Which of the following substances must be further digested before it can be absorbed by specific carriers in intestinal cells? A. Sucrose B. Dipeptides C. Alanine D. Fructose
A
The substance that must be further digested before it can be absorbed by specific carriers in intestinal cells is option D, fructose.
Fructose is a monosaccharide and it can be transported across the intestinal epithelium by facilitated diffusion, but it requires the help of specific transporters such as GLUT5. However, these transporters have a limited capacity, which means that excess fructose that cannot be transported will remain in the intestine and be fermented by bacteria, leading to gastrointestinal symptoms.
Therefore, before it can be absorbed efficiently by the intestinal cells, fructose must first be broken down into glucose and another simple sugar called fructose-1-phosphate by the enzyme fructokinase. This process occurs mainly in the liver and kidneys and requires ATP. Once converted to glucose, fructose can then enter the bloodstream and be used by the cells of the body for energy.
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