body cells but are taken in by SOME. SYNAPTIC: Found in the animal nervous system. Local and long distance. Neurotransmitters diffuse across synapses and trigger responses in cells of target tissues, neurons, muscles, glands. Neuroendocrine signaling: neurohormones diffuse into the bloodstream and trigger responses by target cells in body. Synaptic Signaling a. Nerve Cell: A neuron – the fundamental unit of the nervous system, having structure and properties that allow it to conduct signals by taking advantage of the electrical charge across its plasma membrane. b. Neurotransmitter: A molecule that is released from the synaptic terminal of a neuron at a chemical synapse, diffuses across the synaptic cleft, and binds to the postsynaptic cell, triggering a response. 13. Neuron Structure 14. Neuron Diversity 15. Page 2 of 6 Neuron Structure (Chapter 48) a. Cell body: the part of the neuron that houses the nucleus and most other organelles. b. Dendrites: One of usually numerous, short, highly branched extensions of a neuron that receive signals from other neurons. c. Axon: A typically long extension of a neuron that carries nerve impulses away from the cell body and transmits signals to other cells. d. Synapse: Each branched end of an axon transmits information to another cell at a junction called a synapse. The junction where one neuron communicates with another cell across a narrow gap. Neurotransmitter molecules released by the neuron diffuse across the synapse, relaying messages to the other cell. e. Synaptic terminal: A bulb at the end of an axon in which neurotransmitter molecules are stored and released. Beavers bio 6 STUDENT cell communication 010 16. Membrane Potential is a source of potential energy and can be called voltage or charge difference. a. ALL CELLS HAVE VOLTAGES ACROSS THEIR PLASMA MEMBRANES (CHARGE SEPARATION). b. VOLTAGE IS ELECTRICAL POTENTIAL ENERGY. c. The cytoplasm is NEGATIVE in charge in RELATION to the extracellular fluid because of an unequal distribution of anions and cations on opposite sides of the membrane. d. The difference in electrical charge (voltage) across a cell's plasma membrane, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances. e. VOLTAGE: electromotive force, or difference in electrical potential expressed in volts. f. Electromotive: producing an electric current through difference in potential g. Electromotive force: the force or electric pressure that causes a current to flow in a circuit, equivalent to the potential difference between the terminals and commonly measured in volts. 17. TWO FORCES DRIVE THE DIFFUSION OF IONS ACROSS A MEMBRANE 1. A chemical force: ion concentration gradient 2. An electrical force: effect of the membrane potential on the ions movement. Both result in the electrochemical gradient. 18. ACTION POTENTIAL (a change in membrane potential) a. Action potentials are the signals conducted by axons. b. Changes in the membrane potential occur because neurons have GATED ION CHANNELS. c. These ion channels open and close in RESPONSE TO STIMULI!! d. External stimuli: light, sound, touch, heat, smell, taste e. Internal stimuli: blood pressure, muscle tension 19. Synaptic Signaling a. Synaptic terminal: A bulb at the end of an axon in which neurotransmitter molecules are stored and released. b. Synaptic cleft: A narrow gap separating the synaptic terminal of a transmitting neuron from a receiving neuron. 20. Breakdown in synaptic cleft or reuptake of neurotransmitter by presynaptic neuron. 21. Page 3 of 6 Neurotransmitter Example: Serotonin and Prozac a. Serotonin: A neurotransmitter, synthesized from the amino acid tryptophan that functions in the central nervous system. b. Serotonin can affect sleep, mood, attention, and learning. Beavers bio 6 STUDENT cell communication 010 c. Psycho-active drug LSD binds to the brain receptors that normally bind serotonin. d. Prozac enhances the effect of serotonin by inhibiting its reuptake after release. 22. Synaptic terminals on the cell body of a post synaptic neuron. 23. Long-distance signaling: a. Hormones: In multicellular organisms, one of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the body to change their functioning. 24. THREE STAGES OF CELL SIGNALING Overview a. Step 1 is Reception: the target cell’s detection of a signaling molecule. 25. THREE STAGES OF CELL SIGNALING Overview a. Step 2 is transduction: converting the signal to a form that can bring about a specific cellular response. This can occur in a single step or in a sequence of steps called a signal transduction pathway. 26. THREE STAGES OF CELL SIGNALING Overview a. Step 3 is Response: transduced signal triggers a specific cellular response that can be any possible cellular activity. 27. EXAMPLE 28. RECEPTION a. Eaves-dropping is not a problem in cells. Only the target cell hears the intended message. b. Ligand: a molecule that specifically binds to another molecule. 29. MEMBRANE RECEPTORS: G-Protein Coupled Receptor a. G-protein: A GTP-binding protein that relays signals from a plasma membrane signal receptor to other signal transduction proteins inside the cell. b. GTP: guanosine triphosphate (similar to ATP, an energy carrying molecule). 30. 31. Cholera and the G-Protein Coupled Receptor Cholera a. Cholera bacterium Vibrio cholerae forms a biofilm that produces a toxin (actually an enzyme) that modifies the G protein. The altered G-protein cannot hydrolyze GTPGDP and remains in its active form. 32. Tyrosine Kinase Receptor 33. ION CHANNEL RECEPTORS Page 4 of 6 Beavers bio 6 STUDENT cell communication 010 a. Seen in our neuron example. 34. INTRACELLULAR RECEPTORS a. Intracellular receptors: Found in either the cytoplasm or the nucleus of target cells. b. A chemical messenger must have had the ability to pass through the target cells plasma membrane…how would that be possible? 35. XY FEMALES – Androgen Insensitivity Syndrome a. Androgen insensitivity syndrome – affected individuals are chromosomal males: 46,XY. Rare X-linked recessive phenotype. b. Incidence: 1/20,000 live births. c. Mutation in the androgen-receptor gene on the X chromosome. 36. Transduction: Cascades of Molecular Interactions Relay Signals a. Molecules that relay a signal from receptor to response are called relay molecules. 37. Cyclic AMP a. Not all components of signal transduction pathways are proteins. “Second messengers” are small, non-protein, water-soluble molecules or ions that relay a signal in response to a signaling molecule being bound b. to a receptor protein. c. They can spread readily throughout the cell by diffusion. d. Cyclic AMP (cyclic adenosine mono-phosphate, a ring shaped molecule made from ATP) is a second messenger. 38. SECOND MESSENGERS a. cAMP as a second messenger 39. CELLULAR RESPONSE a. 1. Initial signaling molecule, a local regulator called a growth factor, triggers a phosphorylation cascade. b. 2. Once phosphorylated, the last kinase in the sequence enters the nucleus and activates a gene-regulating protein – a transcription factor. c. 3. This protein stimulates a specific gene so that an mRNA is synthesized. d. 4. The mRNA directs the synthesis of a certain protein. 40. GLYCOGEN BREAKDOWN a. One signaling molecule of epinephrine stimulates release of 100 million glucose molecules by amplification. 41. CELLULAR RESPONSE: cytoplasmic regulation of the activity of proteins rather than their synthesis, directly affecting proteins that function outside of the nucleus. Page 5 of 6 Beavers bio 6 STUDENT cell communication 010 a. EXAMPLES: Opening or closing of an ion channel in the plasma membrane or change in cell metabolism. 42. Page 6 of 6 APOPTOSIS: Programmed Cell Death: an elaborate network of cell signaling. a. Apoptosis: A program of controlled cell suicide, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die. Beavers bio 6 STUDENT cell communication 010