Q.90 The end products of glycolysis include ATP,
(A) CO2 and H2O (B) H2O and pyruvate
(C) NADH and pyruvate (D) CO2 and NADH
Glycolysis stands as the foundational metabolic pathway in cellular respiration, breaking down glucose into energy-rich molecules without oxygen. For students tackling exams in molecular biology or biotechnology, understanding its glycolysis end products is crucial. This article dives into a common multiple-choice question (MCQ) on the topic, reveals the correct answer, and explains every option with clear science.
Correct Answer: (C) NADH and pyruvate
Glycolysis produces a net gain of 2 ATP, 2 NADH, and 2 pyruvate molecules from one glucose molecule. These form the primary glycolysis end products, fueling subsequent stages like the Krebs cycle or fermentation.
Detailed Explanation of Glycolysis
Glycolysis occurs in the cytoplasm and consists of 10 enzyme-catalyzed steps. It starts with glucose phosphorylation and ends with pyruvate formation. Key outputs include:
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2 ATP (net): From substrate-level phosphorylation (4 ATP produced minus 2 used).
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2 NADH: Reduced from NAD⁺ during glyceraldehyde-3-phosphate oxidation.
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2 Pyruvate: The final carbon skeletons.
No oxygen is required, making it anaerobic. The balanced equation is:
\ceGlucose+2NAD++2ADP+2Pi−>2Pyruvate+2NADH+2ATP+2H++2H2O
This confirms ATP, NADH, and pyruvate as the hallmarks of glycolysis end products.
Why Option (C) is Correct: NADH and Pyruvate
In the payoff phase, steps 6-10 generate:
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NADH via glyceraldehyde-3-phosphate dehydrogenase.
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Pyruvate via pyruvate kinase, which also yields ATP.
These molecules drive ATP production in aerobic (electron transport chain) or anaerobic (lactic acid fermentation) conditions. For bioinformatics enthusiasts, tools like KEGG pathways visualize this precisely.
Breakdown of Incorrect Options
Each wrong choice confuses glycolysis with later respiration stages. Here’s why they fail:
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(A) CO2 and H2O: These emerge in the Krebs cycle (CO₂ from decarboxylation) and electron transport chain (H₂O from oxygen reduction). Glycolysis produces zero CO₂ or H₂O as net end products—H₂O appears intermediately but cancels out.
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(B) H2O and pyruvate: Pyruvate is correct, but H₂O isn’t a net product. While water forms in enolase step, it’s consumed elsewhere, yielding no net H₂O. This mixes facts misleadingly.
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(D) CO2 and NADH: NADH is right, but CO₂ is absent. CO₂ release happens post-glycolysis in mitochondria, not here.
| Option | Includes ATP? | Correct Components | Why Wrong? |
|---|---|---|---|
| (A) CO2 and H2O | Yes | None | Products of Krebs/ETC, not glycolysis |
| (B) H2O and pyruvate | Yes | Pyruvate only | No net H2O |
| (C) NADH and pyruvate | Yes | Both | Matches exactly |
| (D) CO2 and NADH | Yes | NADH only | No CO2 |
Relevance for Students and Researchers
Mastering glycolysis end products aids in genetics, microbiology, and bioengineering. In cancer research, glycolytic shifts (Warburg effect) highlight pyruvate’s role. For exam prep, visualize via sequence alignments in bioinformatics tools like BLAST for enzyme genes.
This breakdown ensures you ace similar MCQs. Practice with diagrams for retention.
