Q.16 Which one of the following statements is correct about solute transport across
membranes?
(A) Passive transporters decrease the activation energy and does not facilitate the
transport of polar compounds
(B) The direction in which a charged solute tends to move spontaneously across a
membrane does not depend on the electrical gradient across the membrane
(C) All ABC transporters do not have nucleotide binding domain
(D) P–type ATPases get reversibly phosphorylated as a part of transport cycle
P-type ATPases undergo reversible phosphorylation during their transport cycle, making option (D) the correct answer for this CSIR NET Life Sciences question on solute transport across membranes.
Option Analysis
Passive transporters lower activation energy by providing a hydrophilic pathway, enabling polar compound transport, so (A) is incorrect.
Charged solutes move based on both concentration and electrical gradients, confirming (B) is false.
All ABC transporters feature nucleotide-binding domains for ATP hydrolysis, rendering (C) wrong.
P-type ATPases form a phosphoenzyme intermediate via aspartate phosphorylation, driving ion transport through conformational changes.
Solute transport across membranes is a core CSIR NET Life Sciences topic, covering passive diffusion, facilitated transport, and active pumps like P-type ATPases. This question tests understanding of transporter mechanisms essential for cell homeostasis.
Passive Transporters
Passive transporters, including channels and carriers, decrease activation energy by shielding polar solutes from the hydrophobic bilayer core. They facilitate polar compounds like glucose or ions down their electrochemical gradient without ATP. Option (A) wrongly claims no facilitation of polar compounds.
Charged Solute Movement
Charged solutes follow the electrochemical gradient, combining chemical (concentration) and electrical components. Positive ions move toward negative potential; option (B) ignores this dependency.
ABC Transporters
ABC transporters use two transmembrane domains and nucleotide-binding domains (NBDs) containing Walker motifs for ATP binding/hydrolysis. All possess NBDs, so (C) is incorrect.
P-Type ATPases Cycle
P-type ATPases, like Na+/K+-ATPase, autophosphorylate a conserved aspartate (E1 to E1P), causing conformational shifts for ion pumping (E2P dephosphorylation reverses this). This reversible phosphorylation powers primary active transport, validating (D).
