BiochemistryLesson 2 of 2 in the course How Cells Obtain Energy

Fermentation and Anaerobic Respiration: NAD⁺ Recycling and Pathway Differences

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

When oxygen is unavailable, cells still need a way to keep glycolysis running. This lesson explains how fermentation regenerates NAD⁺, how lactic acid and alcohol fermentation differ, and how anaerobic respiration uses other electron acceptors.

During aerobic respiration, oxygen is the final electron acceptor in the electron transport chain (ETC). NADH and FADH₂ deliver high-energy electrons to the ETC, and the energy released helps produce ATP.

All flashcards

What is the central role of fermentation?
Fermentation transfers electrons from NADH to an organic molecule, regenerating NAD⁺ so glycolysis can continue when aerobic respiration is unavailable. Fermentation itself does not use an ETC.
What are the products and key enzyme of lactic acid fermentation?
Pyruvic acid is converted to lactic acid as NADH is oxidized to NAD⁺. Lactate dehydrogenase catalyzes the reaction.
How does alcohol fermentation produce ethanol?
Pyruvic acid first loses carbon dioxide to form acetaldehyde. Acetaldehyde then accepts electrons from NADH and becomes ethanol, regenerating NAD⁺.
How does anaerobic respiration differ from fermentation?
Anaerobic respiration uses an electron transport chain with an inorganic final electron acceptor other than oxygen. Fermentation does not use an ETC and transfers electrons to an organic molecule.
What distinguishes facultative anaerobes from obligate anaerobes?
Facultative anaerobes can switch between aerobic respiration and fermentation depending on oxygen availability. Obligate anaerobes live without molecular oxygen, which can be toxic to them.

Quiz questions

  1. Why must cells regenerate NAD⁺ when aerobic respiration is unavailable?Answer: Glycolysis requires NAD⁺ to accept electrons, so regenerating it allows glycolysis to continue.
  2. What accepts electrons from NADH during fermentation?Answer: An organic molecule, such as pyruvate or a molecule derived from it.
  3. Which statement correctly describes lactic acid fermentation in muscle?Answer: It converts pyruvic acid to lactic acid, regenerates NAD⁺, and usually produces no gas.
  4. What happens during alcohol fermentation after pyruvic acid loses carbon dioxide?Answer: Acetaldehyde accepts electrons from NADH and becomes ethanol, regenerating NAD⁺.
  5. A microorganism uses an ETC with sulfate as its final electron acceptor. How is this pathway classified?Answer: Anaerobic cellular respiration, using an ETC and an inorganic acceptor other than oxygen.

Based on Concepts of Biology by Samantha Fowler, Rebecca Roush, James Wise (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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