28381991
Description
Flashcards by Katrina Oschmann, updated more than 1 year ago
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Created by Katrina Oschmann
almost 5 years ago
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| Question | Answer |
| signal transduction pathway (background info) | involves the binding of extracellular signaling molecules and ligands to receptors located on the cell surface or inside the cell that trigger events inside the cell, to invoke a response. ex - many pathways have been found in various organisms on Earth. details of signal transduction are very similar, giving support to evolutionary relatedness of life - believed that signaling mechanisms first evolved in ancient prokaryotes and single-celled eukaryotes...multi-cellular descendants then adopted them for their own use |
| quorum sensing | signaling molecules are given off by bacteria and allow them to monitor cell density; this is important when undergoing tasks that work best when there are many bacteria in the area ex - bacteria in squid's light organ |
| 3 ways cells can communicate | direct contact, local signaling long- distance signaling |
| direct contact* | cells that are in contact can pass signaling substances to one another - animal cells have gap junctions - plant cells have plasmodesmata (local signaling is not well understood in plants beyond the use of plasmodesmata due to the presence of a cell wall) - cells that are next to each other can communicate through cell-surface molecules |
| local signaling* | a) paracrine signaling - a secreting cell acts on nearby target cells by discharging molecules of a local regulator into extracellular fluid. ex - growth factor b) synaptic signaling - a nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell |
| long distance signaling | in endocrine, or hormone signaling, plants and animals release hormone molecules that are sent to other parts of the organism that will recognize and respond to the hormone - in animals, hormones travel through the circulatory system - in plants, hormones may move in vessels, through cells or diffuse as a gas hormones vary in size from the small ethylene, C2H4 molecule that causes fruit to ripen to the large insulin molecule that is made of thousands of atoms |
| 3 stages of cell signaling | reception, transduction, response |
| reception | 1) a signaling molecule binds with a receptor (protein) on the cell membrane, changing its shape - a signaling molecule will only interact with a receptor protein that is complimentary to... - the signaling molecule acts as a ligand, a molecule that specifically binds to another molecule, ligands are water-soluble and too large to pass through the cell membrane Reception in the Plasma membrane : 3 major types of cell-surface trans-membrane receptors |
| transduction | 2) the receptor changes so that it causes some process inside the cell; it is most often a multi-step pathway - relay molecules in a signal transduction pathway in a varied length of steps |
| response | the transduced signal causes the cellular response to occur (activation of cellular response like breaking down of glycogen) |
| G-protein coupled receptors | G-protein coupled receptors are used in yeast-mating factors, epinephrine, and other hormones and neurotransmitters - will play roles in embryonic development, sensory reception, and bacterial infections |
| G-protein coupled receptors steps | 1) the G protein acts like a switch - when GDP is bound to the G protein, it is inactive 2) when the signalling molecule binds to the extracellular side of the receptor, the receptor is activated, changes shape and binds to the G protein causing a GTP to displace and the GDP and it is activated 3) the activated G protein dissociates from the receptor, diffuses along the membrane and then binds to an enzyme, altering its shape and activity. the enzyme can now trigger the next step leading to a cellular response 4)the changes in the enzyme are temporary; the G protein acts a GTPase enzyme and hydrolyzes its bound GTP to GDP - this will continue to happen until the signaling molecule concentration goes down to a level that inactivates the pathway |
| receptor tyrosine kinases | a kinase is an enzyme that catalyzes the transfer of phosphate groups - one difference between a receptor tyrosine kinase and the G protein-coupled receptor is the fact that a tyrosine kinase can trigger many different transduction pathways and cellular responses - this allows the cell to regulate and coordinate many aspects of cell growth and cell reproduction |
| receptor tyrosine kinases steps | 1) before the signaling molecule binds, the receptors exist as individual units, or monomer. each is made of a helix spinning the membrane and an intracellular tail made of several tyrosines 2) when the signaling molecule binds, the 1 receptor monomers associate closely with each other and form a dimer (dimerization) 3) dimerization activates the tyrosine kinase region of each monomer; each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine on the tail of the other monomer 4) now that the receptor is fully activated, it is recognized by specific relay proteins inside the cell. each protein binds to a specific phosphorylated tyrosine, changes shape and triggers a transduction pathway leading to a cellular response |
| ion channel receptors (steps) | 1) a ligand-gated ion channel receptor will remain closed until a ligand binds to the receptor 2) the ligand binds to the receptor and the gates open, specific ions can flow through the channel and rapidly change the concentration of that particular ion 3) when the ligand dissociates from this receptor, the gate closes and ions no longer enter the cell - ligand-gated channels are important in nervous system (acetylcholine to signal muscle contractions) |
| intracellular receptors (steps/examples) | 1) the steroid hormone testosterone passes through the plasma membrane (is hydrophobic) 2) testosterone binds to a receptor protein in the cytoplasm 3) the hormone-receptor complex enters the nucleus, and binds to specific genes 4) the bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA 5) the mRNA is translated into a specific protein **remember that the genes in our DNA serve to make proteins as follows (DNA/transcription/nucleus to RNA/ribosome/translation into protein (with amino acid bases) so, the testosterone receptor acts as a transcription factor that turns on specific genes, here the genes' cod control male sex characteristics |
| transduction: cascades of molecular interactions relay signals from receptors to target molecules in the cell | the transduction stage of cell signaling is usual a multistep pathway some steps will include the addition or removal of phosphate groups or release of other small molecules or ions that act as messengers benefits: allows for amplification of the signal and allows for a high degree of coordination and regulation |
| signal transduction pathway (phosphorylation cascade) | 1) a relay molecule activates protein kinase 1 2) active PK1 transfers a phosphate from the ATP to an inactive molecule of PK2, activating it 3) active PK2 then catalyzes the phosphorylation (and activation) of Pk3 4) active PK3 phosphorylates a protein that brings about a cell's response to the signal 5) enzymes called protein phosphates (PP) catalyze the removal of the phosphates groups from the proteins, making them inactive and available for reuse |
| protein kinase | an enzyme that transfers phosphate groups from ATP to a protein. about 2% of our own genes are thought to code for protein kinases - examples of phosphorylation cascade: pathways triggered by mating factors pathways in animal cells by growth factors |
| protein phosphorylates | enzymes that remove phosphate groups from proteins (dephosphorylation) - by inactivating protein kinases, signal transduction pathways are turned off and the protein kinases are then available for reuse |
| Small Molecules and Ions as Second Messengers | some signal transduction pathways involve small, non-protein, water-soluble molecules or ions called second messengers (because the ligand is considered to be the first messenger) - since they are water soluble, they can spread through the cytoplasm easily - both G-protein coupled receptors and receptor tyrosine kinases can initiate pathways that use second messengers |
| cyclic AMP (cAMP) | an enzyme called adenylyl cyclase will convert ATP to cAMP when it is signaled by a ligand - the cAMP will then turn on the protein kinase A, then depending on the cell type, PKA will phosphorylate other proteins |
| Calcium ions (Ca2+) | calcium is more widely used than cAMP as a second messenger - Ca2+ works as a second messenger because its concentration in the cytosol is most often less than in the extracellular fluid increase of calcium in the cytosol causes reactions like -muscle cell contraction, secretion of certain substances, cell division, greening in response to light in plants |
| low calcium ion concentration in the cell maintained through - | -protein pumps in the cell membrane that pump Ca2+ out of the celling using ATP - protein pumps in the ER membrane that pump Ca2+ into the lumen of the ER (using ATP) -mitochondrial pumps, driven by chemiosmosis, that move Ca2+ into the mitochondrial matrix, when the concentration gets too high in the cytosol |
| inositol triphosphate (IP3) | calcium release can involve other second messengers like inositol triphosphate and diacylglycerol (DAG) - IP3 and DAG are made by the cleavage of a certain kind of phospholipid in the plasma membrane |
| response (cell signaling) | cell signaling leads to regulation of transcription or cytoplasmic activities - the response at the end of the signal transduction pathway may occur in the nucleus of the cell or in the cytoplasm |
| nuclear response | one way in which a signal transduction can control cellular activities is by turning specific genes on or off 1) signaling molecule (growth factor) triggers a phosphorylation cascade 2) the last phosphorylated kinase enters the nucleus 3) kinase activates gene-regulating protein called a transcription factor 4) the transcription factor stimulates transcription of a specific gene (or genes) 5) the mRNA then directs the synthesis of a particular protein in the cytoplasm the transcription factor may also regulate a gene by turning it off, often the transcription factor will regulate several different genes |
| cytoplasmic response | sometimes a signaling pathway may regulate the activity of proteins - the opening or closing of an ion channel, a change in cell metabolism, the response of liver cells to epinephrine to alter energy metabolism |
| 4 ways to fine tune a cellular response | there are four ways in which the cell will fine tune a response instead of turning it on and off 1) signal amplification 2) specificity of cell signaling and coordination of the response 3) signaling efficiency: scaffolding proteins and signaling complexes 4) termination of the signal |
| signal amplification | each step of a cascade, the number of activated products is much greater than in the preceding step (see epinephrine pathway above) - each protein persists in an active form long enough to process many molecules of substrate before they become inactive again - so, a small number of signaling molecules, like epinephrine can lead to the release of hundreds of millions of molecules like the glucose from glycogen |
| specificity of cell signaling and coordination of the response | the response of a particular cell to a signal depends on a particular collection of signal receptor proteins, relay proteins and proteins needed to carry out the response |
| signaling efficiency: scaffolding proteins and signaling complexes | the diagrams that we have used are simplified; they only show a few relay molecules, however, most relay molecules are proteins and proteins are very large and therefore cannot move quickly through the cytoplasm how does a protein kinase find its substrate? - scaffolding proteins are large relay proteins to which several other relay proteins are attached to at the same time - this means that one scaffolding protein can simultaneously produce several different cellular responses - the speed an accuracy of the signal between cells is enhanced because the cell doesn't have to wait for the diffusion of the proteins in the cell |
| termination of the signal | for a cell of a multicellular organism to remain capable of responding to incoming signals, each molecular change in its signaling pathways must last only a short time - for this to happen, the changes produced by prior signals must be reversible - the cellular response happens only when the concentration of signaling molecules is at a certain threshold the number of active receptors falls below the threshold > the relay molecules return to their active forms > the cell is ready to respond to a fresh signal |
| dna transcription |
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