Chemical Reaction of Fermentation
Yeast don't ferment glucose into ethanol because it's fun; yeast does cause it needs to!
Questions: Why does yeast ferment glucose? Does fermentation of glucose to ethanol occur in an anaerobic or an aerobic type environment? If you were a winemaker, what conditions wold you account for while fermenting your grape juice? Any connections you can make past the given conditions of fermentation? (take quiz)
Questions: Why does yeast ferment glucose? Does fermentation of glucose to ethanol occur in an anaerobic or an aerobic type environment? If you were a winemaker, what conditions wold you account for while fermenting your grape juice? Any connections you can make past the given conditions of fermentation? (take quiz)
Yeast's Role in Fermentation
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Yeast contains enzymes to facilitate the fermentation of glucose to ethanol through anaerobic respiration. In living organisms there are two types of respiration, anaerobic and aerobic respiration. Anaerobic respiration occurs when there is no oxygen present to be used, contrary to aerobic respiration, in which oxygen is present. (13 ) As a result of anaerobic respiration and a lack of oxygen, lactic acid or in winemaking ethanol, is produced. Anaerobic respiration occurs often in single celled organisms such as yeast. Anaerobic respiration can sustain eukaryotic organisms like yeast as the 2 molecules of ATP are produced per respiration cycle, though larger cells would need larger amounts of ATP to be produced in aerobic respiration. (14)
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Conditions of Fermentation |
Fermentation of glucose in the wine making process is done within a layer of carbon dioxide to ensure that the reaction is anaerobic and not aerobic, as there is no presence of oxygen gas. (15) In aerobic respiration, water is produced instead of lactic acid or ethanol, which makes it essential for winemakers to facilitate the fermentation with the presence of carbon dioxide, instead of oxygen. (16)
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Why yeast ferment glucose?
Though yeast are just tiny single celled fungi, they too require energy. Yeast enzyme's break down glucose in order to create energy to "create" ATP to use as food. (17) The yeast by breaking down the glucose gains the energy from the breaking of these bonds and uses that energy to attach a third phosphate to ADP molecules. ADP stands for Adenosine Diphosphate, hence the fact it only has 2 phosphate molecules. Then a third phosphate molecule attaches to ADP to form ATP (Adenosine Triphosphate.) ATP's energy is stored in the bonds of the molecules, which are much stronger than the ADP bonds. (18) The ATP can release the third phosphate molecule when the yeast needs to use energy the energy stored in the bonds of ATP and ADP is formed again. Ethanol in this reaction is actually more of just a "byproduct" created from the yeast trying to get ATP for themselves.
In-depth Fermentation of Glucose
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1.) Glucose is first broken down by zymase enzymes in the yeast.
2.) When glucose is broken down, the energy released from breaking bonds, provides the necessary energy to add an additional phosphate molecule to ADP in order to form ATP, which yeast uses as energy.
3.) Pryuvic acid (C3H4O3) is formed after zymase enzymes break down glucose. (19)
4.) Carbon dioxide gas is released, which then forms Acetaldehyde (C2H4O.)
5.) Ethanol is finally produced after electrons carried from NADH molecules bond with Acetaldehyde. NADH turns back into NAD+ in order to continue the process of fermentation. (20) NADH and NAD+ act as electron carriers after the zymase enzymes break down the glucose and return them when ethanol is is.
2.) When glucose is broken down, the energy released from breaking bonds, provides the necessary energy to add an additional phosphate molecule to ADP in order to form ATP, which yeast uses as energy.
3.) Pryuvic acid (C3H4O3) is formed after zymase enzymes break down glucose. (19)
4.) Carbon dioxide gas is released, which then forms Acetaldehyde (C2H4O.)
5.) Ethanol is finally produced after electrons carried from NADH molecules bond with Acetaldehyde. NADH turns back into NAD+ in order to continue the process of fermentation. (20) NADH and NAD+ act as electron carriers after the zymase enzymes break down the glucose and return them when ethanol is is.