Question

(35 pts) The overall objective of metabolism is to generate energy in the form of ATP by oxidizing carbon and reducing oxygen. (a) (2 pts) Write chemical reaction for the only oxidation step in glycolysis with full chemical structures of the reactant(s) and product(s), list the name(s) of the enzyme(s) and cofactor(s) involved in the equation. Indicate which carbons are oxidized in the chemical structures (b) (8 pts) Write the chemical reactions for all oxidation steps for citrate acid cycle with full chemical volved in the equati structures for reactants and products, list all enzymes and cofactors in Indicate which carbons are oxidized in the chemical structures. pts) Write the chemical equations with full chemical structures and names of enzymes and rs involved for the steps that CO2 is produced in citric acid cycle. Circle or highlight withirn which carbons become CO2. Do these carbons come from the acetyl group the chemical structures entering the citric acid cycle? Explain. (d) (4 pts) Do these oxidation reactions in citric acid cycle involve molecular oxygen (02)? If yes, indicate how O2 is involved. If no, explain why these steps are strongly inhibited by anaerobic condition? (e) (3 pts) Where d oes oxygen is reduced? What is the product for oxygen reduction? You only need enoess and what organelle and protein complex, and write down the formula cf the product (O (12 pts) Summary how (a) glycolysis, (b) citric acid cyele, a and (c) oxidative phosphorylation each contributes to the overall objective of metabolism (generating energy, oxidizing carbon, arnd reducing oxygen).

Answer 1

a. There is one step in glycolysis where glyceraldehyde-3-phosphate is oxidized(and simultaneously phosphorylated) to 1-3-biphosphoglycerate by the enzyme glyceraldehyde phosphate dehydrogenase. In this reaction, nicotinamide adenine dinucleotide (NAD) is the oxidizing agent.

b. Oxidation steps in the citric acid cycle-

Isocitrate is oxidized to alpha-ketoglutarate yielding NADH, H+ and CO2. The enzyme used is isocitrate dehydrogenase.

Alpha-ketoglutarate is oxidized to succinyl CoA with the formation of NADH, H+ and CO2. This step is almost identical to pyruvate oxidation. The enzyme used is alpha-ketoglutarate dehydrogenase.

Succinate is oxidized to fumarate with the formation of FADH2. The enzyme used is succinate dehydrogenase.

Malate is oxidized to oxaloacetate with the formation of NADH +H+ which can react with acetyl CoA and begin the cycle. The enzyme used is malate dehydrogenase.

Acetyl CoA CoA Six-carloon mo lecule formed from acetyl CoA oxaloacetate Fouur-carbon acceptor molecule regenerak d each cycle) 0000 Oaloacetale One caroo ar NADH NADH CO secand Corbon lost aS CO7 NADt NADH + CO o0oo Reduce eleotron carner GDP, NADH ergy -carryna 峁く2-molecule eguivalent FAD to ATP

c.

IH Hd-C-o +NAD NADH intermediate isocitrate alpha-ketoglutarate intermediate

The enzyme used is - isocitrate dehydrogenase

alpha-ketoglutarate succinyl CoA +NAD + CoA > NADHCO2 + H OA

In this step, alpha-ketoglutarate dehydrogenase enzyme is used. These two steps yield CO2 molecules in the Citric Acid cycle.

d. No molecular oxygen is not required in the Citric acid cycle. It acts as a final electron acceptor in the electron transport chain. Without oxygen, the electron transport chain becomes jammed with electrons. Consequently, NAD cannot be produced, thereby causing glycolysis to produce lactic acid instead of pyruvate, which is a necessary component of the Krebs Cycle. Thus, the Krebs cycle is heavily dependent on oxygen but indirectly.

e. Oxygen is needed for electron transport chain that leads to oxidative phosphorylation i.e formation of proton gradient through the flow of electrons via electron carriers and ultimately the liberation of energy used for the synthesis of ATP.

Electron Transport Chain Intermembrane space Cyt c IV 2e- FADH2 NADH FAD H2O 2H 1/2022 NAD+H Mitochondrial matrix Inner mitochondrial membrane

f.

Overview of Cellular Respiration NADH High-energy electrons carried by NADH NADH FADH2 an Stage 1 Stage 3 Stage 2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) GLYCOLYSIS CITRIC ACID CYCLE Glucose Pyruvate Krebs Mitochondrion Cytoplasm ATP CO2 CO2 ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation