Cellular Respiration: A Biological Process

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Gluskin 6
              This experiment attempts to answer the question of whether an increase in a succinate concentration (a component of the Krebs cycle) will lead to an increased rate of cellular respiration within a cell. We measured the amount of electrons given off by the succinate to fumerate redox reaction by using DPIP. DPIP is an electron acceptor that takes the place of FAD by accepting the electrons and turning from its oxidized blue state to its reduced clear state. We had three tubes with varying concentrations of succinate and measured the transmittance of each over a half hour period to determine whether more succinate led to more DPIP being reduced. The results showed that the tube with no succinate (no reaction) had an average increase in percent transmittance from 58.13% to 59.97%. The tube with the least succinate raised in transmittance from 59.1% to 73.27%. The tube with the highest succinate concentration raised from 58.27% to 85.03%. This data supports my hypothesis that an increased amount of succinate will lead to a higher rate of cellular respiration. The tubes with more succinate gave off more electrons, which reduced more of the DPIP, raising the transmittance. Introduction:

              Cellular respiration is a biological process used by most organisms, enabling them to produce ATP in large amounts, which can be used to provide energy for cells (Campbell, 2008). It involves three processes: glycolysis, Krebs cycle and the electron transport chain. All of these three produce ATP in some way and work ideally under aerobic conditions (in the presence of oxygen). It can also function in anaerobic conditions (lacking oxygen), in a process called fermentation. However, this is much less effective since it leaves out the greatest producer of ATP, the electron transport chain (Campbell, 2007). This experiment focuses specifically on one step in the Krebs cycle, a series of eight catalytic reactions (Wrischnik, 2010). It involves oxidation, the losing of electrons, and reduction, the gaining of electrons. In the cycle, a compound gives off electrons to an oxidized carrier (NAD+ and FAD) in order to make it reduced (NADH and FADH2). It can then transport then electrons to the next step and continue cellular respiration (Wrischnik, 2010). The question that this lab attempts to answer is how much the concentration of one of these compounds in the cycle affects the rate of cellular respiration. In order to do this, we used one specific part of the cycle, the conversion of succinate to fumerate. This involves the compound succinate giving protons and electrons to FAD and being converted to fumerate as a result (Wrischnik, 2010). One way to determine the rate of cellular respiration is by measuring the amount of protons and electrons given off by succinate in the cycle. However, since there is no easy way to measure the amount of FADH2 produced, we used a substance called DPIP (di-chlorophenol-indophenol). Oxidized DPIP is a deep blue color, but when it accepts electrons or protons, it turns colorless (Wrischnik, 2010). When placed in the presence of succinate, it will absorb all of the electrons meant for the electron carriers and become reduced and colorless. By measuring the absorbance of DPIP with either a high or low succinate concentration, we determined how many electrons were given off, and therefore how much of the reaction was occurring (Wrischnik, 2010). If the amount of light transmitted through the DPIP is low, this means that the DPIP is absorbing a lot of light and the DPIP is fairly oxidized. In this case the reaction is not taking place in high abundance. On the other hand, if the transmittance is high, then the DPIP is absorbing little light and is in its clear, reduced state. This would mean that a great deal of the reaction is taking place (Wrischnik, 2010). The solution of DPIP and succinate will take place with a prepared mitochondrial suspension created from pulverized...
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