- When yeast produce ethanol from glucose, the reaction of acetaldehyde to form ethanol directly
(1) generates ATP
(2) produces NADH
(3) regenerates NAD+
(4) contributes to the proton motive force
Yeast cells ferment glucose to ethanol through a well-coordinated metabolic pathway that allows them to generate energy in the absence of oxygen. One critical step in this process is the conversion of acetaldehyde to ethanol. This reaction is catalyzed by the enzyme alcohol dehydrogenase and plays a vital role in maintaining the redox balance within the cell.
This article explains the biochemical significance of the acetaldehyde-to-ethanol conversion in yeast fermentation, focusing on how it regenerates NAD+ to sustain glycolysis and ATP production.
The Fermentation Pathway in Yeast
Yeast metabolizes glucose through glycolysis, producing pyruvate, ATP, and NADH. Under anaerobic conditions, pyruvate is decarboxylated to acetaldehyde by pyruvate decarboxylase, releasing CO2. The next step involves reducing acetaldehyde to ethanol.
The overall simplified reaction for this step is:
Acetaldehyde+NADH+H+→Ethanol+NAD+
Why Is This Reaction Important?
Regeneration of NAD+
During glycolysis, NAD+ is reduced to NADH as glucose is broken down to pyruvate. For glycolysis to continue, NAD+ must be regenerated. In aerobic cells, NADH donates electrons to the mitochondrial electron transport chain, regenerating NAD+. However, yeast cells fermenting glucose anaerobically lack this option.
The reduction of acetaldehyde to ethanol regenerates NAD+ from NADH, allowing glycolysis to proceed continuously and produce ATP via substrate-level phosphorylation.
ATP Production
While the acetaldehyde to ethanol step itself does not produce ATP directly, it is crucial for sustaining glycolysis, which generates ATP. Without NAD+ regeneration, glycolysis would halt, and the cell would be unable to meet its energy demands.
No Contribution to Proton Motive Force
This reaction does not contribute to the proton motive force or oxidative phosphorylation, as fermentation is an anaerobic process that bypasses the electron transport chain.
Evaluating the Given Options
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Generates ATP
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Incorrect. The acetaldehyde to ethanol reaction does not directly generate ATP.
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Produces NADH
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Incorrect. This reaction consumes NADH, converting it back to NAD+.
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Regenerates NAD+
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Correct. The key role of this reaction is to regenerate NAD+ to keep glycolysis running.
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Contributes to the proton motive force
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Incorrect. Fermentation does not involve the electron transport chain or proton motive force generation.
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Conclusion
The conversion of acetaldehyde to ethanol in yeast fermentation is essential for regenerating NAD+, which sustains glycolysis and ATP production under anaerobic conditions. This reaction maintains cellular energy balance when oxygen is absent.
Correct answer: (3) regenerates NAD+
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31 Comments
Kirti Agarwal
September 18, 2025Regenrates NAD+
Aakansha sharma Sharma
September 19, 2025Regenrates NAD+
Neha Yadav
September 20, 2025Acetaldehyde to ethanol in fermantation regenerate NAD +
Bhawna Choudhary
September 20, 2025Regenerate NAD+
Khushi Agarwal
September 21, 2025Correct answer: (3)
regenerates NAD+
Soniya Shekhawat
September 21, 2025Acetaldehyde to ethanol in fermentation regenerate NAD + , not produced NADH,ATP , not causing proton motive force.
Sonal Nagar
September 21, 2025regenerates NAD+
Manisha choudhary
September 21, 2025Yeast m anaerobic glycolysis hota h
Glycolysis ko continue rkhne k liye NAD+ regenerate Krna hota h
Yeast k paas mitrochondria nhi hoti , NADH apne electrone and H+ ion mitrochondria ko dete h and NAD+ m convert ho jate h
Yeast m glycolysis ko continue rkhnek liye pyruvate ko decarboxylase enzyme dwara acetaldehyde m convert Kiya jata h then acetaldehyde ko dehydrogenase enzyme dwara ethanol m convert Kiya jata h jaha gluconeogenesis k doran 3PGL s 1,3BPGA bnate time jo NADH form hota h use use kr k NADH ko NAD+ m convert Kiya jata h
Minal Sethi
September 22, 2025regenerates NAD+
Pallavi Ghangas
September 22, 2025regenerates NAD+
Heena Mahlawat
September 23, 2025Produces nad+
Roopal Sharma
September 23, 2025Regenerate nad+
Aafreen Khan
September 23, 2025Correct answer is – Regenerates NAD+ This regeneration is essential for maintaining glycolysis in anaerobic conditions
Dharmpal Swami
September 23, 2025Glucose to alcohal by yeast regenerate NAD+
Deepika sheoran
September 23, 2025Option 3rd
Regenerate NAD+
Anurag Giri
September 23, 2025The conversion of acetaldehyde to ethanol in yeast fermentation is essential for regenerating NAD+
Devika
September 24, 2025Regenerates NAD+
Nilofar Khan
September 24, 2025Regenerating NAD+
Deepika sheoran
September 24, 2025Regenerate NAD+
Mohd juber Ali
September 24, 2025Acetaldehyde to ethenol
NADH➡️NAD+ mean regenerate NAD+
Payal Gaur
September 25, 2025Regenrate NAD+
Divya rani
September 25, 2025Yeast produce alcohol from glucose in the adsence of oxygen with a very well co ordinated Metabolic pathway, in this reaction acetaldehyde Convert into alcohol with regenerated NAD+.
Santosh Saini
September 25, 2025Acetaldehyde convert into ethanol with regenerating NAD+
Kavita Choudhary
September 25, 2025Acetaldehyde convert into ethonl and NADH convert NAD mens regenerate NAD+
sakshi vijay
September 25, 2025this rxn generate nad+ to continue glycolysis and atp production under anaerobic condition
Avni
September 25, 2025The key role of this reaction is to regenerate NAD+ to keep glycolysis running
Muskan Yadav
September 26, 2025regenerates NAD+ .
Arushi Saini
September 27, 2025Regenrates NAD+
karishma don
October 1, 2025Correct answer: (3) regenerates NAD+
Kajal
October 3, 2025Regeneration of NAD+
Sakshi Kanwar
November 25, 2025regenerate NAD+ to keep glycolysis running