Biology 141, Fall 2013 Exam 1 Study Questions

(080813) 20. Assume a cell is respiring aerobically and is using glucose as an energy source. What is the ultimate fate of each of the 6 carbon atoms in a glucose molecule that begins the aerobic pathway (i.e., what happens to each of the carbons and where does it happen)? the glucose carbon (6C) will break into two pyruvates (3C each) then one carbon will be lost in the link reaction that releases a CO2 molecule and adds a CoA to the 2 Carbon molecule forming Acetyl CoA. The Acetyl CoA molecule enters the Kreb Cycle. It first gets associated with oxaloacetate (4C) that releases the CoA. Two CO2 molecules are released after the reduction of 2 NAD+ to 2 NADH. Which leaves us with a new Oxaloacetate molecule that will enter the kreb cycle again. 21. Where are the enzymes that convert pyruvate to acetyl-CoA found? Where are the enzymes of the Krebs Cycle found (i.e., in which compartment of which organelle)? The enzyme that converts pyruvate to Acetyl-CoA is Pyruvate dehydrogenase in the link reaction in the cytoplasm. The enzymes of the Krebs cycle takes place in the matrix of Mitochondria. 22. In aerobic respiration, does atmospheric oxygen combine chemically with carbon to produce CO2? If your answer is yes, please explain. If it is no, please explain. No, the CO2 molecules are produced by chemical reactions that happen during the cellular respiration (ex: Krebs cycle) while the atmospheric oxygen is used for the electron transport chain as the final electron receiver. 23. Where do the "high energy electrons" come from that enter the electron transport system of mitochondria? Specifically, what chemical compound (or compounds) is(are) the immediate source of the electrons injected into the mitochondrial electron transport system? Where do these electron-donating compounds gain their electrons? The high-energy electrons come from the oxidized molecules that released earlier during the krebs cycle the link reaction… NADH and FADH2 are oxidized and the energy is used to produce ATP. They gain their electrons from the chemical reactions that happened in the cell 24. Cyanide acts by blocking the flow of electrons in the electron transport system in mitochondria. What happens to ATP formation and oxygen consumption in mitochondria when cells are poisoned with cyanide? I.e., do the rates of oxygen consumption and ATP formation increase, or decrease, or remain constant? Which does what? ATP formation and oxygen consumption in mitochondria when cells are poisoned with cyanide

decreases because the electrons that are blocked are needed to form the oxygen hence less oxygen consumption 25. List all of the products of glycolysis in decreasing order of the amount of chemical energy they contain as single molecules. [Note: Intermediate compounds are not products.] 2 pyruvate molecules 2 NADH molecules 2 ATPs 26. Can fatty acids be used as a source of energy in anaerobic respiration (i.e., in fermentation)? Why or why not? [Hint: examine Fig. 9.27, p. 169] No, the break down of fatty acids require energy in form of ATP that needs oxygen to work. Therefore it is not possible for fatty acids to be used as a form of energy in anaerobic respiration where oxygen is not present. 27. Can proteins be used by your cells as a source of chemical energy to make ATP? Explain. No, proteins are needed as functional proteins to help in the process of building ATP, and proteins can break down ATP. 28. Are NAD+ and FAD enzymes? If your answer is yes, describe the biochemical reactions catalyzed by these enzymes. If your answer is no, then what type of compounds are they and what is their function? No , NAD+ and FAD are electron carriers throughout reduction and oxidation reactions. So they transport electrons or H protons to different locations in the cell to unable the different functions that has to be done. 29. When oxygen is unavailable, some cells use anaerobic (fermentation) pathways to make ATP. Another textbook says regarding fermentation: "The final steps serve only to regenerate NAD+." What does this statement mean? Explain using examples of specific fermentation pathways. Fermentation makes lactic acid and alcohol from pyruvates made in glycolysis. at the same time NADH is converted back into NAD+ so that glycolysis can happen again. 30. Which molecule contains more energy stored in its chemical bonds? Rank in order of decreasing chemical energy content: a fatty acid molecule, a molecule of glucose, a molecule of NADH, a molecule of ATP, a molecule of FADH2, a molecule of acetyl-CoA, a molecule of pyruvate? [Hint: think of ATP as the chemical energy exchange equivalent of a one-dollar bill. How many ATPs can you get in exchange for a single FADH2 molecule? What does that imply about the chemical energy content of the FADH2 molecule?] Glucose Fatty acid Pyruvate

NADH FADH2 acetyl-CoA ATP 31. Textbooks often refer to oxygen as the "final electron acceptor." What does this statement mean? Oxygen is the final electron acceptor. The low-energy electrons that came from the electron transport chain are taken up by oxygen.