Question

Yeast cells need to convert all sugars to glucose before they can perform glycolysis. Some carbohydrates need to be prepared in longer metabolic pathways than others. Write a prediction about the efficiency of respiration for each of the three food sources given the properties listed below. (Note: an equal mass of sugar was used in each case)

Glucose, Sucrose, Maltose

1. Glucose is ready for glycolysis.
2. Maltose is a disaccharide made from two glucose monomers. The glycosidic bond between the monosaccharides must be hydrolyzed before glycolysis can begin.
3. Sucrose is a disaccharide made from one glucose and one fructose. First, the glycosidic bond between the monosaccharides must be hydrolyzed, then the fructose must be converted to glucose by another enzyme.

Answer 1

Glucose is a monosaccharide and is ready for glycolysis by the yeast. So the efficiency of respiration would be the highest.

Maltose is a disaccharide made from two glucose monomers. Since the glycosidic bond between the monosaccharides must be hydrolyzed to give the two glucose monomers glycolysis cannot immediately begin. The efficiency of respiration would be relatively lower when compared to glucose.

Sucrose is a disaccharide made from one glucose and one fructose. The glycosidic bond between the monosaccharides are to be hydrolyzed and then the fructose must be converted to glucose by another enzyme. Therefore the efficiency of respiration would be relatively lower with sucrose as well.