9.5 Microbial Physiology Module 9: Metabolism

Which phase of the Pentose Phosphate Pathway generates NADPH?

• Oxidative phase

• Non-oxidative phase

• Both phases

• Neither phase

Answer explanation

Answer: a. NADPH is produced during the oxidative phase from glucose-6-phosphate

References:

Brock et al., 2021

Struck & White, 2019

Which enzyme catalyzes the conversion of glucose-6-phosphate to 6-phosphogluconolactone?

• Glucose-6-phosphate dehydrogenase

• Phosphofructokinase

• Hexokinase

• Transaldolase

Answer explanation

Answer: a. This step initiates the oxidative phase of the PPP and generates NADPH

References:

Brock et al., 2021

Reyes, J.S., Fuentes-Lemus, E., Figueroa, J.D. et al. Implications of differential peroxyl radical-induced inactivation of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase for the pentose phosphate pathway. Sci Rep 12, 21191 (2022). https://doi.org/10.1038/s41598-022-25474-x

Which molecule is a key product of the non-oxidative phase of the PPP?

• Fructose-6-phosphate

• Glucose

• Pyruvate

• NADH

Answer explanation

Answer: a. The non-oxidative phase produces intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate for glycolysis

References:

Brock et al., 2021

Gupta, R., Gupta, N. (2021). Pentose Phosphate Pathway. In: Fundamentals of Bacterial Physiology and Metabolism. Springer, Singapore. https://doi.org/10.1007/978-981-16-0723-3_10

Struck & White, 2019

Which key intermediate is formed during the Entner-Doudoroff pathway?

• Glucose-6-phosphate

• 6-phosphogluconate

• Fructose-1,6-bisphosphate

• Succinyl-CoA

Answer explanation

Answer: b

Rationale: 6-phosphogluconate is an intermediate specific to the Entner-Doudoroff pathway

References:

Brock et al., 2021

Spector, M. (2009). Metabolism, central (Intermediary). In Elsevier eBooks (pp. 242–264). https://doi.org/10.1016/b978-012373944-5.00078-x

What is the main product of the Entner-Doudoroff pathway?

• Glucose

• 2 ATP

• NADPH and pyruvate

• Acetyl-CoA

Answer explanation

Answer: c

Rationale: This pathway generates pyruvate and NADPH, important for metabolism and biosynthesis

References:

Brock et al., 2021

Spector, M. (2009). Metabolism, central (Intermediary). In Elsevier eBooks (pp. 242–264). https://doi.org/10.1016/b978-012373944-5.00078-x

What is the primary function of the Methylglyoxal pathway?

• Degradation of glucose to CO₂

• Detoxification of methylglyoxal

• ATP production

• Lipid synthesis

Answer explanation

Answer: b. The pathway helps detoxify methylglyoxal, a toxic intermediate formed during glycolysis

References:

Kammerscheit X, Hecker A, Rouhier N, Chauvat F, Cassier-Chauvat C.2020.Methylglyoxal Detoxification Revisited: Role of Glutathione Transferase in Model Cyanobacterium Synechocystis sp. Strain PCC 6803. mBio11:10.1128/mbio.00882-20.https://doi.org/10.1128/mbio.00882-20

Struck & White, 2019

Which enzyme converts methylglyoxal to lactate?

• Lactate dehydrogenase

• Glyoxalases

•  Aldolase

• PEPCK

Answer explanation

Answer: d. The complete conversion of methylglyoxal to D-lactate involves a two-enzyme system: Glyoxalase I and Glyoxalase II. Glyoxalase I uses glutathione to convert methylglyoxal into S-D-lactoylglutathione, and then Glyoxalase II hydrolyzes this intermediate to D-lactate and regenerates the glutathione. Since both are required, and Glyoxalase I is the first and unique step, selecting either indicates knowledge of this system. Given the choices, Glyoxalase I is the initiator, but Glyoxalase II completes the process; however, the overall reaction must involve Glyoxalase enzymes.

References:

Brock et al., 2021

Kammerscheit, X., Hecker, A., Rouhier, N., Chauvat, F., & Cassier-Chauvat, C. (2020). Methylglyoxal Detoxification Revisited: Role of Glutathione Transferase in Model Cyanobacterium Synechocystis sp. Strain PCC 6803. mBio, 11(4). https://doi.org/10.1128/mbio.00882-20

Which of the following organisms commonly use the phosphoketolase pathway?

• Lactic acid bacteria

• Cyanobacteria

• Archaea

• Mammals

Answer explanation

Answer: a. Lactic acid bacteria use the phosphoketolase pathway for sugar metabolism

References:

Spector, M. (2009). Metabolism, central (Intermediary). In Elsevier eBooks (pp. 242–264). https://doi.org/10.1016/b978-012373944-5.00078-x

Struck & White, 2019

Which is NOT a product generated by the phosphoketolase pathway?

• Pyruvate

• CO₂

• Acetate

• Ethanol

Answer explanation

Answer: a. The pathway produces acetate, lactate, and ethanol depending on the conditions

References:

Brock et al., 2021

Spector, M. (2009). Metabolism, central (Intermediary). In Elsevier eBooks (pp. 242–264). https://doi.org/10.1016/b978-012373944-5.00078-x

What is the purpose of the glyoxylate cycle?

• Energy production from glucose

• Conversion of fats to carbohydrates

• ATP synthesis

• Protein degradation

Answer explanation

Answer: b. The glyoxylate cycle allows cells to convert fatty acids into carbohydrates for growth

Reference:

Brock et al., 2021