Exercise 4

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CH2 COOH – – COOH – CH2 H–C COOH – COOH – C–H – – CH2 COOH – – HO–C–H COOH – CH2 COOH – – C–O – COOH – Exercise 4.1 CHEM1130 Answers are in bold Lesson 30: Energy Metabolism 1. Describe these phases in energy metabolism, giving products of each phase. (3 pts) (a) Citric acid cycle Oxidizes acetyl-CoA to CO 2 ; Reduces NAD + to NADH and FAD to FADH 2 ; and makes GTP. (b) Electron transport chain Oxidizes NADH to NAD + and FADH 2 to FAD; Reduces O 2 to H 2 O; Produces a concentration gradient of H + ions across the inner mitochondrial membrane. (c) Oxidative phosphorylation ATP is produced from ADP and HPO 4 2- , by using mechanical energy, generated from the flow of H + ions back through the inner mitochondrial membrane. 2. Which steps of the citric acid cycle are regulated, and how are they regulated? The 3 irreversible steps of the citric acid cycle are regulated. These steps are regulated by the cell’s need for energy: ATP and NADH are allosteric inhibitors; ADP is an allosteric activator. 3. In the following reactions from the citric acid cycle use curved arrows to identify the other substrates required and any other products formed in each enzyme reaction. 4. Show the flow of electrons between the components of the electron transport chain, as given below, from NADH and FADH 2 to O 2 . CoQ Complex I Complex II Complex III Complex IV Cytochrome c FAD FADH 2 H 2 O NADH NAD +

FADH2 NADH Complex I Complex II Cytochrome c Complex III CoQ Complex IV O2 Exercise 4.1 CHEM1130 Answers are in bold 5. Contrast substrate-level phosphorylation and oxidative phosphorylation. Substrate-level phosphorylation makes ATP by transfer of phosphate from a phosphorylated substrate to ADP. Oxidative phosphorylation makes ATP by reversing the hydrolysis of ATP using a [H + ] gradient with ATP synthase. 6. Briefly describe proton-motive force and rotational catalysis in ATP synthesis. Proton-motive force is the energy provided by the flow of H + ions across the inner mitochondrial membrane down a H + ion concentration gradient. Rotational catalysis is the process that uses rotational kinetic energy for changing the shape of ATP synthase, making ATP from ADP and phosphate. 7. Based upon the conversion of 1 NADH = 2.5 ATP, 1 FADH 2 = 1.5 ATP and 1 GTP = 1 ATP, show the calculation of overall yield of ATP from 1 Acetyl-CoA molecule. Oxidation of 1 acetyl-CoA produces 3 NADH, 1 FADH 2 and 1 GTP. Using the conversion rates, the number of ATP produced from 1 acetyl-CoA is = (2.5 ATP/NADH × 3 NADH) + (1.5 ATP/FADH 2 × 1 FADH 2 ) + (1 ATP/GTP × 1 GTP) = 7.5 ATP + 1.5 ATP + 1 ATP = 10 ATP from 1 acetyl-CoA Lesson 22: Carbohydrate Metabolism – part 1 8. Describe the purpose of glycolysis, and list the products of glycolysis. Glycolysis is the major catabolic pathway for obtaining energy from glucose. It produces 2 pyruvates, 2 NADH and 2 ATP from each molecule of glucose. Pyruvate may be oxidized to acetyl-CoA or reduced to lactate. 9. Which two products made from pyruvate in the absence or presence of oxygen? Why must pyruvate be reduced for making ATP without oxygen? In the presence of oxygen, pyruvate is oxidized to acetyl-CoA. In absence of oxygen, pyruvate is reduced to lactate. This reduction is coupled to the oxidation of NADH to NAD + . NAD + is needed for continuing glycolysis.

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