Cellular Respiration Review.pdf - 2.2 Recap Cellular Respiration Explain the relationship between anabolic and catabolic reactions Describe how

Cellular Respiration Review.pdf - 2.2 Recap Cellular...

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Unformatted text preview: 2.2 Recap: Cellular Respiration • • • • • • • • • • • • • Explain the relationship between anabolic and catabolic reactions. Describe how oxidation / reduction reactions are used in biochemical pathways to transport electrons. Explain the role of electron carrier molecules and why they shuttle electrons around the cell. Identify the location of glycolysis, fermentation, pyruvate oxidation, citric acid cycle, and oxidative phosphorylation. Justify why glycolysis is considered an evolutionary significant pathway. Explain the relationship between glycolysis and fermentation. Describe the fate of pyruvate in aerobic respiration. Explain the regulation of aerobic respiration and how these pathways link to other metabolic pathways. Describe how the electron transport chain builds a proton gradient and how it is used to form ATP by chemiosmosis. Explain why oxygen is the final electron acceptor in aerobic respiration. Compare and contrast the efficiency of anaerobic and aerobic respiration. RedOx-­‐Redox reactions are paired reactions involving the transfer of electrons ◦ Oxidation-­‐ loss of electrons ◦ Reduction-­‐ gain of electrons ▪ Remember this! Leo the lion goes GER ▪ LEOGER: Lose Electrons Oxidation Gain Electrons Reduction ▪ The electron donor that gives electrons to the molecule being reduced is the reducing agent. ▪ The electron acceptor that accepts electrons given by the molecule being oxidized is the oxidation agent. ▪ This means that the reducing agent is being oxidized while the oxidizing agent is being reduced. ◦ Respiration ▪ Respiration can be viewed as a series of redox reactions. • C6H12O6 is oxidized → CO2 and O2 is reduced → H2O • As electrons move from organic compounds towards oxygen, the electrons lose their own potential energy as they create a hydrogen ion gradient. • Electrons to electron carriers. ◦ NAD+ is reduced to NADH. ◦ Electron carriers are used to move electrons through the electron transport chain which moves the electrons to O2 in steps that convert energy into a hydrogen ion gradient. This hydrogen ion gradient is what drives forward ATP. Stages of Cellular Respiration ◦ 1. Glycolysis; the oxidizing of glucose to pyruvate. Glucose is essentially cut in half. This process costs an initial investment of 2 ATP but the oxidation of glucose also produces 2 ATP and 2 NADH. This process occurs in the cytosol and is highly conserved in species. O2 is not required for glycolysis; if oxygen is present, then pyruvate will move on to the rest of respiration. ▪ Glycolysis is highly conserved; meaning that it is found in the earliest species and has been retained in their ancestors. For this reason, it is evolutionarily significant. If you want to think about it: If the earliest species only used glycolysis to extract energy from organic molecules, then we may be able to study evolution by seeing how species evolved their post-­‐glycolysis steps. With a common glycolysis-­‐only ancestor as our starting point, we can create a tree of the • • • • evolution of cellular respiration pathways. ◦ 2. Pyruvate oxidation; pyruvate enters the mitochondrion and then is converted to Acetyl-­‐CoA. This step produces 2 NADH. ◦ 3. Citric Acid Cycle/Krebs Cycle-­‐ Acetyl CoA is oxidized, transferring electrons to electron carriers. 1 Acetyl CoA produces 3NADH, 1 FADH2 and 1 ATP. So 1 glucose produces 6 NADH, 2 FADH2 and 2 ATP. This step occurs in the matrix of the mitochondria. ◦ 4. Oxidative phosphorylation/Electron Transport Chain-­‐ So what exactly are we going to do with all of these electron carriers? The final step of Cellular respiration occurs in the matrix of the mitochondria. The electron carriers are sent through different enzyme complexes which remove the electrons from the electron carriers and eject the hydrogens out into the inner membrane space. The end result is that the energy from the electrons, stored in the electron carriers, is released to form a hydrogen ion gradient. ▪ In this step, we also see that oxygen is the last electron carrier; cytochrome a3 passes the last electrons from the NADH or FADH2s to oxygen which uses them to form H2O. If we look at the balanced equation for the breakdown of glucose, this is where the H2Os are produced. (the balanced equation being C6H12O6 + 6O2 → 6 CO2 + 6H2O ATP Synthase ◦ ATP synthase is a molecule that adds a phosphate group to ADP to produce ATP. It uses energy stored in the form of a hydrogen ion gradient to run. We can think of the hydrogen ion gradient as a river; the innermembrane is uphill while the matrix is downhill. The hydrogen ions flow downhill (from high concentration to low concentration) into the matrix. Think of ATP synthase as a watermill; it uses the power of the hydrogens flowing down to do work. Fermentation ◦ Fermentation harvests chemical energy without oxygen and without an electron transport chain. It is an anaerobic method of extracting energy; no need for oxygen! ▪ Glycolysis produces pyruvate as well as ATP. To get more energy from the glucose, we oxidize the pyruvate. What pyruvate is converted to defines the type of fermentation. There is alcohol fermentation in which pyruvate is converted to ethanol. There is also lactic acid fermentation in which pyruvate is converted to lactate. ▪ Yeast is used for alcoholic fermentation in order to produce bread and beverages. Lactic acid fermentation is used in the fungi and bacteria that make cheese and yogurt. It is also used in human muscles when oxygen is being used by the muscles faster than it can be acquired. Pyruvate in Fermentation vs Aerobic Respiration ◦ It can be hard to keep track of all of the molecules involved in these pathways. Relax, you won't need to until you take biochemistry. For AP biology, it is sufficient to understand what is happening without keeping an exact count of the molecules. ◦ Since Aerobic and Anaerobic respiration both begin with glycolysis, we can consider the pyruvate as the differentiation point for both of these processes. ◦ In fermentation, the carbons of pyruvate are used to produce another 2 carbon molecule; lactate or alcohol usually. In aerobic Respiration, the pyruvate is broken down and eventually CO2 molecules are released. ◦ Because of the electron transport chain/oxidative phosphorylation, Aerobic respiration produces much more ATP per glucose molecule consumed than fermentation/glycolysis. Thus, aerobic respiration is much more efficient for producing ATP. ATP Regulation ◦ Feedback inhibition is the most common form of regulation in a cell; to be efficient, the cell does not produce more of what it already has. So, the end product a reaction often acts as an inhibitor for the reaction. This is the case for ATP production! If a cell has lots of ATP, then respiration will slow down. If a cell has not much ATP< then respiration will speed up. ...
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