Thread: help please urgent!

we just made a fermentation experiment with glucose molarities of 0.2, 0.4, 0.6, 0.8 and 1 M. We saw that the gas formed is the most in 0.2 M and is decreasing as the molarity increases. What is the reason that as molarity increases, amount of gas formed decreases? Shouldnt the amount of gas formed in a certain interval of time which was about 10 mins in our experiments increase up to a certain point and then become constant since this is an enzyme-substrate relationship? Please help! Urgent!

my guess is going to be that you messed up your dilutions (that is such a common error!)

The result was that you had your concentrations too high and it caused the cells to lyse.

well that could have been reasonable if i had prepared the glucose solutions but the solutions were prepared by the laboratory assistant. there is little chance that she got them mixed up.. could it be because glucose itself inhibits the fermentation reaction??? :?

maybe there is a negative feedback loop.

Maybe we really put them in a hypertonic solution. Does anyone have an idea what concentration of glucose would be hypertonic for yeast??

It's the feedback loop like I mentioned.

Normally you would think that increasing the concentration of glucose
should increase repiration. At low concentrations this is true. However,
the problem with glucose is that it capable of catabolic repression.
Glucose is the preferred carbon source for many strains of yeast, including
baker's yeast, Saccharomyces cerevisiae. At high concentrations, the
glucose causes catabolic repression. In high concentration it has the
ability to repress and regulate a number of metabolic pathways, including
those involved in respiration. Many of the enzymes that act in the
respiration cycles undergo feedback inhibition, by other intermediaries in
these pathways, but also can be regulated by high concentrations of
glucose. So in this case, at high concentrations, glucose actually causes
a reduction in respiration, because it is downregulating either the
production of enzymes involved in respiration or decreasing their activity.