Glycolysis - Study guide PDF

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Lecture 16– Glycolysis 1) A. What is an oxidation-reduction reaction? (Pg. 166, 1st column, 1st paragraph) In a redox reaction, the loss of electrons from one substance is called oxidation, and the addition of electrons to another substance is known as reduction. B. In the oxidation-reduction reaction shown below, which reaction component is the reducing agent and which is the oxidizing agent? Reducing agent C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat) Oxidizing agent 2) A. How is the formation of a polar covalent bond an example of an oxidationreduction reaction? (Pg. 166, paragraph 3, sentence 1 and Figure 9.3) Not all redox reactions involve the complete transfer of electrons from one substance to another; some change the degree of electron sharing in covalent bonds. B. How does the potential energy in an electron relate to its association with an electronegative atom? (Pg. 166, paragraph 5) An electron loses potential energy when it shifts from a less electronegative atom towards a more electronegative one. 3) What are the roles of dehydrogenase and the coenzyme nicotinamide adenine dinucleotide (NAD+) in catabolic pathways? (Pg. 167, paragraphs 2-3) Enzymes called dehydrogenases remove a pair of hydrogen atoms from glucose and other organic molecules in food, thereby oxidizing it. The dehydrogenase delivers the 2 electrons along with one proton to its coenzyme, NAD+, forming NADH. The other proton is released into the surrounding solution. 4) A. Energy from electrons carried by NADH (and FADH2) is harvested through a controlled release as they travel toward an electronegative oxygen atom. How does the controlled release of energy occur? (Pg. 168, paragraph 2 sentences 1-4 and Fig. 9.5b) Electron transfer from NADH to oxygen is an exergonic reaction with a free energy change of -53 kcal/mol (-222 kJ/mol). Instead of this energy being released and wasted in one explosive step, electrons cascade down the chain from one carrier molecule to the next in a series of redox reactions, losing a small amount of energy with each step until they finally reach oxygen, the terminal electron acceptor, which has a great affinity for electrons. Each “downhill” carrier is more electronegative than, and thus capable of oxidizing its “uphill” neighbor, with oxygen at the bottom of the chain. Therefore, the electrons transferred from glucose to NAD+ which is thus reduced to NADH, fall down an energy gradient in the electron transport chain to a far more stable location in the electronegative oxygen atom. 5) Define substrate-level phosphorylation. (One sentence, Pg. 169, Fig. 9.7) When an enzyme transfers a phosphate group from a substrate molecule to ADP rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation. 6) A. How does the energy investment phase of glycolysis differ from the energy pay-off phase? (Describe the products of glycolysis in your answer.) (Pg. 170, Fig. 9.8) During the investment phase, the cell actually spends ATP. During the payoff phase, ATP is produced and NAD+ is reduced to NADH. The net energy yield from glycolysis per glucose molecule is 2 ATP plus 2 NADH

B. What is the fate of the final product of glycolysis? (Pg. 171, 2nd paragraph, and Fig. 9.10) Upon entering the mitochondrion via active transport pyruvate is first converted to a compound called acetyl coenzyme A (acetyl CoA). The acetyl group enters the citric acid cycle. 7) What is the donor of the H+ ion donated to NAD+ when pyruvate enters the mitochondrial matrix? (Lecture notes and Slide 15) Thiamine pyrophosphate (TPP) – Vitamin B1 – coenzyme of pyruvate dehydrogenase. 8) List four vitamins that play a direct role in glycolysis and the citric acid cycle. (Lecture notes and Slides 14 – 15) Vitamin B5, Vitamin B1, lipoyllysine Lecture 17 - The citric acid cycle and oxidative phosphorylation 1) A. Where does the citric acid cycle occur? (Lecture notes) Mitochondrion B. What are all of the products of the citric acid cycle and how are they used? (Pg. 173, Fig. 9.12; Pg. 172, second column, paragraph 3) 3 NAD+ are reduced to NADH. FAD accepts 2 electrons and 2 protons to become FADH2. In many animal tissue cells, a GTP molecule is produced by substrate level phosphorylation. The GTP may be used to make an ATP molecule or to directly power work in a cell. Each glucose gives rise to two molecules of acetyl CoA that enter the cycle. The total yield from per glucose from the citric acid cycle turns out to be 6 NADH, 2 FADH 2, and 2 ATP. 2) A. Describe the oxidation-reduction that the components of the electron transport chain undergo as electrons are accepted and donated. Include in your answer the direction of electronegativity as well as the separate roles of the components of the electron transport chain. The ETC is a collection of molecules embedded in the inner membrane of the mitochondrion in eukaryotic cells. Most components of the chain are proteins which exist in multiprotein complexes. Tightly bound to the proteins are prosthetic groups – nonprotein components such as cofactors and coenzymes essential for the catalytic functions of certain enzymes. During electron transport, carriers alternate between reduced and oxidized states as they accept and then donate electrons. A component becomes reduced when it accepts electrons from its uphill neighbor which has a lower affinity for electrons (less electronegative). It returns to its oxidized form as it passes electrons to its downhill more electronegative neighbor. Electrons acquired from glucose by NAD+ during glycolysis and the citric acid cycle are transferred from NADH to the first molecule of the ETC in complex 1. This molecule is a flavoprotein due to its prosthetic group called a Flavin mononucleotide. The flavoprotein returns to its oxidized form as it passes electrons to Fe-S (an iron-sulfur protein). Fe-S then passes electrons to a compound called ubiquinone. Ubiquinone is a small hydrophobic molecule and is not a protein. It is individually mobile rather than residing in a particular complex. Most of the remaining electron carriers between ubiquinone and oxygen are proteins called cytochromes. Their prosthetic group is called a heme group and has an iron atom that accepts and donates electrons. The last cytochrome passes the electrons to oxygen which also picks up a pair of hydrogen ions (protons) from the aqueous solution neutralizing the -2 charge of the added electrons and forming water.

3) How is electron transport related to ATP synthesis? Include the terms proton-motive force and chemiosmosis in your answer. (Pg. 177, paragraph 1, sentences 5-7 and paragraph 2, sentences 1-2 and Fig. 9.15) Establishing the H+ gradient is a major function of the ETC. The chain is an energy converter that uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across the membrane from the mitochondrial matrix to the intermembrane space. H+ has a tendency to move back across the membrane diffusing down its gradient. ATP synthases are the only sites that provide a route through the membrane for H+. The passage of H+ through ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ADP. Thus, energy stored in an H+ gradient across a membrane couples the redox reactions of the ETC to ATP synthesis. At certain steps along the chain, electron transfers cause H+ to be taken up and released into the surrounding solution. In eukaryotic cells, the electron carriers are spatially arranged in the inner mitochondrial matrix and deposited in the intermembrane space. The H+ gradient that results is referred to as a proton-motive force, emphasizing the capacity of the gradient to perform work. The force drives H+ back across the membrane through the channels provided by ATP synthases. Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work. 4) How does the ATP synthase complex generate ATP? (Pg. 175, Fig. 9.14) ATP synthase is an enzyme that makes ATP from ADP and inorganic phosphate. It works like an ion pump running in reverse. Ion pumps use ATP as an energy source to transport ions against their gradients. ATP synthase uses the energy of an existing ion gradient to power ATP synthesis. The power source is a difference in concentration of H+ on opposite sides of the inner mitochondrial membrane. This is called chemiosmosis. 5) A. What is the total number of ATP molecules extracted from a single molecule of glucose by cellular respiration? Indicate the number of ATP molecules from each step and how they were produced. (Pg. 177, Fig. 9.16) Glycolysis – 2 ATP by substrate level phosphorylation, Citric Acid Cycle – 2 ATP by substrate level phosphorylation, Oxidative Phosphorylation (Electron Transport and Chemiosmosis) – about 26 or 28 ATP by oxidative phosphorylation. Total – 30 or 32 ATP. B. What is the efficiency of cellular respiration when the amount of chemical energy in a glucose molecule is 686 kcal/mol and the amount of chemical energy in each molecule of ATP is 7.3 kcal/mol? (Pg. 178, second column, paragraph 1) 34% of potential chemical energy in glucose has been transferred to ATP. Even the most efficient automobile converts only about 25% of the energy stored in fuel to energy that moves the car. 6) A. What determines whether yeast or bacteria will use the fermentation or oxidative phosphorylation pathways? (Pg. 179, paragraph 1, sentences 2-3) When oxygen is unavailable to pull electrons down the transport chain, there are two mechanisms by which certain cells can oxidize organic fuel and generate ATP without the use of oxygen. B. What is fermentation? (Pg. 180, paragraph 2, sentence 1, and paragraph 4, sentence 1) Fermentation is a way of harvesting chemical energy without using oxygen or any ETC. C. How do alcohol and lactic acid fermentation differ? (Pg. 180, Fig. 9.17)

In alcohol fermentation pyruvate is converted to ethanol in two steps. In lactic acid fermentation pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of CO2. 7) A. How is ATP synthesized in muscle cells during a strenuous workout? (Pg. 180, 2nd column, final paragraph) Human muscle cells make ATP by lactic acid fermentation when oxygen is scarce during strenuous exercise when sugar catabolism for ATP production outpaces the muscles supply oxygen from the blood. Cells switch from aerobic respiration to fermentation. B. What is the source of muscle pain after an exercise session? (Pg. 181, paragraph 1, final sentence) The pain after exercise is due to trauma to small muscle fibers. 8) At what point do the digestion products from fats and proteins enter the cellular respiration pathway? Indicate the structural modifications that are critical for entry into the pathway. (Pg. 182, 2nd column, paragraphs 1-2, and Fig. 9.19) Before amino acids can be used, the amino groups must be removed through deamination. Nitrogenous waste is excreted as urine. A metabolic sequence called beta oxidation breaks fatty acids down into 2-carbon fragments which enter the citric acid cycle as acetyl CoA. 9) How does the enzyme Phosphofructokinase regulate cellular respiration? (Pg. 183, Fig. 9.20 and Pg. 184, paragraph 1) It has specific sites for inhibitors and activators, and is inhibited by ATP but stimulated by AMP which the cell derives from ADP. As ATP accumulates, inhibition of enzyme slows down glycolysis. Enzyme becomes active again as cellular work converts ATP to ADP and AMP faster than ATP is being regenerated. Its also sensitive to a product of citric acid cycle to sync the cycles....