Part 2 — Glycolysis (25 MCQs)

Part 2 — Glycolysis (25 MCQs)

1. Where does glycolysis occur in plant cells?
   A. Mitochondrial matrix
   B. Cytosol (cytoplasm)
   C. Chloroplast stroma
   D. Vacuole
   Answer: B. Cytosol (cytoplasm)
   Explanation:

• A: Mitochondrial matrix hosts TCA and oxidative phosphorylation, not glycolysis.

• B (Correct): Glycolysis is a cytosolic pathway in eukaryotes.

• C: Chloroplast stroma contains Calvin cycle and photosynthetic reactions.

• D: Vacuole is storage, not glycolytic site.

2. Net ATP produced per glucose molecule by glycolysis (substrate-level phosphorylation) is:
   A. 4 ATP
   B. 2 ATP
   C. 36 ATP
   D. 0 ATP
   Answer: B. 2 ATP
   Explanation:

• A: Glycolysis produces 4 ATP gross, but 2 are used in early steps → net 2 ATP.

• B (Correct): Net gain is 2 ATP.

• C: 36 ATP is overall respiration estimate, not glycolysis-only.

• D: Incorrect — glycolysis yields net ATP.

3. Which enzyme catalyzes the phosphorylation of glucose to glucose-6-phosphate in glycolysis?
   A. Hexokinase
   B. Phosphofructokinase (PFK)
   C. Pyruvate kinase
   D. Aldolase
   Answer: A. Hexokinase
   Explanation:

• A (Correct): Hexokinase phosphorylates glucose to G6P using ATP.

• B: PFK acts later on fructose-6-phosphate.

• C: Pyruvate kinase catalyzes final step producing pyruvate and ATP.

• D: Aldolase splits fructose-1,6-bisphosphate into triose phosphates.

4. Which step in glycolysis is the major regulatory/committed step?
   A. Glucose → G6P by hexokinase
   B. F6P → F1,6BP by phosphofructokinase-1 (PFK-1)
   C. PEP → Pyruvate by pyruvate kinase
   D. G3P → 1,3-BPG by glyceraldehyde-3-phosphate dehydrogenase
   Answer: B. F6P → F1,6BP by PFK-1
   Explanation:

• A: Hexokinase is important but PFK is the major rate-limiting/committed step.

• B (Correct): PFK is allosterically regulated and commits F6P to glycolysis.

• C: Pyruvate kinase is regulatory but not the main committed step.

• D: This step produces NADH but is not the committed step.

5. How many NADH molecules are generated per glucose during glycolysis?
   A. 0
   B. 1
   C. 2
   D. 4
   Answer: C. 2
   Explanation:

• A/B: Incorrect; glyceraldehyde-3-phosphate dehydrogenase produces NADH for each of two triose phosphates.

• C (Correct): Two molecules of NADH (one per glyceraldehyde-3-phosphate → 1,3-BPG).

• D: Not correct.

6. Which glycolytic enzyme catalyzes the irreversible conversion of phosphoenolpyruvate (PEP) to pyruvate?
   A. Enolase
   B. Pyruvate kinase
   C. Phosphoglycerate kinase
   D. Triose phosphate isomerase
   Answer: B. Pyruvate kinase
   Explanation:

• A: Enolase converts 2-phosphoglycerate to PEP.

• B (Correct): Pyruvate kinase catalyzes PEP → pyruvate and produces ATP.

• C: Phosphoglycerate kinase catalyzes 1,3-BPG → 3-phosphoglycerate (ATP generation).

• D: Triose phosphate isomerase interconverts DHAP and G3P.

7. Which of the following is produced by glycolysis and can be further converted into ethanol in anaerobic fermentation?
   A. Oxaloacetate
   B. Pyruvate
   C. Acetyl-CoA
   D. Citrate
   Answer: B. Pyruvate
   Explanation:

• A: Oxaloacetate is a TCA intermediate.

• B (Correct): Pyruvate is produced by glycolysis and is the substrate for fermentation to ethanol or lactate.

• C: Acetyl-CoA arises from pyruvate via PDH under aerobic conditions.

• D: Citrate is a TCA intermediate.

8. In glycolysis, which intermediate is the first to have a high-energy phosphate bond used to generate ATP?
   A. Fructose-1,6-bisphosphate
   B. 1,3-Bisphosphoglycerate (1,3-BPG)
   C. 3-Phosphoglycerate
   D. Glucose-6-phosphate
   Answer: B. 1,3-Bisphosphoglycerate (1,3-BPG)
   Explanation:

• A: Fructose-1,6-bisphosphate does not directly donate phosphate to ADP.

• B (Correct): 1,3-BPG donates a phosphate to ADP via phosphoglycerate kinase producing ATP.

• C: 3-PG is after ATP generation.

• D: G6P has phosphate attached, not a high-energy phosphate donor.

9. Which coenzyme is reduced during the glyceraldehyde-3-phosphate dehydrogenase step?
   A. FAD
   B. NAD⁺
   C. NADP⁺
   D. CoA
   Answer: B. NAD⁺
   Explanation:

• A: FAD is not involved in glycolytic oxidation.

• B (Correct): NAD⁺ accepts electrons to become NADH in this step.

• C: NADP⁺ is primarily used in anabolic (biosynthetic) reactions (e.g., photosynthesis).

• D: CoA accepts acyl groups, not used here.

10. Which glycolytic enzyme interconverts dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P)?
    A. Aldolase
    B. Triose phosphate isomerase (TPI)
    C. Phosphoglycerate mutase
    D. Hexokinase
    Answer: B. Triose phosphate isomerase (TPI)
    Explanation:

• A: Aldolase cleaves F1,6BP into DHAP and G3P.

• B (Correct): TPI rapidly interconverts DHAP and G3P; only G3P continues in glycolysis.

• C/D: Not involved in that interconversion.

11. Which statement about glycolysis is TRUE?
    A. It requires oxygen.
    B. It occurs only in heterotrophs.
    C. It yields pyruvate which can be used aerobically or anaerobically.
    D. It produces FADH₂ directly.
    Answer: C. It yields pyruvate which can be used aerobically or anaerobically.
    Explanation:

• A: Glycolysis is anaerobic (doesn’t require oxygen).

• B: Occurs in almost all organisms (autotrophs & heterotrophs).

• C (Correct): Pyruvate produced can be converted to acetyl-CoA aerobically or to lactate/ethanol anaerobically.

• D: Glycolysis produces NADH, not FADH₂.

12. Which of the following glycolytic enzymes produces ATP by substrate-level phosphorylation?
    A. Glyceraldehyde-3-phosphate dehydrogenase
    B. Phosphoglycerate kinase and pyruvate kinase
    C. Hexokinase only
    D. Enolase only
    Answer: B. Phosphoglycerate kinase and pyruvate kinase
    Explanation:

• A: This enzyme produces NADH and 1,3-BPG but not ATP directly.

• B (Correct): Phosphoglycerate kinase (1,3-BPG → 3-PG) and pyruvate kinase (PEP → pyruvate) generate ATP.

• C/D: Incorrect.

13. Which of the following would increase the rate of glycolysis?
    A. High ATP concentration
    B. High citrate concentration
    C. High AMP/ADP concentration
    D. High NADH concentration
    Answer: C. High AMP/ADP concentration
    Explanation:

• A: High ATP inhibits glycolysis (feedback inhibition).

• B: Citrate is an inhibitor (signals sufficient TCA intermediates).

• C (Correct): High AMP/ADP indicate low energy charge → stimulate PFK and glycolysis.

• D: High NADH suggests reduced conditions and can inhibit some steps.

14. Which intermediate of glycolysis can be diverted into the pentose phosphate pathway?
    A. 3-Phosphoglycerate
    B. Fructose-6-phosphate and glucose-6-phosphate
    C. Phosphoenolpyruvate
    D. Pyruvate
    Answer: B. Fructose-6-phosphate and glucose-6-phosphate
    Explanation:

• A: 3-PG is later; not a PPP entry.

• B (Correct): G6P is the main entry for the oxidative branch of the pentose phosphate pathway; F6P can also interconvert in non-oxidative branch.

• C/D: Not direct entries.

15. Which of the following is an irreversible step in glycolysis?
    A. Glyceraldehyde-3-phosphate → 1,3-BPG
    B. Fructose-6-phosphate → Fructose-1,6-bisphosphate
    C. 3-Phosphoglycerate → 2-Phosphoglycerate
    D. 2-Phosphoglycerate → PEP
    Answer: B. F6P → F1,6BP
    Explanation:

• A: This step is reversible under cellular conditions.

• B (Correct): Catalyzed by PFK, irreversible and highly regulated.

• C/D: These are reversible steps.

16. Which enzyme is inhibited by high levels of ATP and citrate (feedback inhibition)?
    A. Hexokinase
    B. Phosphofructokinase (PFK)
    C. Aldolase
    D. Pyruvate dehydrogenase
    Answer: B. Phosphofructokinase (PFK)
    Explanation:

• A: Hexokinase has regulation but PFK is major metabolic control point.

• B (Correct): PFK is allosterically inhibited by ATP and citrate, signalling energy sufficiency.

• C: Not main regulatory enzyme for glycolysis.

• D: PDH is regulated but not inhibited by citrate directly (it’s inhibited by high NADH/ATP).

17. Which glycolytic intermediate is a direct 3-carbon product after aldolase cleavage?
    A. Glucose-6-phosphate
    B. Dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P)
    C. Phosphoenolpyruvate
    D. Fructose-6-phosphate
    Answer: B. DHAP and G3P
    Explanation:

• A/D: Six-carbon intermediates.

• B (Correct): Aldolase splits F1,6BP into these two 3-carbon molecules.

• C: PEP is 3-carbon but produced later.

18. Which compound is the substrate for glyceraldehyde-3-phosphate dehydrogenase?
    A. Glyceraldehyde-3-phosphate (G3P)
    B. Dihydroxyacetone phosphate (DHAP)
    C. 3-Phosphoglycerate
    D. Fructose-1,6-bisphosphate
    Answer: A. Glyceraldehyde-3-phosphate (G3P)
    Explanation:

• A (Correct): G3P is oxidized to 1,3-BPG with reduction of NAD⁺ to NADH.

• B: DHAP must be isomerized to G3P to be substrate.

• C/D: Not substrates for this dehydrogenase.

19. Which of the following is TRUE about the energy investment phase of glycolysis?
    A. ATP is generated during this phase.
    B. Two ATP molecules are consumed per glucose.
    C. NADH is produced in this phase.
    D. Pyruvate is formed in this phase.
    Answer: B. Two ATP molecules are consumed per glucose.
    Explanation:

• A: ATP is consumed, not generated.

• B (Correct): ATP used by hexokinase and PFK (one each) — total 2.

• C: NADH is produced later in payoff phase.

• D: Pyruvate formed in payoff phase.

20. Which glycolytic enzyme requires inorganic phosphate (Pi) and NAD⁺ to form a high-energy intermediate?
    A. Hexokinase
    B. Glyceraldehyde-3-phosphate dehydrogenase
    C. Phosphoglycerate kinase
    D. Aldolase
    Answer: B. Glyceraldehyde-3-phosphate dehydrogenase
    Explanation:

• A/C/D: These don’t directly require Pi + NAD⁺ to form 1,3-BPG.

• B (Correct): This enzyme oxidizes G3P while adding inorganic phosphate to form 1,3-BPG and reduce NAD⁺ to NADH.

21. Which statement is correct about glycolysis in plants?
    A. It is linked with photosynthesis and can operate in the light.
    B. It only functions in dark-grown tissues.
    C. It cannot run in non-photosynthetic tissues.
    D. It is exclusively present in heterotrophic organisms.
    Answer: A. It is linked with photosynthesis and can operate in the light.
    Explanation:

• A (Correct): Glycolysis runs in photosynthetic tissues even in light to provide intermediates and energy.

• B/C/D: Incorrect; glycolysis occurs broadly in plant tissues regardless of light (with regulatory cross-talk).

22. Which product of glycolysis is important for biosynthetic pathways (lipid, amino acid biosynthesis)?
    A. Pyruvate only
    B. 3-Phosphoglycerate and pyruvate (multiple intermediates)
    C. Fructose-1,6-bisphosphate only
    D. No glycolytic intermediate is used biosynthetically
    Answer: B. 3-Phosphoglycerate and pyruvate (multiple intermediates)
    Explanation:

• A: Pyruvate is used but other intermediates like 3-PG serve as precursors for amino acids (serine) and lipids via acetyl-CoA.

• B (Correct): Multiple glycolytic intermediates provide carbon skeletons for biosynthesis.

• C/D: Incorrect.

23. Which glycolytic enzyme is activated by fructose-1,6-bisphosphate (feed-forward activation)?
    A. Hexokinase
    B. Pyruvate kinase
    C. Phosphofructokinase
    D. Aldolase
    Answer: B. Pyruvate kinase
    Explanation:

• A: Not primarily.

• B (Correct): Fructose-1,6-bisphosphate activates pyruvate kinase (feed-forward), promoting glycolysis.

• C: PFK is regulated but not activated by F1,6BP (it’s upstream).

• D: Aldolase is not the main regulated enzyme.

24. Which statement correctly describes the fate of cytosolic NADH made in glycolysis in aerobic plant cells?
    A. It is used directly in mitochondrial oxidative phosphorylation.
    B. It is always oxidized in cytosol to NAD⁺ and not used.
    C. Shuttle systems transfer electrons to mitochondrial carriers.
    D. It becomes NADPH for biosynthesis.
    Answer: C. Shuttle systems transfer electrons to mitochondrial carriers.
    Explanation:

• A: NADH cannot cross the inner mitochondrial membrane directly.

• B: Some cytosolic NADH may be oxidized in cytosol but under aerobic conditions shuttles transfer reducing equivalents.

• C (Correct): Shuttle systems (e.g., malate-aspartate or glycerol-3-phosphate) move electrons into mitochondria.

• D: NADH is not directly converted to NADPH in this context.

25. Which triose phosphate is directly used to form glycerol backbone during lipid synthesis?
    A. 3-Phosphoglycerate
    B. Glyceraldehyde-3-phosphate (via DHAP)
    C. Pyruvate
    D. Phosphoenolpyruvate
    Answer: B. Glyceraldehyde-3-phosphate (via DHAP)
    Explanation:

• A/C/D: Not direct glycerol precursors.

• B (Correct): DHAP can be reduced to glycerol-3-phosphate, the backbone for triglyceride synthesis.

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