9.3 Microbial Physiology Module 9: Metabolism

Which of the following coenzymes inhibit the enzymes of the citric acid cycle when they accumulate in excess?

• ATP and NADH

• ADP and NAD+

• FADH2 and NAD+

• none of these

Answer explanation

Answer: a. ATP and NADH. ATP and NADH inhibit key enzymes, signaling sufficient energy availability

Reference:

Brock et al., 2021

https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/variations-on-cellular-respiration/a/regulation-of-cellular-respiration

Which of the following correctly describes the electron flow in complex IV?

• cytochrome a → cytochrome b → cytochrome c

• cytochrome a → cytochrome a3 → cytochrome c

• cytochrome a3 → cytochrome a → cytochrome c

• cytochrome c → cytochrome a → cytochrome a3

Answer explanation

Answer: d. cytochrome c → cytochrome a → cytochrome a3. In complex IV, electrons flow from cytochrome c to cytochromes a and a₃, contributing to the reduction of oxygen

References:

Brock et al., 2021

Struck & White, 2019

Which of the following metabolic pathways involves the transport of electron and H+ ions and the subsequent synthesis of ATP molecules?

• the oxidative phosphorylation pathway

• the citric acid cycle

• the oxidative phosphorylation pathway and the citric acid cycle

• none of these

Answer explanation

Answer: a. the oxidative phosphorylation pathway. Oxidative phosphorylation generates ATP by transferring electrons through the electron transport chain

Reference:

Brock et al., 2021

What is the role of phosphofructokinase in glycolysis?

• It converts fructose into fructose 1-phosphate.

• It converts fructose 1-phosphate into fructose 1,6-bisphosphate.

• It converts fructose 1,6-bisphosphate into glucose 1,6-bisphosphate.

• None of these are correct.

Answer explanation

Answer: d. None of these are correct.

Rationale: Phosphofructokinase catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, not the options listed

Reference:

Struck & White, 2019

https://collab.its.virginia.edu/access/content/group/61ef6ea0-869d-476a-990a-9738e3899823/1/18__JoY__Phosphofructokinase-Geobacillus%20stearothermophilus__4PFK/18__JoY__Phosphofructokinase-Geobacillus%20stearothermophilus__4PFK_Reaction_Scheme.html

What is the main purpose of the Pentose Phosphate Pathway?

• ATP production

• Production of NADPH and ribose-5-phosphate

• Breakdown of fatty acids

• Synthesis of amino acids

Answer explanation

Answer: b. The PPP generates NADPH for biosynthetic reactions and ribose-5-phosphate for nucleotide synthesis

Reference:

Brock et al., 2021

To which of the following processes do the first five steps of glycolysis belong?

• the activation process

• the initiation process

• the initialization process

• the preparation process

Answer explanation

Answer: d. the preparation process. The first steps prime glucose for subsequent splitting and oxidation

Reference:

Brock et al., 2021

The conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate is a(n) _____ reaction.

• Hydrolysis

• Isomerization

• Oxidation

• Reduction

Answer explanation

Answer: c. oxidation. This step involves the oxidation of glyceraldehyde 3-phosphate, with NAD⁺ acting as the electron acceptor

Reference:
Bhagavan, N. (2002). Carbohydrate metabolism I: glycolysis and TCA cycle. In Elsevier eBooks (pp. 225–246). https://doi.org/10.1016/b978-012095440-7/50015-9

Struck & White, 2019

What is the by-product of the reaction that is involved in the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate?

• AMP

• ADP

• ATP

• None of these

Answer explanation

Answer: c. ATP. The conversion generates ATP via substrate-level phosphorylation

References:

Alfarouk, K. O., Verduzco, D., Rauch, C., Muddathir, A. K., Bashir, A. H. H., Elhassan, G. O., Ibrahim, M. E., Orozco, J. D. P., Cardone, R. A., Reshkin, S. J., & Harguindey, S. (2014). Glycolysis, tumor metabolism, cancer growth and dissemination. A new pH-based etiopathogenic perspective and therapeutic approach to an old cancer question. Oncoscience, 1(12), 777–802. https://doi.org/10.18632/oncoscience.109

Brock et al., 2021

Which cofactor is essential for enzymes in the glyoxylate cycle?

• NAD+

• FAD

• Mg²⁺

• ATP

Answer explanation

Cofactors like Mg²⁺ are essential for key enzymes in the glyoxylate cycle, such as isocitrate lyase and malate synthase. These metal ions help stabilize enzyme structures and facilitate crucial reactions, ensuring efficient metabolic function.

References:

Hans, S., Fatima, Z., & Hameed, S. (2019). Magnesium deprivation affects cellular circuitry involved in drug resistance and virulence in Candida albicans. Journal of Global Antimicrobial Resistance, 17, 263–275. https://doi.org/10.1016/j.jgar.2019.01.011

https://proteopedia.org/wiki/index.php/Glyoxylate_cycle

Which enzyme is involved in the conversion of phosphoenolpyruvate to pyruvate?

• Enolase

• Ketolase

• Pyruvate Kinase

• Pyruvate Oxidase

Answer explanation

Answer: c. pyruvate kinase. Pyruvate kinase catalyzes the final step of glycolysis

References:

Brock et al., 2021

Koendjbiharie JG, van Kranenburg R, Kengen SWM. The PEP-pyruvate-oxaloacetate node: variation at the heart of metabolism. FEMS Microbiol Rev. 2021 May 5;45(3):fuaa061. doi: 10.1093/femsre/fuaa061. PMID: 33289792; PMCID: PMC8100219.

Struck & White, 2019

http://clfs690.alivetek.org/CLFS690/glycolglucojmol/pyruvatekinase