QUESTION : How did the bacteria maintain its homeostasis when homeostatic disturbance occur. Explain your answer the way you understand the process of sensing and signalling see pictures below Sensing and SignalingMicrobial signalingSignal receives by the cell are mostly chemical signals from the extracellular fluid environment:either it comes from the external environment or mostly from other cells. There are 3 sequential stepsinvolve when cells response to any signals. Initially, the signal binds to a receptor protein in the cell whichare mostly found at the outside surface of the cell membrane. Then, the binding of the signal will cause theconveying of a message into the inside of the cell where the message will be amplified. The cell then willchange its activity as a respond to the signal.The entire signaling process, from signal detection to final response is called the signaltransduction pathway. The pathway involves a signal, a receptor, transduction and effects.In this topic, E. coli will be used as a sample organism. E. coli thrives in the human intestine. Thesolute concentration that surrounds the bacterium is every so often increases than that of the inside of thebacterial cell. When this happens, water will diffuse out of the cell and the solute will diffuse into the cell.The bacterial cell then will lose its homeostasis and may result to cell death. To prevent this, the microbialcell has installed mechanisms allowing it to perceived signals for incoming event and induced a specificresponse to maintain homeostasis. The microbial process involved in microbial signaling is very similar tothe signal transduction pathway used by more complex organisms. The signal transduction pathway hastwo major components: a receptor and a responder.SignalingProkaryotes just like eukaryotes can sense information from their environment. The informationcan be in the form of a physical stimulus such as when the rain touch your skin or a chemical stimuluswhen a bacteria sense the presence of protein or sugar in an exposed food. The information or signals maynot come only from the environment but it may also be produced by the organism itself such as thechemical signals sent out by the ants when they sense the presence of food.However, not all signals received by the organisms or of the microbial cells are being responded to.It is just like when we do not respond to all the sounds that we heard from our environment. Why is this so?It is because, to be able to respond, the cell must have a specific receptor protein that can bind to aspecific signal for the cell to process it. However, cells has only receptors for some signals. Whichreceptor a cell may have depends whether the cell has transcribed the genes for that particular receptorand whether that gene has been translated.The receptorA receptor protein is the first component of a signal transduction pathway. Receptors are usuallyfound extending from the cell membrane to the outer membrane. Receptor protein is signal specific.Failure of organism to respond to a certain signal may be due to the absence of a specific receptor protein.In this example, the specific receptor protein for changes in the solute concentration in E. coli is calledEnvZ. Envz is a transmembrane protein that extends from the bacterium's plasma membrane into thespace between the plasma membrane and the highly porous outer membrane which formed a complex withthe bacterial cell wall. When the solute concentration in the extracellular environment increases, the soluteconcentration in the spaces between the two membranes also increases.The change in the soluteconcentration served as a signal for the receptor protein to undergo a structural change (change in shape).The structural change in EnvZ converts the receptor protein into an enzyme protein kinase. Protein kinasecatalyzes the addition of a phosphate group from ATP to one of the EnvZ's histidine residue, a processknown to be self-phosphorylation. The conformational change in the intermembrane domain (where thereceptor protein lies) is transmitted to the domain in the cytoplasm which initiates signal transduction. .The responderThe responder is the second component of the signal transduction pathway.The chargephosphate group added to the histidine residue earlier by Protein kinase causes the cytoplasmic domain ofEnvz protein to change its shape again. These time, the changed EnvZ protein is now bounded to asecond protein OmpR, which removed the phosphate group from EnvZ. The phosphorylation results tochanging the shape of OmpR. This change in a responder is a key event in signaling for the followingreasons:* The signal from the outside of the cell has now been transduced to a protein within the cell'scytoplasm.* The phosphorylated OmpR can bind to a promoter on E.coli DNA adjacent to the sequence thatcodes for the protein OmpC. The binding process initiate the final phase of the signaling pathway: the effect of the signal which is the alteration in the cell function* The signal has been amplified. A single enzyme (kinase) can catalyze the conversion of manysubstrate molecule, one EnvZ molecule alters the structure of many OmpR molecules.The phosphorylated OmpR is a transcription factor with the correct three-dimensional structureneeded to bind the promoter of the OmpC gene, resulting in the increase in the transcription of that gene.Translation of OmpC MRNA results in the production of OmpC protein, which leads to the response thatregulates the osmotic pressure. The OmpC protein is inserted into the outer membrane of the bacterialcell wall , where it blocks the pores and prevent solutes from entering the intermembrane space. As aresult, the solute concentration in the intermembrane space lowers, and osmotic balance is restored. The E.coli then keep on behaving as if nothing happens.SoluteIntermembraneEnvironmentSignalSolutes enter the space betweenthe two membranes throughlarge pores in the outermembrane of E. coli.(signal)spaceOutermembraneof bacteriumPlasmamembraneeceptorThe EnvZ membrane protein changesshape in response to the high soluteconcentration, catalyzing theaddition of a phosphate from ATP.EnvZCellwallLATPADP)CytoplasmTransductionThe phosphate from EnvZ istransferred to the OmpR protein......and the phosphorylatedOmpR changes shape, enablingit to bind to DNA and stimulatetranscription of the ompC gene.OmpRDNAompCEffectsOmpC protein inserts into the outermembrane, preventing solute entryand keeping the cell's exteriorosmotically balanced.MRNAProteinsynthesisOmpCproteinPoresA model transduction signal pathway in E. coliMajor features in the prokaryotic system signalingA receptor changes its conformation upon binding with a signalA conformational change in the receptor results in protein kinase activity* Phosphorylation alters the function of a responder protein* The signal is amplified* A transcription factor is activated* The synthesis of a specific protein is turned on* The action of the protein alters cell activityThe ligand-receptor complexReceptor proteins binds to a signal molecule very specifically just like when an enzyme binds to asubstrate. The specificity of binding determines which specific cell responds to which signals. Receptorshave specific binding sites for their signals. A specific signal molecule will fit and bind into a site on itsreceptor protein called a ligand. The binding of the ligand causes the receptor protein to change its 3dimensional structure. The change in shape of the receptor protein initiates a cellular response. Theligand has nothing to do with the cellular response but is simply responsible for initiating the reaction. Theligand-receptor complex is a reversible process. Meaning, after initiating the reaction, the ligand shouldbe released or else, the receptor will be continuously stimulated. In cases where inhibitors also bind in theligand binding site of the proteins, then binding of the ligand to the receptor binding site will not bepossible. Hence, no possible signaling will occur.

The bacteria the example of prokaryotic organisms that do not contain any membrane bound cell…

Answered: QUESTION : How did the bacteria…

Human Anatomy & Physiology (11th Edition)

11th Edition

ISBN:9780134580999

Author:Elaine N. Marieb, Katja N. Hoehn

Publisher:Elaine N. Marieb, Katja N. Hoehn

Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...

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