Q.76 Which of the following is/are active transport mechanism(s) in prokaryotes where
the substance is chemically altered during transport across the membrane?
(A) Group translocation
(B) Simple diffusion
(C) Facilitated diffusion
(D) Osmosis

Answer: (A) Group translocation

Group translocation represents the sole active transport mechanism in prokaryotes that chemically modifies the transported substance during membrane crossing. This process ensures efficient nutrient uptake by altering molecules like sugars via phosphorylation. Other options involve passive transport without energy input or chemical changes.​

Option Analysis

(A) Group Translocation

Group translocation qualifies as active transport unique to prokaryotes, where substances undergo chemical alteration—typically phosphorylation—during translocation across the cytoplasmic membrane. The phosphoenolpyruvate:sugar phosphotransferase system (PTS) exemplifies this, converting glucose to glucose-6-phosphate in bacteria like E. coli, preventing efflux and enabling continuous uptake against gradients using metabolic energy.​

(B) Simple Diffusion

Simple diffusion constitutes passive transport, allowing small nonpolar molecules like O₂ or CO₂ to cross membranes down concentration gradients without proteins, energy, or chemical modification. Prokaryotes rely on it for gases, but it fails against gradients or for polar solutes.​

(C) Facilitated Diffusion

Facilitated diffusion remains passive, using channel or carrier proteins to move polar or charged molecules down gradients without energy or alteration. In prokaryotes, it handles ions or sugars like lactose, but cannot achieve active accumulation.​

(D) Osmosis

Osmosis denotes passive water movement across semipermeable membranes down its gradient, driven by solute concentration differences, with no chemical change to water. Prokaryotic cells with walls manage osmotic stress, but this lacks active energy use.​

Introduction to Active Transport Mechanism in Prokaryotes

Prokaryotes employ diverse strategies for nutrient uptake, with group translocation standing out as the active transport mechanism in prokaryotes involving chemical alteration of substrates during translocation. This process powers essential bacterial metabolism, particularly for sugars, distinguishing it from passive methods prevalent in competitive exams like CSIR NET Life Sciences.​

What Makes Group Translocation Unique?

Group translocation drives active transport by phosphorylating incoming molecules via the PTS, using phosphoenolpyruvate (PEP) as the energy source. In E. coli and Bacillus subtilis, glucose enters as glucose-6-phosphate, trapping it intracellularly and creating a favorable gradient despite high external concentrations. This chemical modification ensures one-way uptake, vital for prokaryotic survival in nutrient-scarce environments.​

Comparing Transport Mechanisms

Passive transports dominate options (B)-(D), lacking energy or modification:

This table highlights why only group translocation fits the query criteria.​

Relevance for CSIR NET Preparation

Mastering the active transport mechanism in prokaryotes proves crucial for CSIR NET questions on bacterial physiology and membrane transport. Recognize group translocation’s hallmark chemical alteration to differentiate it swiftly in MCQs.​