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Mattie Knebel Kyler Salazar Jared Hansen Biology 1610 Sperry March 5, 2013 Writing Assignment #2 Importance of Cellular Respiration Animals and humans share the same characteristic of being dynamic, meaning they are constantly at work in their bodies. A lot of these works are fueled by the molecule ATP, which is the end product of cellular respiration along with 3 cycles. In cellular respiration, a cell inputs glucose and outputs a total of 30-32 ATP molecules which can be used for any actions in the cell. The three aerobic reaction cycles that partake in cellular respiration are Glycolysis, the Citric Acid Cycle, and Oxidative Phosphorylation. There is one anaerobic reaction cycle, anaerobic meaning the lack of Oxygen, called fermentation. The first cycle, Glycolysis, inputs a 6C glucose molecule, breaks it down, and outputs two separate 3C Pyruvate. In order to achieve Glycolysis’ output, it goes through a series of reactions. The first being Glucose converted to Glyceraldehyde-3 Phosphate. This step is an anabolic reaction, which requires 2 ATP in order to react. Next, NAD+ comes in and picks up 2 electrons in the form of Hydrogen ions and form NADH. The energy released from this reaction is then used to apply a phosphate group to both of the G3P molecules, which is then rearranged to make a 3 carbon molecule. After this, ADP is added and takes the phosphate group, leaving only the two separate 3 Carbon molecules called Pyruvate. This cycle takes place in the cytosol, located just outside of the mitochondria. This process has a net gain of 2 ATP which is then carried on to the next cycle. Diagram A, which can be found on our flow chart, shows this process. The 2nd cycle, the Citric Acid Cycle, is the production of NADH and FADH2 for Oxidative Phosphorylation. Before this can happen, the cell must go through the linker step. In the linker step, Coenzyme A is added to the 3C Pyruvate from Glycolysis. Oxygen is also added in this step producing a Carbon Dioxide molecule. After this, the Citric Acid Cycle can begin. Acetyl CoA enters into the citric acid cycle and is attached to the 4C molecule Oxaloacetate. The CoA is then released and a 6C molecule called citrate is left behind. After Citrate is formed, it is broken down into a 5C molecule using Oxygen which then produces a CO2 molecule. NAD+ then comes along and takes 2 electrons producing NADH. Next, Oxygen is used to break down the 5C molecule into a 4C molecule producing another CO2 molecule. NAD+ picks up two more electrons and produces NADH. FAD+ also uses two hydrogen ions in this step to produce FADH2. When NAD+ is turned into NADH, it releases energy that is then used to combine a phosphate group to an ADP molecule to produce 1 ATP molecule. After this, the 4C Oxaloacetate can be used for the second Acetyl CoA molecule, created from Glycolysis, and repeat the cycle to produce another ATP molecule. This process, which can be seen in figure B of the flow chart, occurs in the mitochondrial matrix and has a net gain of 2 ATP. The 3rd and final cycle, Oxidative Phosphorylation, outputs the most ATP of all the cycles (26-28) and takes place in the inner mitochondrial membrane. There are 2 main steps to this cycle, the Electron Transport Chain (ETC) and Chemiosmosis. In the ETC, NADH gives up its electrons producing a large amount of energy. This energy that the electrons lose is then used to pull H+ ions out of the mitochondrial matrix and into the intermembrane layer. In the ETC, the electrons are attracted to the highly electronegative oxygen at the end of the chain, where the electrons combine with oxygen to produce H2O. Once the Hydrogen’s are all transported out into the intermembrane space, Chemiosmosis can occur. In this step, H+ ions will diffuse back into the mitochondrial matrix if ATP Synthase is present in the membrane. As the ions diffuse back into the matrix, they release their energy. ATP Synthase utilizes this energy to combine a phosphate group to ADP. Our body could not go through these aerobic cycles if we did not obtain a diet full of Carbon. Cellular respiration cannot happen without carbon. Along with carbon, these cycles explained above also require Oxygen. Yes, the cell can still go through Fermentation to produce Lactic acid without the presence of Oxygen; However, this process only yields 2 ATP’s which is a very small amount compared to aerobic cycles and the amount of ATP our cells need daily in order to properly function. Plants utilize light energy to produce chemical energy. This process in which CO2 and H2O are used to produce Glucose and Oxygen is referred to as Photosynthesis. Plants use this process with the addition of cellular respiration to produce acceptable amounts of NADH and ATP that we, humans, can later consume into our bodies to help aid the appropriate cellular respiration in our cells. Animals and plants are greatly codependent of each other. Animals provide plants with CO2, which plants then use to form Oxygen and Glucose. This sugar and oxygen is essential to humans and animals to be able to produce energy and CO2. This recurring balanced system we participate in is what we call life. The main misconception that was seen in my group over the course of writing this paper was the confusion of how many ATP molecules Glycolysis produces. Yes, it is true that 4 ATP’s are made in the Energy payoff phase, but the Energy Investment phase of this cycle requires the use of 2 ATP’s. So although 4 ATP’s are created, 2 are used, making Glycolysis have an overall net gain of 2 ATP’s. The only other misconception was the question of where each of these cycles occurred. We were able to research and conclude that Glycolysis occurs in the cytosol, the Citric Acid Cycle in the mitochondrial matrix, and Oxidative Phosphorylation in the inner mitochondrial membrane.