EMQ 7. Theme: the locations where energy production occurs

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The following stages describe how glucose is released from its stored form, glycogen, and then processed to fuel cellular energy production. For each stage, identify from the list below the location of the enzymes responsible. If a stage involves multiple steps, state the location where the majority of the steps occur.

A Extracellular medium
B Non-organelle cytoplasm (cytosol plus structures within the cytoplasm, such as the cytoskeleton, that are not membrane-bound)
C Nucleus
D Peroxisome
E Lysosome
F Endoplasmic reticulum
G Outer mitochondrial membrane
H Mitochondrial intermembrane space
I Inner mitochondrial membrane
J Mitochondrial matrix

1. Individual glucose units are split from glycogen, becoming phosphorylated in the process.
Your Answer:
Answer: B, cytoplasm. The reaction occurs at the surface of glycogen granules in the cytoplasm. See book pages 26 and 212.
2. Glucose phosphate is broken down to pyruvate with the net production of three molecules of ATP.
Your Answer:
Answer: B, cytoplasm. The reactions of glycolysis occur in the cytosol. See book page 209. Note that because the question stated that we began with glucose phosphate, the net ATP gain is three (see figure 13.3 on book page 210).
3. Pyruvate is decarboxylated and joined to coenzyme A to generate acetyl CoA. At the same time NAD+ is reduced to NADH.
Your Answer:
Answer: J, the mitochondrial matrix. The reaction is carried out by the complex enzyme pyruvate dehydrogenase. See book page 210.
4.Acetate bound to CoA is completely oxidized to carbon dioxide and water. NAD+ is reduced to NADH and FAD is reduced to FADH2
Your Answer:
Answer: J, the mitochondrial matrix. This is the Krebs cycle (book page 208). One of the steps, catalyzed by succinate dehydrogenase, takes place on the inner mitochondrial membrane, but all the others take place in the aqueous matrix.
5. NADH acts to reduce coenzyme Q, beoming oxidized to NAD+ in the process.
Your Answer:
Answer: I, the inner mitochondrial membrane. This is the first step in the electron transport chain and is carried out by complex I. See book page 196.
6. Reduced coenzyme Q acts to reduce cytochrome c, becoming oxidized in the process.
Your Answer:
Answer: I, the inner mitochondrial membrane. This step in the electron transport chain is carried out by complex III. See book page 197.
7. Reduced cytochrome c acts to reduce molecular oxygen, becoming oxidized in the process.
Your Answer:
Answer: I, the inner mitochondrial membrane. This step in the electron transport chain is carried out by complex IV. See book page 197.
8. Hydrogen peroxide, a byproduct formed every so often by the electron transport chain, is safely converted to water and molecular oxygen.
Your Answer:
Answer: D, the peroxisome. See book page 49.
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