MadSci Network: Biochemistry

Re: What order are fructose, glucose and sucrose fermented in terms of speed?

Date: Sat May 23 08:52:01 2009
Posted By: Karl A. Wilson, Faculty (Professor), Biological Sciences, S.U.N.Y. at Binghamton (Binghamton University)
Area of science: Biochemistry
ID: 1242661512.Bc

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
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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