Which of the following is not a characteristic of secondary active transport?
Secondary active transport refers to movement of solute against its concentration gradient energized indirectly by ion electrochemical gradient established by primary active pumps, not by direct ATP binding and hydrolysis at transport protein itself. Hallmarks include dependence on Na+/K+ ATPase or H+-ATPase to maintain Na+ or H+ motive force, inhibition by collapse of gradient with ionophores or ouabain, and involvement of symport or antiport mechanisms where downhill flow of driving ion drags substrate uphill. Protein operates by alternating access rocker-switch mechanism without Walker A ATP-binding motifs. Therefore direct ATP consumption at transporter characterizes primary active class exemplified by P-type ATPases such as Na+/K+ ATPase, Ca2+ ATPase SERCA, and ABC exporters where ATP hydrolysis at NBDs directly powers movement. Assigning direct ATP utilization to secondary systems is inaccurate; they utilize gradient, so feature of primary pumps cannot be defining for secondary transport. Symport and antiport, gradient utilization remain defining features. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.
Ref: Alberts et al., 7th ed., Chapter 11, Distinction primary vs secondary active transport.