Membrane Bound Transport Systems

Membrane Bound Transport Systems

	Membrane Bound Transport Systems -In this type of transport system all the proteins required for transport are firmly bound to the cell membranes. In E. coli about 40% of the transport systems belong to this class, which includes transport systems for sugars, ions and several amino acids. The membrane bound transport systems utilize Mitchell's proton motive force across the membrane to drive active transport
According to the hypothesis the hydrogen and electron transport carriers are arranged in loops in the membrane. Transfer of electrons down tbe chain is coupled to translocation of protons from one side of the membrane to the other (proton Translocation) This generates a proton concentration gradient or membrane potential across the membrane. The gradient tends to force the protons back from the outside to the inside, creating a proton motive force.
Thus solute movement is coupled to proton movement down the electrochemical gradient, bringing about accumulation of solutes. This system requires only one protein for lactose transport. The protein (M protein) is a tightly membrane bound product of the lac Y gene of the lactose operon
The protein constitutes about 40% of the membrane protein and has a molecular weigh of 30,000. The lactose carrier is a protein symport system. Movement of lactose across the membrane is coupled to proton movement (one proton per lactose molecule). The lactose carrier makes use of the membrane potential (negative on tbe inside) and pH gradient (alkaline on the inside). Exit of lactose from the cell moves the protons outside. This proton movement can be used to drive proline transport

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