ANAEROBIC AND AEROBIC METABOLISM
BCEM 341 – Winter 2014
Partner: Kendra Skalyn
Cells of all organisms can obtain energy through the combustion of sugars, either in the presence of oxygen (Aerobically) or without oxygen (Anaerobically). The purpose of this experiment was to perform a quantitative investigation of the differences between Anaerobic and Aerobic metabolism using pea seedlings and yeast organisms .
Aerobically, sugars such as glucose are transformed into pyruvate  and then into Acetyl CoA. This is then put through the citric acid cycle which is a series of reactions that oxidize acetyl units into carbon dioxide . Following the citric acid cycle, various enzymes are oxidized in the electron transport chain which creates a hydrogen ion gradient. This gradient then powers oxidative phosphorylation to generate large amounts of ATP  necessary for cellular survival. In this experiment, aerobic metabolism was studied by measuring the rate of oxygen consumption as a function of time in pea seedlings, chosen due to their rapid rates of respiration . Grown in the dark, these peas had underdeveloped chloroplasts and were unable to fully photosynthesize, making them perfect for this experiment . Aerobic metabolism proceeds with the overall net reaction of C6H12O6 + 6O2 6CO2 + 6H2O + approximately 32 ATP .
The experiment used a Volumeter to measure the change in oxygen consumed in a test tube which contained pea seedlings to one that contained only water (the control) . The experiment was performed twice using the seedlings, once in the presence of Ascarite and once without. Ascarite was used to absorb CO2 produced by the seedling, allowing only consumed O2 to be measured . The before and after mass of the pea seedlings were taken for the trial without Ascarite as this CO2 absorbing substance tends to dry out the seedlings far too much . The weight loss of the pea was used to predict the amount of oxygen consumed as it was assumed that all weight loss was due to glucose metabolism.
The second part of this experiment, the investigation of Anaerobic metabolism, was done by measuring the production of CO2 over time in yeast . Fermentation differs in that pyruvate is converted to ethanol in the absence of oxygen. Decarboxylation of pyruvate produced acetaldehyde which is then reduced to ethanol by NADH . Overall, the reaction of fermentation is C6H12O6 + 2ADP + 2Pi 2C2H5OH + 2CO2 + 2ATP . It can be noted that this is substantially less ATP than is produced during Aerobic metabolism. To ensure the yeast was producing CO2, Barium hydroxide (BaOH) was flooded with whatever gas was produced, hopefully to form an insoluble precipitate in the presence of CO2.
Measurements of CO2 produced were done using a Volumeter to compare production of a tube filled with yeast/glucose to a yeast/water and just water test tubes. The net rate of production of CO2 was calculated by subtracting the rate of CO2 production in yeast/water from that produced by yeast/glucose. The difference translated to the amount of CO2 produced from exogenous glucose molecules placed with the yeast. Methods
The procedure is as follows in the Lab Manual  on pages 5.1 to 5.5. The only change made to the procedure was during the aerobic experiment where the escape tubes were not clamped immediately. Instead, the apparatus and particularly the glass pipette and test tubes were allowed to adjust to the atmosphere pressures before clamping to ensure that there would be no large movements of the mineral oil position once the escape tubes has been closed off.
Upon inserting the stopper containing the side-arms into the Volumeter, immediate small shifts in the location of the mineral oil were observed. Tilting the side-arms allowed for the repositioning of the mineral oil. Upon applying the clamp to the...
References: 1) Fraser, M., Vogel, L. (2014). Lab Manual – Biochemistry of Life Processes. University of Calgary, pp 5.1-5.5
2) Tymoczko, J.L., Berg, J.M., Stryer, L. (2010). Biochemistry: A Short Course. 1st Ed. W.H. Freeman and Company, New York. Pp 226-233, 280-289.
3) Munich University. (2011). Yeast Metabolism. Retrieved March 19, 2014 from internet: http://biochemieweb.med.uni-monchen.de/yeast.biol/03%20Yeast%20metabolism.pdf.
4) Van’t Hoff, J.H., (1995) The Role of Osmotic Pressure in the Analogy Between Solution and Gases. Journal of membrane science, 100(1), pp. 39-44.
5) Siyna, A., (2011). Ascarite II Absorbents. Retrieved March 19, 2014 from internet: http://www.sigmaaldrich.com/chemistry/chemica-synthesis/learningcenter/technical-bulletins/al-1430/ascarite-ii-adsorbents-html.
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