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28 Cards in this Set
- Front
- Back
Signal transduction pathway
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Series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response.
1.Evolved in ancient prokaryotes and early single-celled eukaryotes. 2.Later adapted for use by multicellular organisms. 3. Example:Mating yeast cells. |
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Local and Long Distance Signaling
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1. Locally, cells can communicate through junctions that directly connect adjacent cells.
2. Signaling substances dissolved in the cytosol can pass easily between adjacent cells. 3. Animal cells can communicate by direct contact between membrane-bound cell surface molecules (cell-to-cell recognition). |
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Local regulator
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Secreted molecule that influences cells near where it is secreted.
a)Growth factors (paracrine signaling). b)Synaptic signaling. |
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Hormones
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Type of secreted molecule formed in specialized cells; travels throughout the body in fluids, acting on specific cells, influencing change in target cells (long distance).
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Hormones
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Plant hormones travel through vessels or diffuse through cells and air
Animal hormones are restricted largely to vessels Hormones vary widely in size and type: Ethylene – promotes fruit ripening, regulates growth = 6 atoms Insulin – regulates blood-sugar levels = 1,000’s of atoms |
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Cell Signaling
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In the case of epinephrine’s effect on the body, epinephrine is secreted from the adrenal gland during times of physical or mental stress resulting in the mobilization of fuel reserves. Glycogen to glucose to respiration
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Three stages of cell signaling
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Stage 1: Reception
Stage 2: Transduction Stage 3: Response |
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Stage 1: Reception
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The target cell detects an external signaling molecule when the molecule binds to a receptor protein on the cell’s surface or inside the cell.
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Stage 2: Transduction
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The signal carried by the molecule is converted by the cell to bring about a specific response – sometimes in a single step, but more often in a series of steps.
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Stage 3: Response
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Transduced signal triggers a specific response – enzyme activity, rearrangement of the cytoskeleton, or activation of specific genes – at the right time and in coordination with other cellular activities.
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Receptor Proteins
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A receptor protein on or in a target cell allows the cell to receive and respond to the signal. The signaling molecule is complementary in shape to a specific site on the receptor and will react only with the target cell.
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Ligand
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Signaling molecule that binds specifically to another receptor molecule – usually a larger one.
a) Causes protein receptor to change shape. b) Receptor is activated, reacting with other cellular molecules or aggregating with other receptors. c) Results in further molecular events |
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G Protein-coupled Receptors
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Signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activation a G protein.
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Properties of G Protein-coupled Receptors
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a) GTP = energy-rich molecule.
b) Receptors are wide-spread. c) Function: sensory reception. d) Bacterial infections interfere with proper function. |
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Receptor Tyrosine Kinases
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Receptor protein spanning the plasma membrane, the cytoplasmic part of which can catalyze the transfer of a phosphate group from ATP to tyrosine
a) Respond to ligands. b) Activates the signal transduction proteins within the cell. c) Abnormal function = cancer. |
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Ligand-gated Ion Channel
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Trans membrane protein containing a pore that opens or closes as it changes shape in response to signaling molecules; regulating ion flow.
a) Example: neurotransmitters. b) Function: nervous reception, transmission. |
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Intracellular Receptors
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1. Intracellular receptor proteins are found either in-side the cytoplasm or on the nucleus.
2. Signaling molecule passes through the plasma membrane – being either hydrophobic or small enough to pass through. 3. Activation occurs upon binding of signaling molecule to target cell receptor. |
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Signal Transduction Pathways
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The binding of a specific signaling molecule to a receptor in the plasma membrane triggers the first step in a chain of molecular interactions that leads to a particular response within the cell. Transduction stage usually consists of multiple steps
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Signal Transduction Pathways- Multiple steps
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a) Results in signal amplification.
b) Larger number of activated molecules. c) More opportunities for coordination and regulation. (e.g.Protein phosphorylation and dephosphorylation, Cyclic AMP, Calcium ions and Inositol triphosphate (IP3)). |
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Second Messenger
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Small, non-protein, water-soluble molecule or ion (calcium ion, cyclic AMP), that relays a signal to a cell’s in-terior in response to a signaling molecule bound by a signal receptor protein.
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Nuclear and Cytoplasmic Responses
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1. Genes may be turned on or off as in the case of
protein synthesis. 2.Protein activity may be regulated, directly affecting proteins outside the nucleus as in the case of enzyme function. 3. Signaling pathways may regulate the activity of proteins rather than their synthesis. 4. Liver cells respond to epinephrine by regulating cellular energy metabolism by affecting the activity of an enzyme which catalyzes the breakdown of glycogen into glucose 5. Response may affect cell shape. 6. Nonmotile yeast mate by the growth of localized projections in one cell toward the opposite mating type. |
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Signal Amplification
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a) Elaborate enzyme cascades amplify the cell’s response to a signal.
b) At each catalytic step in the cascade, the number of activated products is much greater than in the preceding step. c) For instance, a small number of epinephrine molecules can lead to the release of hundreds of millions of glucose molecules from glycogen. |
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Specificity and Coordination of the Response
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a) Different kinds of cells turn on different genes resulting in different kinds of cells possessing different collections of proteins.
b) Two different cells can respond differently to the same signal (heart & liver cells to epinephrine). c) Economical to use some of the same proteins in more than one pathway. |
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Scaffolding proteins
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Type of large relay protein to which several other relay proteins are simultaneously attached, increasing the efficiency of signal transduction.
1. Enhances speed and accuracy of signal transfer between cells due to structure alignment. 2. May more directly activate other relay proteins |
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Termination of the Signal
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a) The ability of the cell to receive new signals depends on reversibility of the changes produced by prior signals.
b) Each molecular change must last only a short time, resulting in the cell’s readiness to respond to a fresh signal. |
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Apoptosis
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Type of programmed cell death which is brought about by activation of enzymes that break down many chemical components in the cell.
1. DNA and other cellular components are fragmented. 2. Cell shrinks and becomes lobe-shaped. 3. Cell’s parts are packaged in vesicles and engulfed and digested by scavenger cells. |
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Apoptotic Pathways and Signals
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1. Mitochondrial proteins are triggered to form molecular pores in the mitochondrial membrane causing it to leak and release other proteins that promote apoptosis.
2. When a death-signaling molecule, which was presumably released by a neighboring cell, occupies a cell surface receptor, it activates caspases and other enzymes that carry out apoptosis (no mitochondria). |
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Caspases
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Family of proteins that are one of the main executors of the apoptotic process; they form active enzymes following the induction of apoptosis.
-Signals may originate from the nucleus, generated when the DNA has suffered irreparable damage. -Signals may also originate from the endoplasmic reticulum when excessive protein misfolding occurs. -In vertebrates, apoptosis is essential in:. a) Normal development of the nervous system. b) Normal operation of the immune system. c) Morphogenesis of hands and feet. -In humans, apoptosis may be responsible for: a) Parkinson’s and Alzheimer’s disease. b) Cancer due to the failure of apoptosis to occur. |