Why is energy required for nutrient transport? Give an example of a system that transports nutrients and describe what source of energy is used to move the nutrients into the cell
What will be an ideal response?
Answer: Energy is required for nutrient transport because nutrient concentration outside of the cell is lower than the nutrient concentrations inside the cell, thus nutrient transport moves solutes against a concentration gradient and requires energy. There are three examples in the text. The student could describe any one of them. They are (i) Simple transporter such as lac permease. Each nutrient molecule is cotransported into the cell with a H+ ion, thus the proton motive force provides the energy to transport nutrients. (ii) Group translocation such as sugar phosphotransferases. Each nutrient molecule is modified during the transport process. The modification, in this case, phosphorylation, releases energy, thus the energy source is an energy-rich compound such as phosphoenol pyruvate or some other phosphorylated compound. (iii) ABC transporters. In this example specific binding proteins bind to nutrient molecules with high affinity. Movement of the nutrient into the cell is coupled to ATP hydrolysis, thus ATP is the source of energy for transporting nutrients.
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