Numerous metabolic pathways have been characterized using yeast, a single-celled eukaryote. Under aerobic conditions, yeast cells completely oxidize glucose to CO2 and H2O via glycolysis, the TCA cycle and the ETC. When oxygen is unavailable, yeast cells break down glucose into ethanol and CO2 (not lactate), via anaerobic glycolysis. Glucose (s) ? 2 Ethanol (l) + 2 CO2 (g) ?G°' = -235 kJ/mol In the 1860s, Louis Pasteur observed that when oxygen is added to an anaerobic suspension of yeast using glucose, the rate of glucose consumption is reduced drastically, along with the elimination of ethanol production. This is called the “Pasteur effect”. (a) Why does the accumulation of ethanol cease after the addition of oxygen? (b) What could be a possible reason for the decrease in the rate of glucose consumption observed in the presence of oxygen? (c) You are given a sample of 14C-labeled glucose, but you do not know which carbon atom is radiolabelled because the label on the package is damaged. You have been asked to identify which carbon is labeled. Having just completed BIOL201, you know exactly what to do. You add some of the 14C-labeled glucose to an anaerobic suspension of yeast cells and find that 14CO2 is produced along with non-labeled (non-radioactive) ethanol. i. Which of the six carbon atoms in glucose could have been 14C-labelled? Show your logic. ii. To find out exactly which carbon atom is radiolabelled, you prepare an extract of yeast cells capable of glycolysis, but with the isomerase enzyme catalyzing the Glyco-5 reaction specifically inhibited. Radiolabelled CO2 is still produced when radiolabelled glucose is supplied. Based on these results, which carbon atom of glucose do you predict was specifically radio-labelled? Show your logic.
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Fermentation, also known as Anaerobic Respiration Objectives: - Demonstrate carbon dioxide production during anaerobic respiration. - Understand the effects of inhibitors, intermediate compounds, and cofactors on anaerobic respiration. - Demonstrate practical applications of anaerobic respiration, such as making beer. Background: Living organisms respire, meaning that they have metabolic pathways that release energy from organic molecules and capture it in ATP. Some organisms need oxygen to do it, while others do not. However, they all respire because organisms need usable chemical energy for cellular processes. In most cells, respiration begins with the breakdown of glucose to pyruvate through a series of chemical reactions called glycolysis. Glycolysis can occur with or without oxygen. Organisms that live without oxygen are called anaerobes, and they reduce the pyruvate from glycolysis via anaerobic fermentation to either CO2 and ethanol (in plants and yeast) or lactic acid (in oxygen-stressed muscles of animals and some types of microbes). Part 1: Production of Carbon Dioxide during Anaerobic Fermentation In this procedure, you will observe the effects of various compounds on respiration. Pyruvate is the product of glycolysis, and it can be reduced to ethanol or lactic acid during anaerobic fermentation. Magnesium sulfate (MgSO4) provides Mg2+, a cofactor that activates some enzymes of glycolysis. Sodium fluoride (NaF) is an inhibitor of some enzymes of glycolysis. Glucose is a common organic molecule used as an energy source for respiration. Procedure: 1. Label the tubes and add the solutions listed in the following table. 2. Completely fill the remaining volume of the tubes with yeast suspension that is provided, and fill one tube completely with water. 3. For each tube, slide an inverted, large test-tube down over the yeast-filled tube. 4. Hold the yeast-filled tube firmly against the inside bottom of the cover tube and invert the assembly. 5. Measure the height of the liquid from the top of the inverted tube and record the measurement. 6. Incubate the tubes at 37 degrees for one hour. 7. After one hour, measure the height (in millimeters) of the bubble of accumulated CO2. 8. The effects of pyruvate, MgSO4, NaF, and glucose on CO2 production are best determined by pairwise comparisons of tubes for each variable.
Sri K.
BACKGROUND INFORMATION: Fermentation, just like cellular respiration, is preceded by glycolysis, a series of biochemical reactions that break a 6-carbon carbohydrate into two 3-carbon molecules of pyruvic acid. It is important to remember that glycolysis occurs in the cytoplasm in bacteria, not in some specialized organelle. In cellular respiration, after glycolysis takes place, the resulting molecules of pyruvic acid enter the Krebs cycle, followed by the mitochondrial electron transport chain. The pyruvic acid molecules are completely broken down to CO2, and more energy is produced. In fermentation, after glycolysis has generated two pyruvic acid molecules, these are turned into cellular energy (in the form of ATP), and some waste products, usually CO2 and ethanol, are formed. Fermentation can also occur in animal cells, specifically in muscle cells. In the absence of oxygen (a condition that can occur during exercise), muscle cells are able to produce energy by turning pyruvic acid into lactic acid. Since muscle cells cannot use the lactic acid, it is up to the bloodstream to gradually transport it to the liver, where it is metabolized. The two most widely known fermentations are ethanol and lactic acid fermentation. Ethanol fermentation is performed by yeast such as Saccharomyces cerevisiae and some bacteria such as Zymomonas. The waste products of this fermentation are ethanol and CO2. The general reaction for this type of fermentation is as follows: C6H12O6 → 2C2H5OH + 2CO2. Lactic acid fermentation is performed by some fungi and bacteria such as Lactobacillus. It can also occur in muscle cells. Lactic acid fermentation can be homolactic if two molecules of lactic acid are produced, and heterolactic if one molecule of lactic is produced along with other molecules. The general reaction for homolactic fermentation is as follows: C6H12O6 → 2C3H6O3. On the other hand, the reaction for heterolactic fermentation with CO2 and ethanol is: C6H12O6 → C3H6O3 + CO2 + C2H5OH. The products of heterolactic fermentation vary based on the enzymes bacterial species express. Therefore, analysis of the products of fermentation can be utilized to rule out possibilities of an unknown bacterium. What are the benefits of fermentation for some microorganisms? Why did our primate ancestors evolve the capacity to recognize fermented food?
Adi S.
Yeast converts glucose to ethanol and carbon dioxide during anaerobic fermentation as depicted in the simple chemical equation here: glucose $\longrightarrow$ ethanol $+$ carbon dioxide (a) If $200.0 \mathrm{g}$ of glucose is fully converted, what will be the total mass of ethanol and carbon dioxide produced? (b) If the fermentation is carried out in an open container, would you expect the mass of the container and contents after fermentation to be less than, greater than, or the same as the mass of the container and contents before fermentation? Explain. (c) If 97.7 g of carbon dioxide is produced, what mass of ethanol is produced?
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