Cellular Respiration of Living Organisms - Research Paper Example

Biology Research Paper 11 April Cellular Respiration Introduction All living organisms require energy to drive all the chemical reactions that are required to sustain life. The phrase cellular respiration denotes the biochemical channel through which cells free energy from the chemical bonds of food molecules. It also encompasses the processes that make this energy available to energy-requiring reactions. Respiration occurs in two major forms namely aerobic and anaerobic. Aerobic (cellular) respiration occurs when oxygen is available, whereas anaerobic respiration, which is also referred to as fermentation, takes place when oxygen is unavailable. In prokaryotic cells, cellular respiration occurs in the cytoplasm of the cells in addition to other inner cell surfaces. Conversely, eukaryotic cells possess specialized organelles referred to as mitochondria where respiration occurs. Tissues with high energy requirements have numerous mitochondria to provide the required energy. Examples of such tissues are the brain and muscles (Carter par. 4). Rotenone is an unscented, colorless, chemical substance that is utilized as a broad-spectrum insecticide and pesticide. It is also used to get rid of unwanted species of fish and, therefore, is a piscicide. Rotenone is a flavonoid that is found naturally in the roots of tropical plants within the pea and bean family. Like all biological reactions, enzymes are involved in the process of cellular respiration. This implies that factors that affect enzyme activity are also likely to have tremendous consequences on cellular respiration. Chemical substances that inhibit energy production in the cells are known as metabolic poisons. This paper looks at the key steps of cellular respiration as well as the effect of rotenone on the entire process of cellular respiration. Background Information Cells accumulate energy in the form of adenosine triphosphate (ATP), which is a chemical complex that comprises a nucleotide (adenine) attached to the sugar ribose and three phosphate groups. The phosphate groups in ATP are attached to the nucleoside via dehydration synthesis, which is a process where the formation of new compounds from precursor molecules is accompanied by the loss of a water molecule. The types of bonds that result from the process are referred to as phosphodiester bonds. Phosphodiester bonds are termed as ‘high-energy’ bonds because a significant amount of energy is used up during the formation of the bonds. Consequently, a considerable amount of energy is stored up in the bonds. The cleavage of these bonds through hydrolysis reactions liberates energy that is utilized in driving biological reactions. A nucleoside diphosphate and a free phosphate molecule are formed from the reaction. Therefore, this reaction can proceed in either direction and can be illustrated by the following chemical equation: ADP + ℗ ↔ ATP + H2O The process of cellular respiration allows ATP molecules to be made. Therefore, living cells can access this energy by breaking up these bonds. This same energy is made available to other cells through the transportation of ATP molecules to the cells. Sometimes it is not possible to transfer the entire ATP molecule. Therefore, the phosphate group is conveyed to another molecule, which then becomes phosphorylated, and can liberate energy by releasing the phosphate molecule. It is important to be conversant with all the steps that lead to the generation of ATP in order to comprehend the effect of rotenone on cellular respiration. The Process of Cellular Respiration The initial step in cellular respiration is glycolysis where glucose, a six-carbon molecule, is changed into two three-carbon molecules known as pyruvic acid. The initial step involves the conversion of glucose into glucose-6-phosphate, which is catalyzed by the enzyme hexokinase. Glucose-6-phosphate is then converted to fructose-6-phosphate under the influence of phosphoglucoisomerase. The resultant fructose-6-phosphate is further phosphorylated to yield fructose-1,6-bisphosphate. Subsequently, aldolase catalyzes the breakdown of fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehydes phosphate. A series of five additional reactions lead to the formation of two molecules of phosphoenol pyruvate (PEP). Pyruvate kinase then catalyzes the transfer of the phosphate groups from PEP to ADP leading to the formation of pyruvate and two molecules of ATP in addition to two water molecules and two NADH molecules. Glycolysis does not require the availability of oxygen and takes place in the cell cytoplasm. The entire glycolytic pathway consumes two molecules of ATP and generates four ATP molecules. Therefore, the net amount of energy yielded is two molecules of ATP. The chemical equation that summarizes glycolysis is as follows: Glucose + 2NAD+ + 2Pi + 2ADP → 2Pyruvate + 2NADH + 2 ATP + 2 H+ + 2 H2O Figure 1: The glycolytic pathway (Garrett and Grisham 427). Pyruvic acid from glycolysis undergoes oxidative decarboxylation to form acetyl CoA, which enters the citric acid cycle. A molecule of carbon dioxide and NADH are also formed. The enzyme pyruvate dehydrogenase complex is responsible for this reaction, which may take place in the cytosol or the mitochondria (Garret and Grisham 428). The next phase, the citric acid cycle, happens in the matrix of the mitochondria. It is also known as the Kreb’s cycle or the tricarboxylic acid (TCA) cycle. The cycle entails eight key steps. The initial step involves the reaction of acetyl-CoA with oxaloacetate to form a six-carbon compound known as citrate. Isocitrate is then formed from citrate under the influence of the enzyme citrate synthase. Isocitrate lyase subsequently cleaves isocitrate into carbon dioxide and alpha-ketoglutarate, which is then converted to succinyl CoA, then to succinic acid. Succinic acid is converted into fumarate then to fumarate and malate and ultimately to oxaloacetate. During the cycle, one molecule of glucose produces six molecules of NADH, two molecules of FADH2 as well as two molecules of ATP (Gilbert 156). Figure 2: The citric acid cycle (Gilbert 153). The third step during cellular respiration is the electron transport chain or oxidative phosphorylation where the NADH and FADH2 created from the tricarboxylic acid cycle is transformed to ATP via a sequence of chemical reactions (Briere, Benit and Rustin 20). The electron transport chain is an organization of electron carriers (cytochromes) found in the mitochondrial cristae in eukaryotes and the cell membrane in prokaryotes. The cytochromes are also referred to as complexes identified using the Roman numerals I to V. Energy from electrons is harnessed and accumulated as electrons are conveyed from one compound to the next within the series. At this point, a total of 10 NADH (six from TCA cycle and four from glycolysis) and the two FADH2 molecules have stored a total of twenty-four electrons. Oxygen functions as the eventual acceptor of electrons leading to the formation of water. The following equation summarizes the electron transport chain. 10NADH + 10H+ + 2FADH2 + 6O2 → 10NAD+ + 2FAD +12 H2O The Importance of Cellular Respiration to the Cells and the Body Cellular respiration is vital since it is the only machinery through which living cells can utilize oxygen to liberate energy from food substances. The energy produced is used to drive biological processes. Carbon dioxide and water, the resultant waste products, are released from the process. Effects of Rotenone to the Body Rotenone disrupts cellular respiration by opposing the electron transport in mitochondria through the blockage of the enzyme NADH ubiquinone reductase (NADH dehydrogenase) that is responsible for the reduction of complex I (Golden 2; Gilbert182). This makes oxygen unavailable for cellular respiration and prevents the utilization of oxygen by living organisms. Therefore, rotenone brings about death due to tissue anoxia by impeding the uptake of oxygen at the cellular point. The lack of oxygen in the cells triggers anaerobic respiration, which spawns large amounts of lactic acid that lower the pH of blood. Recent studies also show that rotenone also induces cell death by triggering apoptosis in mitochondria (Li et al. 8516). Thus, while cellular respiration attempts to utilize oxygen for production of energy within cells, rotenone acts as an antagonist to cellular respiration. Works Cited Briere, Jean-Jacques, Paule Benit and Pierre Rustin “The Electron Transport Chain and Carcinogenesis.” Cellular Respiration and Carcinogenesis. Eds. Shireesh Apte and Rangaprasad Sarangarajan. New York, NY: Humana Press, 2009. 19- 32. Print. Carter, Janet Stein 2014. Cellular Respiration. Web. 11 April 2014. . Garrett, Reginald H and Charles Grisham. Biochemistry 5nd ed. 2012. USA: Brooks & Cole. Print. Gilbert, Hiram F. Basic Concepts in Biochemistry. 2nd ed. 2000. New York, NY: McGraw Hill. Print. Golden, Mike 2011, Chemicals and the Application of the Proposed Action. Pdf file. 11 April 2014. . Li, Nianyu, Kathy Ragheb, Gretchen Lawler, Jennie Sturgis, Bartek Rajwa, Andres J. Melendez, and Paul J. Robinson. “Mitochondrial Complex I Inhibitor Rotenone Induces Apoptosis through Enhancing Mitochondrial Reactive Oxygen Species Production.” The Journal of Biological Chemistry 278.10 (2003): 8516 –8525. Print. Read More