Sugars catabolize through the process of glycolysis. Glycolysis causes the sugar to undergo phosphorylation and ferment, which yields CO2. In this experiment, different sugar solutions were mixed with a yeast solution. The yeast solution caused the sugar solutions to undergo glycolysis and produce CO2. Glucose, fructose, and mannose all produced CO2, yet galactose did not. Mannose and fructose followed very similar curves of time versus the production of CO2, while glucose followed a different curve. The ability for the sugar to undergo glycolysis was dependent on its ability to accept a phosphate group during phosphorylation. Therefore the sugar molecules most easily able to accept a phosphate group produced the most CO2.
Everyone knows that yeast makes dough rise, but exactly why does this happen? Sugars are broken down through the process of glycolysis (Black, 1999). In order to begin this catabolizing (breaking down) process, the sugar must first gain a phosphate group, which is called phosphorylation. Often the phosphate group is gained from ATP. Once the sugar has undergone these processes, it will begin to ferment and yield a byproduct of CO2. Buchner (1897) performed experiments using a yeast “juice” and different sugars such as can sugar, glucose, fructose, and maltose. When these two ingredients were combined, they reacted to produce CO2 for days. When the yeast juice alone was heated, it would also produce CO2. He also noticed that some sugars did not undergo the fermentation process with the yeast juice to produce CO2. In this study, different sugar solutions were combined with a yeast solution in order to see how fast and if they react to produce CO2.
A yeast solution along with three sugar solutions and laboratory instruments and supplies were distributed. The three sugar solutions included mannose, fructose, and glucose. A fourth sugar solution had to be concocted by measuring 1 g of raw galactose on a top loading scale and mixing it with 10 ml of distilled water measured in a graduated cylinder. The galactose and water were mixed in a test tube. All of the sugar solutions were 10% solutions.
Using a micropipettor, 2 ml of yeast solution and 2 ml of the first sugar solution, mannose, were measured and mixed together in a test tube. After being combined, a Pasteur pipette was filled with 1 ml of the new solution. “Play-Doh” was put on the tip of the pipette so that CO2 would not be able to escape and also to create vacuum so the solution would not fall out of the pipette. The pipette was then placed upside down in the test tube with the remaining solution of yeast and mannose. The pipette was then observed every 5 minutes to see if any CO2 had accumulated at the top. Any progress was recorded. This process was repeated with the rest of the sugar solutions. A control sample was also tested, using distilled water instead of a sugar solution. All of this was done at a room temperature of about 20º C.
|Sugar Type||Time (mins)||CO2 Produced (mL)|
Out of the samples that did produce CO2, the mannose sample took the longest to begin producing CO2 (Figure 1). It took 25 minutes until it started. Its biggest jumps in CO2 production were between the 20 minute and 25 minute, and 25 minute and 30 minute marks. This was when right when it began producing CO2. Its CO2 production increased steadily until the 65 minute mark when production started to even out.
The fructose sample took 20 minutes to begin producing CO2, which was second fastest out of the samples that did produce CO2. The fructose had its highest CO2 production in the first three time intervals it began producing CO2. After that it steadily increased and only seemed to slightly begin to even out production of CO2. It produced the most CO2 out of all the samples.
The glucose sample started producing CO2 the earliest out of all the samples, at the 15 minute mark. It increased production of CO2 steadily until the 45 minute mark when production suddenly spiked in production for 15 minutes. The CO2 production looked like it may have been starting to even out when recording stopped.
Galactose and the control sample did not produce any CO2 at all. They remained at 0 mL of CO2 production throughout the whole experiment.
Prescott and co-workers (1999) took a look at the chemical reactions between microorganisms and carbohydrates. They noted that the sugars glucose, fructose, and mannose are all catabolized, or broken down, through the process of phosphorylation, which is process of adding a phosphate group to a molecule (Black, 1999). Most commonly ATP adds the phosphate group to the sugar molecule, and then it is able to enter glycolysis, which is the process of breaking down a sugar. Once in the process of glycolysis, the sugar will begin to ferment. One common byproduct of fermentation is CO2.
In this experiment, glucose, fructose, and mannose were the only sugar solutions that produced CO2. As described by Prescott and co-workers (1999), those are the only sugars that are able to be broken down through phosphorylation. The yeast must have had ATP in it, which would have added a phosphate to the sugar molecules. After gaining the phosphate, the sugars began to break down, ferment, and produce CO2.
Prescott and co-workers (1999) also noted that in order for galactose to be catabolized, it must first go through a three-step process to be converted into a type of glucose. In the experiment, the galactose solution did not react with the yeast to produce any CO2. This is because the galactose was not converted, so therefore it could not gain a phosphate and begin the process of phosphorylation to break down, undergo glycolysis, ferment, and produce CO2.
Lastly, the control group did not produce any CO2 either. That is because there was nothing for it to react with and it was at room temperature. If the yeast was heated, it would have given off CO2 (Buchner, 1897).
Buchner, E. 1897. “Alcoholic Fermentation without Yeast Cells”.
Prescott et al., 1999. “Catabolism (breakdown) of Carbohydrates”.
Black, 1999. “Glycolysis and Fermentation”.