Hücre Zarında Transport Sistemleri ve Mekanizmaları
Hücre zarındaki taşıma sistemleri, enerji kullanımı ve mekanizmalarıyla ilgili detaylı açıklama ve örneklerle anlatım.
chat.question 1
chat.user
Attığım her şeyi ayrıntılı şekilde anlat. örneklerle
AI Asistan
chat.question 2
chat.user
Three general classes of transport systems When,asinthiscase,thetwosubstratesmoveinoppositedirections, theprocessisantiport. Insymport, twosubstrates aremovedsimultaneously inthesame direction. Aswenotedearlier,transportersthatcarryonlyonesubstrate,such astheerythrocyteglucosetransporter,areuniportsystems Note that this classification tells us nothing about whether these are energy requiring (active transport) or energy-independent (passive transport) processes Active Transport Results in Solute Movement against a Concentration or Electrochemical Gradient Inpassivetransport,thetransportedspeciesalwaysmovesdown its electrochemical gradient and is not accumulated above the equilibriumconcentration. Active transport, by contrast, results in the accumulationof a solute above the equilibrium point. Active transport is thermodynamically unfavorable (endergonic) and takes place only whencoupled(directlyorindirectly)toanexergonicprocesssuchas theabsorptionof sunlight,anoxidationreaction,thebreakdownof ATP,ortheconcomitant flowof someotherchemical speciesdown itselectrochemicalgradient. Active Transport Results in Solute Movement against a Concentration or Electrochemical Gradient In primary active transport, solute accumulation is coupled directly to an exergonic chemical reaction, such as conversion of ATP to ADP + Pi Secondary active transport occurs when endergonic (uphill) transport of one solute is coupled to the exergonic (downhill) flow of a different solute that was originally pumped uphill by primary active transport. 21.06.2019 10 Two types of active transport. (a) In primary active transport, the energy released by ATP hydrolysis drives solute movement against an electrochemical gradient. (b) In secondary active transport, a gradient of ion X (often Na+) has been established by primary active transport. Movement of X down its electrochemical gradient now provides the energy to drive cotransportof a second solute (S) against its electrochemical gradient. F-Type ATPasesAre Reversible, ATP-Driven Proton Pumps The F-typeATPase active transporters play a central role in energy-conserving reactions in mitochondria, bacteria, and chloroplasts. TheF-typeATPases catalyze theuphill transmembranepassageof protons driven by ATP hydrolysis (“F-type” originated in the identificationoftheseATPasesasenergy-couplingfactors). Structure of the FoF1 ATPase/ATP synthase. F-type ATPaseshave a peripheral domain, F1, consisting of three αsubunits, three βsubunits, one δsubunit (purple), and a central shaft (the γsubunit, green). The integral portion of F-type ATPases, Fo(yellow), has multiple copies of c, one a, and two b subunits. Foprovides a trans-membrane channel through which about four protons are pumped (red arrows) for each ATP hydrolyzed on the βsubunits of F1. 21.06.2019 11 F-Type ATPasesAre Reversible, ATP-Driven Proton Pumps ThereactioncatalyzedbyF-typeATPases is reversible,soaproton gradient cansupply theenergy todrive thereverse reaction,ATP synthesis.Whenfunctioninginthisdirection,theF-typeATPasesare more appropriately namedATP synthases. ATP synthases are central to ATP production in mitochondria during oxidative phosphorylationandinchloroplastsduringphotophosphorylation,as wellasineubacteriaandarchaebacteria.Theprotongradientneeded todriveATPsynthesis isproducedbyothertypesofprotonpumps poweredbysubstrateoxidationorsunlight.Asnotedabove Reversibility of F-type ATPases. An ATP-driven proton transporter also can catalyze ATP synthesis (red arrows) as protons flow down their electrochemical gradient. This is the central reaction in the processes of oxidative phosphorylation and photophosphorylation Lactose uptake in E. coli TheprimarytransportofH+outofthecell,drivenbytheoxidation of a variety of fuels, establishes both a proton gradient and an electricalpotential(insidenegative)acrossthemembrane. Secondaryactivetransportof lactoseintothecell involves symport ofH+andlactosebythelactosetransporter.Theuptakeof lactose againstitsconcentrationgradientisentirelydependentonthisinflow ofH+,drivenbytheelectrochemicalgradient
