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103 Cards in this Set
- Front
- Back
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a and alpha |
Different sexes of cell Each type secretes a specific receptor that binds only to receptors on the other cell They then fuse |
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Signal transduction pathway |
The binding of a mating factor at each cell initiates a series of steps |
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Ancestral signaling |
Likely evolved in prokaryotes and single celled eukaryote |
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Cell signaling is critical among |
Prokaryotes |
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Quorum sensing |
A concentration of signaling molecules allows bacteria to sense local population density or: biofilm (aggregation of bacterial cells) |
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Staphylococcus aureus |
When this bacteria enters tissue, it secretes a toxin killing body cells and contributing to inflammation Interfering with the signaling pathway used in quorum sensing may be an approach as an alternative to tx resistant bacteria |
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How cells in a multicellular organism communicate |
Signaling molecules |
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In local signaling |
Animal cells communicate by direct contact |
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Cell junctions |
Connect directly via cytoplasm of adjacent cells |
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Paracrine signaling |
Local Secrete messenger molecules that travel short distances Growth factors stimulate nearby target cells to grow and divide |
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Growth factors |
Nearby compounds that stimulate nearby target cells to grow and divide |
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Synaptic signaling |
Local and Occurs in nervous system Electrical signal travels the neuron to secrete NTs Travel across the synapse triggering a response |
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Local signaling in plants occurs btw |
Plasmodesmata |
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Used in long distance signaling... |
Hormones |
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Endocrine signaling |
Long distance signaling Travel the circulatory system to their parts of the body |
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Plant growth regulators |
Plant hormones travel in plant vesicles or moving through cells by diffusing through the air |
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Plant hormone ethylene |
A gas that promotes fruit ripening and regulates growth Hydrocarbon so capable of passing through cell walls |
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Mammalian hormone insulin |
Regulates blood sugar levels in mammals A protein with a thousand atoms |
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Transmission is a signal through the nervous system |
Electrical signal travels the length of a nerve cell-> Converts to a chemical—> Signaling molecule is released and crosses the synapse to another nerve cell—> Converted back to an electrical signal |
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What happens when a nerve cell encounters a secreted signaling molecule? |
The signal must be recognized and bound by a specific receptor molecule which must be changed inside the cell for cell response |
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3 stages of cell signaling |
Reception Transduction Response |
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Earl Sutherland |
Discovered how epinephrine still mates the breakdown of the storage polysaccharide glycogen in liver and skeletal muscle cells |
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Epinephrine effect |
Stimulates glycogen breakdown by activating a cytosolic enzyme ( glycogen phosphorylase) Does not activate directly Plasma membrane is involved in transmitting the epinephrine signal |
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Reception |
Detection after molecule binds to receptor protein |
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Transduction |
Receptor protein is changed which sets this step in process Can be a single step but is often a sequence of changes Relay molecules in pathway |
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Response |
Triggers activity in the cell ie: rearrangement of cytoskeleton or activation of a semicircular gene in nucleus |
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Cell signaling process ensures that crucial activities |
Occur in the right cells At the right time In proper coordination with other cells |
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Ligand |
A molecule that specifically bonds to another larger molecule Usually changes shape of receptor protein Aggregation of other receptor proteins |
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Most signal receptors are... |
Plasma membrane proteins and some are in the cell |
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Cell surface receptors make up... |
30% of human proteins |
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3 main types of membrane proteins |
1. G protein-coupled receptors 2. Receptor tyrosine kinases 3. Ion channel receptors |
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G protein-coupled receptor (GPCR) |
Cell surface membrane protein that works with help of a G protein Bind many signal molecules: yeast mating factors, epinephrine, hormones, and NTs |
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G proteins are... |
Largest family of cell-surface receptors Similar in structure Bind tonGTP |
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Receptor tyrosine kinases (RTK) |
plasma membrane receptors, a protein kinase (enzyme that catalyzes the transfer of phosphate groups from ATP to another protein)
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Process of GPCR (1) |
1. G protein receptor is attached and able to move along cytoplasmic side of membrane Functions like a on/off switch (pending GPD or GPT) When GDP is bound to G protein, it is inactive |
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Process of GPCR (2) |
Signal molecule binds to extra cellular side of receptor Receptor is activated and changes shape It’s cytoplasmic side binds an inactive G protein causing a GTP to replace the GPD and is then activated |
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Process ion gated (3) |
Ligand dissociates from receptor Channel closes |
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Important receptor in the nervous system... |
Ligand-gated ion channels NTs cross synapse and bind opening channels Ions flow in and trigger electrical signals down the axon Also include voltage-gated ion channels |
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Voltage-gated ion channels |
Respond to electrical signals instead of ligand Important in nervous system |
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Which receptor is associated with cancer? |
Abnormal functioning of RTK ie: in breast cancer-tumors may have excessive RTK receptors (called HER2) A protein developed called Herceptin binds to HER2 and inhibits cell division Increased survival rates by more than one third |
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Intercellular receptor proteins |
In cytoplasm or nucleus of certain cells Signal molecules (hydrophobic and very small) passes through cells plasma membranes Hormones (steroid and thyroid) and gases like nitric oxide Once enters cell, can turn off/on genes |
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How does it turn on/off genes |
Genes in cells DNA are transcribed and processed into mRNA mRNA leaves nucleus and is translated by ribosomes to produce specific proteins Special proteins called transcription factors control genes on/off switch |
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GPCR process (3) |
G protein dissociates from Receptor, diffuses along membrane and binds to enzyme, changing enzymes shape Once activated, the enzyme triggers a cellular response |
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GPCR process (4) |
Changes in G protein are temporary bc it also functions as a GTPase enzyme It hydrolyzes its bound GTP to GDP+Pi (this allows for the pathway to shut down rapidly when signaling molecule Ian no longer present) G-protein leaves enzyme inactive and returns to start for reuse. |
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RTK process (1) |
Exist as individual units called monomers Each has a extra cellular ligand binding site an alpha helix spanning the membrane and an intracellular tail containing multiple tyrosine
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Process RTKs(2) |
Signal molecule binds 2 monomers come together to form a dimer (called dimerization) |
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Process RTK (3) |
Dimerization activates the tyrosine kinase region of each monomer Each tyrosine kinase adds a phosphate from an ATP molecule to another T. On the other monomer |
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Process RTK (4) |
Receptor is now fully activated It is recognized by relay proteins in the cell Relay proteins bind to a phosphorylated tyrosine, changing the relay protein Triggers a transduction pathway leading to a cell response |
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Ligand gated ion channel |
Membrane channel with region acting as a gate when receptor changes shape |
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Process of ion channel receptors (1) |
Channel remains closed until a ligand binds to the receptor |
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Process ion channel (2) |
Ligand binds and channel opens Ions flow through and change concentration inside the cell This affects the activity of the cell |
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Process of GPCR (2) |
Signal molecule binds to extra cellular side of receptor Receptor is activated and changes shape It’s cytoplasmic side binds an inactive G protein causing a GTP to replace the GPD and is then activated |
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GPCR process (3) |
G protein dissociates from Receptor, diffuses along membrane and binds to enzyme, changing enzymes shape Once activated, the enzyme triggers a cellular response |
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GPCR process (4) |
Changes in G protein are temporary bc it also functions as a GTPase enzyme It hydrolyzes its bound GTP to GDP+Pi (this allows for the pathway to shut down rapidly when signaling molecule Ian no longer present) G-protein leaves enzyme inactive and returns to start for reuse. |
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RTK process (1) |
Exist as individual units called monomers Each has a extra cellular ligand binding site an alpha helix spanning the membrane and an intracellular tail containing multiple tyrosine
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Process RTKs(2) |
Signal molecule binds 2 monomers come together to form a dimer (called dimerization) |
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Process RTK (3) |
Dimerization activates the tyrosine kinase region of each monomer Each tyrosine kinase adds a phosphate from an ATP molecule to another T. On the other monomer |
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Process RTK (4) |
Receptor is now fully activated It is recognized by relay proteins in the cell Relay proteins bind to a phosphorylated tyrosine, changing the relay protein Triggers a transduction pathway leading to a cell response |
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GPCR process (3) |
G protein dissociates from Receptor, diffuses along membrane and binds to enzyme, changing enzymes shape Once activated, the enzyme triggers a cellular response |
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Process of ion channel receptors (1) |
Channel remains closed until a ligand binds to the receptor |
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Process ion channel (2) |
Ligand binds and channel opens Ions flow through and change concentration inside the cell This affects the activity of the cell |
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Process ion gated (3) |
Ligand dissociates from receptor Channel closes |
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Process RTK (3) |
Dimerization activates the tyrosine kinase region of each monomer Each tyrosine kinase adds a phosphate from an ATP molecule to another T. On the other monomer |
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Process RTK (4) |
Receptor is now fully activated It is recognized by relay proteins in the cell Relay proteins bind to a phosphorylated tyrosine, changing the relay protein Triggers a transduction pathway leading to a cell response |
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Ligand gated ion channel |
Membrane channel with region acting as a gate when receptor changes shape |
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Process of ion channel receptors (1) |
Channel remains closed until a ligand binds to the receptor |
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Process ion channel (2) |
Ligand binds and channel opens Ions flow through and change concentration inside the cell This affects the activity of the cell |
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Aldosterone |
Steroid hormone Secreted by adrenal glands, only receptors for this are in kidneys Acts as a transcription factor by turning on genes (in nucleus) Genes control flow of water and sodium thus affecting blood volume |
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Anenyly Cyclase |
An enzyme in the plasma membrane Converts ATP to cAMP in response to an extra cellular signal |
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Most widely used second messenger |
Cyclic AMP Usually activates serine/threonine kinase A |
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Further regulation of cell metabolism is provided by |
G-protein systems Inhibit adenyly cyclase Use different signal molecules to activate a different receptor that activates inhibitory G protein |
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How transduction pathway works |
Signal molecule binds to receptor and triggers chain of molecular actions Receptor activated another protein and then another (cascade) At each step the protein shape is changed to signal the next |
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What regulates protein activity? |
Phosphorylation (protein kinases transferring phosphates from ATP to protein) Many relay molecules are protein kinases creating a phosphorylation cascade |
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Another example of intercellular receptors.. |
Testosterone Acts as transcription factors to enter nucleus and turn on genes for male sex characteristics Only certain receptors respond |
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Transduction pathway |
Usually a multi step process Greatly amplify a signal Coordinate and regulate cellular response |
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Protein phosphatases |
Rapidly remove phosphates from proteins (dephosphorylation) Act as a molecular switch: turning on/off or up/down |
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Second messengers |
Small nonprotein water-solvable molecules or ions Spread through diffusion Participate in GPCRs and RTKs iE: cyclic AMP and CA ions |
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What regulates protein activity? |
Phosphorylation (protein kinases transferring phosphates from ATP to protein) Many relay molecules are protein kinases creating a phosphorylation cascade |
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Most protein kinases act on other substrate proteins unlike.. |
Tyrosine kinases They act on themselves |
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Most phosphorylation occurs at.. |
Serine or threonine amino acids of the substrate proteins |
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Protein phosphatases |
Rapidly remove phosphates from proteins (dephosphorylation) Act as a molecular switch: turning on/off or up/down |
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Second messengers |
Small nonprotein water-solvable molecules or ions Spread through diffusion Participate in GPCRs and RTKs iE: cyclic AMP and CA ions |
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The cells response to an extra cellular signal is |
Output response |
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Response to cell signaling |
Can be in either the nucleus or cytoplasm A signal transduction pathway leads to regulation of one or more cellular activities |
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Cytoplasmic response |
Pathways regulate the activity of enzymes rather than their synthesis ie: opening or closing an ion channel in plasma membrane or change in cell metabolism Signaling pathways can also affect the overall behavior of a cell ie: could lead to cell division |
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Nuclear response |
Regulate synthesis of enzymes or other proteins, usually by turning genes on/off in nucleus Final activated molecule in signaling pathway may function as a transcription factor Signal-growth factor, response-cell division |
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“Fine tuning” the response (regulation) |
A response to a signal may not be simply on or off 4 aspects of signal regulation to consider |
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Signal amplification (1of 4) |
At each step, number of activated products is much greater than in preceding step Enzyme cascades amplify cells response Proteins stay in active form long enough to process multiple molecules before inactive again iE: small number if epinephrine molecules on surface of muscle cell can lead to millions of glucose molecules |
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Specificity of cell signaling and coordinating the response |
Same signal can have different effects in cell with different proteins and pathways Different kinds of cells have different collections of proteins These different proteins (receptors, relay proteins, response proteins) allow cells to detect and respond to different signals |
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Signaling efficiency: scaffolding proteins and signaling complexes |
Scaffolding proteins are large relay proteins to which other relay proteins are attached Groups different proteins together that are in same pathway May activate relay proteins |
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Wiskott-Aldrich syndrome |
Absence of single relay protein can lead to abnormal bleeding, eczema, and predispositions to infections and leukemia The WAS protein is right beneath the immune cell surface and interacts with micro filaments of the cytoskeleton When not present, disrupts organization of cytoskeleton |
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Termination of signal |
Pathway needs to be a short time for next input If concentration of external signaling molecules falls, fewer receptors will be bound Unbound receptors revert to an inactive state If signaling pathway components become locked, whether active or inactive, proper function of cell can be disrupted |
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Different kinds of cells turn on... |
Different sets of genes |
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Apoptosis |
Cells infected or damaged or have reached the end of their functional lives undergo “programmed cell death” Prevents enzymes from leaking out of a dying cell and damaging other cells The cell shrinks, becomes lobed (blabbing) and packages in vesicles to be engulfed by scavenger cells |
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Triggered by signals that activate a cascade of “suicide proteins” in the cells programmed to die |
Apoptosis When the death cell signal is received, an apoptosis-inhibiting protein (Ced-9) is inactivated A cascade of caspase proteins(Ced-3) occurs the promote apoptosis |
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A master regulator of apoptosis |
Ced-9 Inactivated during Apoptosis Triggers caspase |
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How many pathways can carry out apoptosis in humans and mammals? |
About 15 Apoptosis can be triggered by signals from outside or inside the cell depending on the cell and the particular signal that initiates it |
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Internal signals of apoptosis can result from... |
Irreparable DNA damage or excessive protein misfolding |
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One major pathway for apoptosis |
Mitochondrial proteins that form pores on outer membrane cause it to leak and release other proteins that promote apoptosis or: cytochrome c |
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Cytochrome c |
In healthy cells-electron transporter in mitochondrial Cell death factor when leaked from mitochondrial |
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Process of apoptosis uses what proteins.. |
Ced-3, Ced-4, Ced-9 These are relay proteins capable of transiting the signal |
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Essential for development and maintenance of all animals |
Apoptosis Evolved early in evolution ie: normal part of development of hands/feet or paws |
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Diseases involving apoptosis |
Parkinson’s Alzheimer’s Cancer (can result from a failure of apoptosis leading to cancer) |
