Cellular respiration involves the process of producing the energy currency of living organisms

Cellular respiration involves the process of producing the energy currency of living organisms, ATP, through the oxidation of organic molecules such as carbohydrates and fats from food. (Reece, Taylor, Simon, & Dickey, 2011). Carbohydrates include sugars and polymers of sugars. Sugars are typically classified as monosaccharide, disaccharide, and polysaccharide. Monosaccharides also known as simple sugars, serve as the fundamental materials for the synthesis of amino acids, and other small organic molecules like fatty acids. Disaccharides are composed of two monosaccharides, joined by a glycosidic linkage. Polysaccharides are polymers or macromolecules which contain hundreds to thousands of monosaccharides bonded in glycosidic linkages. Lipids form the bilayers of cell membranes and also serve as reservoirs of energy, while protein, may also exist as an energy source. (Campbell, et al., 2009)
Anaerobic respiration, also known as fermentation takes place when all of the following conditions are satisfied: (1) glucose or other carbohydrates are oxidized incompletely in the absence of oxygen; (2) NADH is oxidized to NA+ for the continuation of the glycolytic pathway; (3) organic compounds were used as the terminal electron acceptors; and (4) a small amount of ATP is released. (Talaro & Chess, 2017).
Anaerobic Respiration (Duka, et al., 2018):
C_6 H_12 O_6?enzymes?2?CO?_2+2C_2 H_5 OH+energy (24,000 cal/mol)
C_6 H_12 O_6?enzymes?2C_3 H_6 O_3+energy (36,000 cal/mol)
Glucose acts as a fuel for cellular respiration. Glycolysis is the metabolic pathway that induces the production of ATP through the conversion of glucose into pyruvate. (Reece, Taylor, Simon, & Dickey, 2011). Glycolysis was derived from the Greek words, “glyk”, which means “sweet”, and “lysis”, which means “loosening”. It refers to the process that releases chemical energy from the breakdown of sugar. (Starr, Taggart, Evers, & Starr, 2015) In anaerobic respiration, the pyruvate can have two routes. Pyruvate can be reduced to lactate it can lose carbon dioxide to produce acetaldehyde, which is reduced to form ethanol. (Campbell & Farrell, 2012). Lactic acid fermentation occurs when pyruvate is reduced to lactate (C3H6O3), and NADH is oxidized to NAD+. Microbial fermentation is used in the dairy industry, and soy production. In alcohol fermentation, NADH is converted back to NAD+, and pyruvate is converted to carbon dioxide (CO2) and ethanol (C2H5OH). (Reece, Taylor, Simon, & Dickey, 2011). Enzymes work as biological catalysts that speed up the reaction by reacting on specific substrates, lowering energy barriers without being consumed in the reaction (Reece, Taylor, Simon, & Dickey, 2011). In reactions where enzymes are involved, the substrate binds to the active site of the enzyme to form a complex, then a transition-state species to produce the product. (Campbell & Farrell, 2012).
Yeasts are facultative anaerobes, which have the ability to produce ATP through oxidative phosphorylation or by fermentation, depending on the availability of oxygen in the environment. The bubbles produces by the CO2 is present in beer and champagne. It is also used in baking, to make the bread dough rise (Reece, Taylor, Simon, & Dickey, 2011). The Saccharomyces cerevisiae, also referred to as Baker’s yeast, is able to convert sugars into CO2 and ethanol aerobically and anaerobically. In the presence of oxygen (aerobic respiration), the Saccharomyces cerevisiae undergoes alcoholic fermentation until the consumption of sugar or glucose from the medium, while in the absence of oxygen (anaerobic respiration), acetaldehyde gets converted into ethanol under purely fermentative growth. (Hagman ; Piskur, 2015)