Cellular Respiration and Fermentation: Experimenting With CO2 and Redox Reactions
Julius Engel; Section 8
In this experiment, the subjects of study were fermentation, mitochondrial respiration, and redox reactions. In the first experiment, yeast was grown in various carbohydrate solutions at various temperatures. In the second experiment, succinate was added to various samples of a mitchondrial suspension, DPIP, and a buffer. Then after two blanks were used, the samples were placed into the spectrophotometer for transmittance testing. Introduction
Cellular respiration is a group of reactions that occur when a cell turns the energy from food and nutrient sources into ATP, releasing the rest of the products as waste. It is a catabolic set of reactions and they are defined as being exothermic redox reactions, meaning that energy is released and electrons are transferred. It takes place in the mitochondrial matrix within the cells.  Fermentation is an anaerobic, or lacking oxygen, reaction in which pyruvate is metabolized, NADH is oxidized to NAD+, and waste products are taken out so glycolysis can reoccur. Both of these processes are very significant for organisms because they are how organisms create their energy. Without these pathways, nutrients would not be converted to energy and the organism would be unable to do much of anything. Plants, animals, bacteria, fungi, and algae all use cellular repiration while fermentation is mostly used by plants and fungi, though lactic acid fermentation does occur in animals and in bacteria. In cellular respiration, glucose is the starting molecule which then undergoes glycolysis and is split into 2 pyruvate molecules. Oxygen is the final electron acceptor in the electron transport chain, meaning the ETC couldn’t occur without oxygen and cellular respiration could not be completed. Carbon dioxide is a product of cellular respiration and is released by the organism. In fermentation, glucose is again the initial molecule before glycolysis is performed, breaking the glucose down into pyruvic acid. But then, without any oxygen to use for cellular respiration, fermentation begins and pyruvate is converted to either lactic acid or alcohol. So oxygen doesn’t have a role in fermentation. Carbon dioxide however, is a product of fermentation, along with alcohol, when pyruvate becomes unstable and splits.
Carbohydrates are split into 3 main categories: monosaccharides, disaccharides, and polysaccharides. Monosaccharides are known as simple sugars, because of their simplicity in structure as opposed to its di- and poly- counterparts. Monosaccharides serve primarily as energy for organisms, as it can be broken down into carbon dioxide and water when in the presence of oxygen and energy is released. They also serve as “building blocks” for forming di- and polysaccharides.  Disaccharides are two monosaccharides that are bonded covalently. They serve primarily as a food source for monosaccharides and are in most food items that contain sugar. Polysaccharides are polymers of glucose (monosaccharide) and function primarily as an easy to access source of energy for an organism. The two major polysaccharides are starch and glycogen. Glycogen is stored in an organism when excess glucose is consumed. The glycogen is kept as an energy store so that at a later time when needed, it can be easily accessed and converted to glucose.
Redox reactions are reactions in which oxygen is gained (oxidation) and/or lost (reduction). Redox reactions play a critical role in the citric acid cycle because without the reduction of NAD+ to NADH, NADH couldn’t be sent to the electron transport chain, meaning the final stage of respiration couldn’t be completed and less energy would be created and made available to the organism. Also, FAD is used in the succinate/fumarate oxidation reaction as a prosthetic group in the enzyme, responsible for about 1.5 ATP molecules’ worth of energy....
References:  Carbohydrates [Internet]. Austin(Tx): [cited 2013 Nov 15] . Available from: http://www.austincc.edu/emeyerth/carbohyd.htm
 Stryer L, Berg J, Tymoczko JL (2002). Biochemistry. San Francisco: W.H. Freeman.
 Barnes SJ, Weitzman PD (June 1986). "Organization of citric acid cycle enzymes into a multienzyme cluster". FEBS Lett. 201 (2): 267–70.
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