Question

Alcohol is made in sealed containers (no O2). BRIEFLY discuss how Energy is created in EACH of the Three Cycles that would occur if the yeast containers were left open to air for the entire experiment. Do Not explain it using terms like “Aerobic/Anaerobic” or “Cellular Respiration/Fermentation”. Do not explain fermentation or discuss what yeast “Would Not Do”.

Answer 1

Answer:

Alcoholic Fermentation:-

• Alcoholic fermentation is the best known of the fermentation processes, and is involved in several important transformation, stabilization, and conservation processes for sugar-rich substrates, such as fruit, and fruit and vegetable juices.
• Alcoholic fermentation is carried out by yeasts and some other fungi and bacteria. The first step of the alcoholic fermentation pathway involves pyruvate, which is formed by yeast via the EMP pathway, while it is obtained through the ED pathway in the case of Zymomonas (bacteria).
• In the following step, the pyruvate is decarboxylated to acetaldehyde in a reaction that is catalyzed by the enzyme pyruvate decarboxylase.

• The redox balance of alcoholic fermentation is achieved by the regeneration of NAD+ during the reduction of acetaldehyde to ethanol, which is catalyzed by alcohol deydrogenase.
• The ATP yield of alcoholic fermentation is 1 or 2 mol of ATP per mole of glucose oxidized via the ED and EMP pathways, respectively. Zymomonas mobilis is the most important bacterial species that is able to perform alcoholic fermentation.
• The habitat of this species is the lymph of tropical trees, such as the palma tree from where it was originally isolated. Z. mobilis was proposed and used as a starter for ethanol production at the industrial level, although at present alcoholic fermentation carried out by yeast is better known and has been more thoroughly investigated.
• Natural alcoholic fermentation of fruit (cacao) and fruit juices (grape must and apple juice) is carried out by different microorganisms that act sequentially. The substrate fermentation is first achieved by apiculate yeast (Hanseniaspora), which is followed by elliptical yeast (Saccharomyces).
• Other fermenting yeast ascribed to the genera Candida, Kluyveromyces, Metschnikowia, Pichia, Saccharomycodes, Torulaspora, and Zygosaccharomyces are also sometimes found during natural alcoholic fermentation.
• It is well established that the most important agent of alcoholic fermentation is S. cerevisiae, the yeast that is used widely in several fermentation industries (wine, beer, cider, and bread) as a microbial starter. S. cerevisiae becomes the dominant species during alcoholic fermentation of fruit and fruit juices because of the strongly selective environment due to the low pH and high sugar and ethanol concentrations, and the anaerobic conditions.
• The ecological distribution of S. cerevisiae and the role of different habitats in the evolution of this species are controversial. Numerous investigations have revealed the low diffusion of this yeast species in natural environments such as soil, fruit surfaces, and tree exudates.
• On the other hand, S. cerevisiae is found widely in wineries and other fermentation plants since it is used to carry out the fermentation processes.
• In the winery, several environmental factors, including high ethanol and sugar concentrations, the presence of SO2, and others, can exert selective pressures on the S. cerevisiae population.
• Following these considerations, S. cerevisiae is defined as a domesticated species because of its selection through time in man-made environments.

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