Active transport is a process whereby the cell uses both transport proteins and metabolic energy to transport substances across the membrane against the concentration gradient. In this way, active transport allows cells to accumulate needed substances even when their concentration is lower outside the cell.
Group translocation is a form of active transport that can occur in prokaryotes. In this case of group translocation, a substance becomes chemically altered during its transport across a membrane so that once inside, the cytoplasmic membrane becomes impermeable to that substance and it remains within the cell. An example of group translocation in bacteria is the phosphotransferase system. A high-energy phosphate group from phosphoenolpyruvate is transferred by a series of enzymes to glucose. The final enzyme both phosphorylates the glucose and transports it across the membrane as glucose 6-phosphate.
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