Use the following choices to answer the question.a. E. coli growing in glucose broth at 35℃ with O2 for 5 daysb. E. coli growing in glucose broth at 35℃ without O2 for 5 daysc. Both a and bd. Neither a nor bWhich culture uses NAD+ ?

Ch. 5 - Microbial Metabolism

Tortora - Microbiology: An Introduction 14th Edition

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Ch. 5 - Microbial Metabolism

Problem 9

Chapter 5, Problem 9

Use the following choices to answer the question.
a. E. coli growing in glucose broth at 35℃ with O₂ for 5 days
b. E. coli growing in glucose broth at 35℃ without O₂ for 5 days
c. Both a and b
d. Neither a nor b

Which culture uses NAD⁺ ?

Verified step by step guidance

Step 1: Understand the role of NAD⁺ in cellular metabolism. NAD⁺ (nicotinamide adenine dinucleotide) is a coenzyme that acts as an electron acceptor in redox reactions, especially during glycolysis and cellular respiration.

Step 2: Identify the metabolic pathways used by E. coli under different oxygen conditions. When oxygen is present (aerobic conditions), E. coli performs aerobic respiration, where NAD⁺ is reduced to NADH during glycolysis and the Krebs cycle.

Step 3: Consider the anaerobic condition (without O₂). In the absence of oxygen, E. coli switches to fermentation or anaerobic respiration, which also requires NAD⁺ to accept electrons during glycolysis to keep the pathway running.

Step 4: Analyze the options: both aerobic (a) and anaerobic (b) growth require NAD⁺ to accept electrons during glycolysis, so both cultures use NAD⁺.

Step 5: Conclude that the correct choice is the one indicating that both cultures use NAD⁺, because NAD⁺ is essential for energy metabolism regardless of oxygen presence.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Role of NAD⁺ in Cellular Metabolism

NAD⁺ (nicotinamide adenine dinucleotide) is a crucial coenzyme that acts as an electron carrier in metabolic reactions. It accepts electrons during the breakdown of glucose, becoming NADH, which then transfers electrons to the electron transport chain or other pathways to regenerate NAD⁺. This regeneration is essential for continuous glycolysis and energy production.

Aerobic vs. Anaerobic Respiration in E. coli

E. coli can grow in both the presence and absence of oxygen. Under aerobic conditions, NADH donates electrons to oxygen via the electron transport chain, regenerating NAD⁺ efficiently. Under anaerobic conditions, E. coli uses fermentation or anaerobic respiration to regenerate NAD⁺, allowing glycolysis to continue despite the lack of oxygen.

Glucose Metabolism and NAD⁺ Utilization

During glucose metabolism, NAD⁺ is reduced to NADH in glycolysis and the Krebs cycle. For metabolism to continue, NADH must be oxidized back to NAD⁺. Both aerobic and anaerobic growth conditions require NAD⁺ to accept electrons, but the mechanisms of NAD⁺ regeneration differ depending on oxygen availability.

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What nutritional type is a colorless microbe that uses the Calvin-Benson cycle, uses H₂ as the electron donor to its ETC, and uses elemental S as the final electron acceptor in the ETC?

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Textbook Question

Why must NADH be reoxidized? How does this happen in an organism that uses respiration? Fermentation?

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Textbook Question

Write your own definition of the chemiosmotic mechanism of ATP generation. On Figure 5.16, mark the following using the appropriate letter:

a. The acidic side of the membrane

b. The side with a positive electrical charge

c. Potential energy

d. Kinetic energy