|MadSci Network: Biochemistry|
I am not surprised that the rate of CO2 production was higher with fructose and glucose compared to sucrose. Both glucose and fructose are simple sugars, monosaccharides. Both can be transported into the bakers yeast cell by facilitated diffusion by a high affinity carrier in the cell membrane. In contrast, sucrose is a disaccharide, and must first be hydrolyzed to its constituent glucose and fructose components by the enzyme invertase outside the yeast cell, then these monosaccharides are taken up. The real question is then why did you see a higher rate of CO2 production with fructose compared to glucose. Both fructose and glucose enter the glycolytic pathway through phosphorylation by the enzyme hexokinase. Both are eventually converted to fructose-6-phosphate. So it is not clear why fructose should be fermented faster. Two questions do occur to me that you should consider in interpreting your results: 1) Were the three sugars added in equal concentrations – specifically, at the same molar concentration (as opposed to weight)? 2) Was the same amount of yeast used in each reaction, and was the yeast equally “active”? 3) Finally, are you sure that your results are not just a fluke – something not obvious went wrong? In research we always run experiments with a number of replications and compare these results, to eliminate the possibility.
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