Flashcards
PhysMet - Lecture 14
Cards in this deck (32)
- 1Cells never exist in isolation, even single celled organisms interact with.?A: …their environment and receive/act on signals from beyond their plasma membrane (and once they reproduce/replicate themselves they start to interact with each other.
- 2Aspects of cell behaviour controlled by signalling?Growth, Differentiation, Development, Metabolism
- 3What will happen if a cell a) doesn’t receive any signals or b) receives too many/inappropriate signals..?a) it will die b) it may divide at the wrong rate (e.g. cancer [too rapid], diabetes, heart/ neurological diseases)
- 4Examples of types of signals released/received?pH changes, osmotic changes, food ingestion, oxygen presence, light, noxious chemicals (predators/prey may release pheromones that alert other organisms to their presence/location)
- 5What is the basic universal signal pathway?Signal >> Receptor >> Response. E,g, S: presence/lack of nutrients in local environment. R: bacteria recognise this presence/lack of nutrients through plasma membrane receptors. R: bacteria use flagella to drive them towards food source/form endospores and biofilms under nutrient starvation.
- 6What signals do plants/animals/unicellular eukaryotes respond to?plants – variations in sunlight, growth hormones, gravity; animals – metabolic activities of neighbouring cells, developmental signals during embryogenesis (homeobox localisation), ion/glucose concentrations; unicellular – local environment, mating signals etc.
- 7—- Beyond the plasma
- Small signals….give a larger response (NB: this can be done rapidly)
- Chemical…..gene expression (NB: either metabolism or physiology of cell is altered)
- 8What is the problem with amplified systems? How is the problem dealt with?They can lead to positive feedback mechanisms running constantly on a loop. To counteract this regulatory mechanisms monitor closely changes in metabolism/physiology (genetic alterations) and send their own signals to ensure the amplified signal is large but short (dampen the system) or the receptor is turned off.
- 9Signals are received from an..1..or..2.. and received by a..3.. cell. Most signals are..4..; they bind. If a signal stimulates a pathway it is an..5.. If it inhibits a pathway it is an..6.. Most drugs are..7..and most natural ..8.. signals are ....9....1) an environmental stimulus; 2) signalling cell; 3) target cell; 4) ligands; 5) agonist; 6) antagonist; 7) antagonists; 8) ligand; 9) agonists
- 10Describe signalling by direct contact and when it might occur?When a protein (ligand) bound to the signalling cell (e.g. transmembrane protein) binds to a receptor on the target cell. Usually occurs in tissue development (e. cell-to-cell contact controls eye development in drosophila)
- 11Describe signalling by gap junctions and when might it be used?exchange small (<1.2 kDA) signalling protein molecules/ions to coordinate metabolic reactions b/w cells e.g. for use w/electrical synapses or during embryo development (both require rapid communication b/w neighbouring cells).
- 12What are connexins?Structurally related transmembrane proteins that assemble to form hexameric connexons which, when paired, make up gap junctions (in vertebrate organisms).
- 13Describe autocrine signalling and mention when it might be used?signalling whereby a cell produces a ligand and responds to it itself. Happens because the autocrine signal has a very short half-life (rapid degradation in extracellular medium) so can’t diffuse far enough to reach neighbouring cells. Autocrine signalling used to enforce developmental decisions (e.g. cell may use autocrine ligands to amplify the action of switches used to drive a genetic pathway)
- 14which type of signalling is common to cancers?autocrine signalling because it allows for auto-production of growth hormones that stimulate cell proliferation (tumours)
- 15What are eicosanoid ligands?Acts as an antagonist; interferes with the integration of pain and inflammation
- 16What is paracrine signalling?when a ligand molecule released from one cell causes a response in local (neighbouring) cells. The signal doesn’t last long because the molecules have a rapid half life (almost as short as autocrine)
- 17Example of a paracrine response?Neuromuscular junction; Ach released by presynaptic neuron stimulates opening of channels on postsynaptic membrane causing influx of Na+ ions into muscle tissue. AchE acts to quickly breakdown Ach in the synaptic junction so that the muscle is not continuously stimulated. Postsynaptic channels close.
- 18What is endocrine signalling? Name of signal released? Location of target cells? Tissue examples? Difference between endocrine and exocrine?It’s systemic; produced in one type of cell (endocrine) and acts on another. Signals released are called hormones. These travel in the blood until they reach distant target cells. Examples include pituitary, thyroid, and adrenal glands. Endocrine hormones are released into blood vessels, exocrine tissues release their products through ducts onto another surface within he body or outside the body.
- 19—A) gap junction B) paracrine C) autocrine D) endocrine E) direct contact
- 20Specificity is provided by what two mechanisms?Cell-type specific expression and receptor affinity to ligands.
- 21What is cell-type specific expression?when ligands are only able to activate/induce a response from cells that either a) carry a receptor with complementary shape or b) cells that contain the necessary molecules to enable a ligand induced cascade reaction further downstream.
- 22What is the mechanism for cell-type specificity?Enhancer control elements that combine mediator proteins to interact with the phosphorylated C-terminal tail of RNA polymerase and turn a gene on and silencer control elements that turn a gene off (as in the lac operon of bact). These determine what receptors are present on the plasma membrane.
- 23What is ligand affinity?The non-covalent mediation of precise molecular complementarity between ligand and receptor.
- 24What is Kd and why do we use it as a measure of ligand affinity?Kd = [R][L]/[RL] (where ‘RL’ = the receptor-ligand complex). Kd is the equilibrium dissociation constant and is used because it yields the familiar unit M, or molar/moles per litre, so affinity can b described in terms of concentration.
- 25Is affinity greater at lower or higher values for dissociation?Affinity is greatest when dissociation values are smallest. For example, an affinity of 10-14 M means that even at very, very low concentrations of a ligand, half of the ligand is still bound to the receptor (equilibrium) (i.e. it is not necessary to saturate receptor surroundings w/ligand to encourage a successful RL-complex to form, their attraction is so strong that it is almost instantaneous anyway). 10-6 M would be a much lower affinity.
- 26What does low affinity mean for specificity of a signal? What is a common trait of low affinity chemical substances?low affinity means low specificity. Often substances like this will interact with non-specifically with most things (e.g. as blocking agents – BSA). Low affinity substances are also usually quite sticky.
- 27For small signalling molecules, their affinity is in what region of Kd? 1010 M, 10-10 M, 10-100 M. What is the difference in concentration between NaCl and the signal molecules?10-10 (aka nanomolar range). That means that if the ligand is available at 10-10 M then half of it will bind to receptors. Signal molecules will occupy receptors at concentrations 140 million times lower than that of [NaCl] in the blood.
- 28By what mechanism are signals usually amplified? Explain briefly how this mechanism works.by use of an enzyme cascade. Signal binds to a receptor and stimulates conversion of target molecules, which then themselves stimulate/catalyse further conversion of a second enzyme, etc…all together signal is amplified in picoseconds.
- 29What is signal desensitisation and what does it mean for the signal transduction pathway? How is this reset? Example in action?when a signal is presented continuously the transduction pathway becomes desensitised to it (i.e. a receptor is inactivated/removed by dephosphorylation for example). When high stimulation is reduced though (i.e. stimulation falls below a threshold level) the system is reset.
For example, noxious smells are pungent when you first walk into a room but quickly become undetectable, however, if you walk out of the room for a time and re-enter the smell is suddenly noticeable once again. - 30How many signal transduction pathways does desensitisation control/impact?Desensitisation can only control one signal received by one receptor. If multiple signals are incoming into a cell (as in cross-talking) the desensitisation process will only act upon one signal receptor to bring it below a threshold level. So, each signal transduction pathway has its own individually turned on desensitisation mechanism, even though two or more of these may work in the same way.
- 31What is the cross-talk process/signal integration? Analogy for both?When two separate signal pathways communicate with each other by acting on the same enzyme cascade. Could be 2+ agonistic/antagonistic signals, or a combination of multiple agonistic/antagonistic ligand induced responses.
Cross-talking works like a dimmer switch that can be finetuned, increased or decreased, to match signal intensity. Integration is how these separate responses are combined to induce a shared response (the intensity of the light emitted). - 32—1) Affinity
2) Differential
3) Amplification
4) Desensitisation
5) Cross-talk
6) Integrated
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- Flashcards on PhysMet - Lecture 14, created by Tolu Lip on 15/04/2019.
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