Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 4

Energetics of Carbohydrate Utilization. The anaerobic fermentation of free glucose has an ATP yield of two ATP molecules per molecule of glucose. For glucose units in a glycogen molecule, the yield is three ATP molecules per molecule of glucose. The corresponding value for the disaccharide sucrose is two ATP molecules per molecule of monosaccharide if the sucrose is eaten by an animal, but two and a half ATP molecules per molecule of monosaccharide if the sucrose is metabolized by a bacterium.
(a)Explain why the glucose units present in glycogen have a higher ATP yield than free glucose molecules.
(b)What is the likely mechanism for sucrose breakdown in the gut of an animal to explain the energy yield of two ATP molecules per molecule of monosaccharide
(c)Based on what you know about the process of glycogen breakdown, suggest a mechanism for bacterial sucrose metabolism that is consistent with an energy yield of two and a half ATP molecules per molecule of monosaccharide,
(d)What energy yield (in molecules of ATP per molecule of monosaccharide)would you predict for the bacterial catabolism of raffinose, a trisaccharide