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Glycolysis

Tier 1 · #9 of 33 · highest yield · topic 3.5 — every high-yield fact from the book chapter, exam-ready.

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  1. Front
    In which subcellular compartment does glycolysis occur?
    Back
    The cytosol
  2. Front
    What is the net per-glucose yield of glycolysis (ATP, NADH, and end product)?
    Back
    2 ATP , 2 NADH , and 2 pyruvate
  3. Front
    The three irreversible (and regulated) steps of glycolysis are catalyzed by hexokinase/glucokinase , ______, and pyruvate kinase .
    Back
    PFK-1 ( phosphofructokinase-1 )
  4. Front
    Which enzyme is the rate-limiting (committed) step of glycolysis ?
    Back
    PFK-1 ( phosphofructokinase-1 )
  5. Front
    Why does phosphorylating glucose to glucose-6-phosphate trap it inside the cell?
    Back
    G6P is not a substrate for the glucose transporters , so it cannot cross the plasma membrane
  6. Front
    What is the approximate Km for glucose of hexokinase I (low-Km tissue isoform)?
    Back
    ~0.05 mM
  7. Front
    What is the approximate Km for glucose of glucokinase ( hexokinase IV )?
    Back
    ~5–10 mM
  8. Front
    Which hexokinase isoform is inhibited by its own product , G6P ?
    Back
    Hexokinases I–III (the low-Km tissue isoforms)
  9. Front
    In which two cell types is glucokinase ( hexokinase IV ) found?
    Back
    Hepatocytes and the beta cells of the pancreatic islets of Langerhans
  10. Front
    Why does glucokinase function as a glucose sensor rather than a constitutive scavenger?
    Back
    Its high Km (~5–10 mM) is above fasting blood glucose, so it only becomes fully active when glucose rises after a meal
  11. Front
    Glucokinase synthesis in the liver is dependent on which hormone?
    Back
    Insulin
  12. Front
    In the fasting state, what sequesters glucokinase in the hepatocyte nucleus ?
    Back
    Glucokinase regulatory protein (GKRP)
  13. Front
    Which enzyme converts glucose-6-phosphate to fructose-6-phosphate (step 2)?
    Back
    Phosphoglucose isomerase
  14. Front
    PFK-1 phosphorylates fructose-6-phosphate to which product?
    Back
    Fructose-1,6-bisphosphate (F1,6BP)
  15. Front
    Which enzyme physically splits fructose-1,6-bisphosphate into two three-carbon fragments?
    Back
    Aldolase
  16. Front
    Aldolase cleaves F1,6BP into which two three-carbon molecules?
    Back
    Dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P)
  17. Front
    Which enzyme converts DHAP to G3P so both fragments can enter the energy generation phase (step 5)?
    Back
    Triose phosphate isomerase
  18. Front
    Which glycolytic enzyme oxidizes G3P and reduces NAD+ to NADH (step 6)?
    Back
    Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)
  19. Front
    GAPDH oxidizes G3P and adds inorganic phosphate to form which high-energy intermediate?
    Back
    1,3-bisphosphoglycerate (1,3-BPG)
  20. Front
    If NAD+ is exhausted, which glycolytic enzyme stalls and halts the entire pathway ?
    Back
    GAPDH ( glyceraldehyde-3-phosphate dehydrogenase , step 6)
  21. Front
    The two substrate-level phosphorylation steps of glycolysis are catalyzed by which two enzymes?
    Back
    Phosphoglycerate kinase (step 7) and pyruvate kinase (step 10)
  22. Front
    What defines substrate-level phosphorylation (vs. oxidative phosphorylation)?
    Back
    Phosphate is transferred directly from a high-energy intermediate onto ADP — no electron transport chain or oxygen needed
  23. Front
    Phosphoglycerate kinase transfers phosphate from 1,3-BPG to ADP, forming ATP and which product (step 7)?
    Back
    3-phosphoglycerate (3-PG)
  24. Front
    Which enzyme dehydrates 2-phosphoglycerate to form phosphoenolpyruvate (step 9)?
    Back
    Enolase
  25. Front
    Which glycolytic enzyme is inhibited by fluoride ?
    Back
    Enolase (step 9)
  26. Front
    Why is sodium fluoride added to gray-top blood collection tubes for glucose measurement?
    Back
    It inhibits enolase , arresting glycolysis so red cells cannot consume glucose in the sample before it is measured
  27. Front
    Pyruvate kinase irreversibly transfers phosphate from PEP to ADP, forming ATP and which product (step 10)?
    Back
    Pyruvate
  28. Front
    PFK-1 is allosterically inhibited by which two molecules signaling high energy / a running Krebs cycle?
    Back
    ATP and citrate
  29. Front
    Besides AMP and ADP, what is the most potent allosteric activator of PFK-1 ?
    Back
    Fructose-2,6-bisphosphate (F2,6BP)
  30. Front
    Which bifunctional enzyme synthesizes and degrades fructose-2,6-bisphosphate ?
    Back
    PFK-2 / FBPase-2 (the bifunctional protein)
  31. Front
    Besides activating PFK-1 , what other effect does F2,6BP have on gluconeogenesis?
    Back
    It inhibits FBPase-1 , simultaneously accelerating glycolysis and braking gluconeogenesis
  32. Front
    In the fasting state, glucagon raises cAMP and activates PKA , which phosphorylates the PFK-2/FBPase-2 protein. What happens to F2,6BP and glycolysis?
    Back
    Phosphorylation inactivates PFK-2 and activates FBPase-2 , so F2,6BP falls and glycolysis slows
  33. Front
    Which hormone raises F2,6BP and accelerates hepatic glycolysis ?
    Back
    Insulin
  34. Front
    Pyruvate kinase is allosterically activated by which upstream glycolytic intermediate (feedforward activation)?
    Back
    Fructose-1,6-bisphosphate (F1,6BP)
  35. Front
    Pyruvate kinase is allosterically inhibited by ATP and which amino acid?
    Back
    Alanine
  36. Front
    Which isoform of pyruvate kinase undergoes covalent (PKA phosphorylation) regulation by glucagon ?
    Back
    The hepatic (L) isoform — the muscle M2 isoform is not regulated by phosphorylation
  37. Front
    Under anaerobic conditions, which enzyme reduces pyruvate to lactate to regenerate NAD+ ?
    Back
    Lactate dehydrogenase (LDH)
  38. Front
    What is the purpose of converting pyruvate to lactate in anaerobic glycolysis?
    Back
    It reoxidizes NADH back to NAD+ , allowing GAPDH to keep running so glycolysis continues
  39. Front
    What is the net ATP yield of anaerobic glycolysis per glucose?
    Back
    2 ATP ( glucose → 2 lactate + 2 ATP )
  40. Front
    The cycle in which muscle exports lactate , the liver reconverts it to glucose, and glucose returns to muscle is called the ______.
    Back
    Cori cycle
  41. Front
    Above what blood lactate concentration is the threshold for lactic acidosis ?
    Back
    5 mM
  42. Front
    Name two tissues that rely predominantly or entirely on anaerobic glycolysis.
    Back
    Erythrocytes (no mitochondria), renal medulla , lens of the eye , or skeletal muscle under intense exercise
  43. Front
    Under hypoxia, which transcription factor upregulates expression of glycolytic enzymes?
    Back
    HIF-1 ( hypoxia-inducible factor-1 )
  44. Front
    Which NADH shuttle (heart, liver, kidneys) yields ~2.5 ATP per cytosolic NADH?
    Back
    The malate-aspartate shuttle
  45. Front
    Which NADH shuttle delivers electrons to FADH2, yielding only ~1.5 ATP per NADH?
    Back
    The glycerol-3-phosphate shuttle
  46. Front
    What is the approximate total ATP yield from complete aerobic oxidation of one glucose?
    Back
    ~30–32 ATP
  47. Front
    2,3-bisphosphoglycerate (2,3-BPG) is made only in which cell type?
    Back
    Erythrocytes (red blood cells)
  48. Front
    How does 2,3-BPG affect hemoglobin's oxygen affinity?
    Back
    It binds deoxyhemoglobin and stabilizes the T-state , right-shifting the O2-dissociation curve to enhance O2 delivery to tissues
  49. Front
    Why must a separate enzyme ( pyruvate carboxylase ) bypass the pyruvate kinase step in gluconeogenesis?
    Back
    The pyruvate kinase reaction is strongly exergonic and essentially irreversible under cellular conditions
  50. Front
    Why does a type 1 diabetic (no insulin ) fail to trap glucose efficiently in the liver after a meal?
    Back
    Without insulin , glucokinase expression drops and F2,6BP falls, so the liver switches to gluconeogenesis even postprandially
  51. Front
    Which glycolytic enzyme shifts the phosphate from the 3-position to the 2-position, converting 3-phosphoglycerate to 2-phosphoglycerate (step 8)?
    Back
    Phosphoglycerate mutase
  52. Front
    Phosphoglycerate mutase converts 3-phosphoglycerate to which product?
    Back
    2-phosphoglycerate (2-PG)
  53. Front
    Which ordered enzyme sequence connects step 7 to step 9: 3-PG → 2-PG → PEP ?
    Back
    Phosphoglycerate mutase ( 3-PG → 2-PG ), then enolase ( 2-PG → PEP )
  54. Front
    List four causes of lactic acidosis taught in the chapter (all block aerobic NADH reoxidation).
    Back
    Hypoxia , CO poisoning , large amounts of alcohol , and strenuous exercise (plus defects in respiratory-chain or Krebs-cycle enzymes)
  55. Front
    How does hypoxia , CO poisoning , alcohol , or a respiratory-chain enzyme defect each cause lactate to accumulate?
    Back
    All block aerobic reoxidation of NADH , depleting NAD+ ; LDH must reduce pyruvate to lactate to regenerate NAD+
  56. Front
    Which cause of elevated blood lactate is physiologically normal rather than pathologic?
    Back
    Strenuous exercise
  57. Front
    Because aldolase splits one six-carbon molecule into two three-carbon pieces, what must you do to every yield from step 6 onward when reporting it per glucose?
    Back
    Multiply by two (everything downstream of the split is doubled per glucose)
  58. Front
    A textbook lists step 6–10 as yielding 1 ATP and 1 NADH. Is that per glucose or per G3P , and what is the per-glucose value?
    Back
    Per G3P ; per glucose it is doubled to 4 ATP and 2 NADH (two G3P per glucose)
  59. Front
    Glucokinase , unlike hexokinases I–III , is NOT inhibited by which molecule, allowing the liver to keep phosphorylating glucose for glycogen storage?
    Back
    Glucose-6-phosphate (G6P)
  60. Front
    Why is it advantageous that glucokinase is not product-inhibited by G6P ?
    Back
    G6P can accumulate without shutting glucokinase off , so the liver keeps trapping glucose and storing it as glycogen after a meal
  61. Front
    From which glycolytic intermediate is 2,3-BPG synthesized in the red blood cell?
    Back
    1,3-bisphosphoglycerate (1,3-BPG)
  62. Front
    Which enzyme diverts 1,3-BPG into the 2,3-BPG shunt in erythrocytes ?
    Back
    Bisphosphoglycerate mutase
  63. Front
    What does the erythrocyte give up by routing 1,3-BPG through bisphosphoglycerate mutase to make 2,3-BPG instead of through phosphoglycerate kinase ?
    Back
    It bypasses phosphoglycerate kinase and forgoes that step's ATP — trading one ATP for better O2 unloading
  64. Front
    What is the aerobic ATP yield FROM GLYCOLYSIS ALONE (before the Krebs cycle), and why is it a range?
    Back
    ~5–7 ATP per glucose ; the range depends on which NADH shuttle is used
  65. Front
    Which NADH shuttle gives the higher glycolysis-alone ATP yield (~7), and which gives the lower (~5)?
    Back
    Malate-aspartate shuttle ~7 ATP ; glycerol-3-phosphate shuttle ~5 ATP
  66. Front
    Glycolysis divides into two phases: the energy investment phase is steps ___ and the energy generation phase is steps ___.
    Back
    Investment = steps 1–5 ; generation = steps 6–10
  67. Front
    How much ATP does the investment phase (steps 1–5) cost, and how much does the generation phase (steps 6–10) yield?
    Back
    Investment costs 2 ATP ; generation yields 4 ATP + 2 NADH ( net 2 ATP, 2 NADH )
  68. Front
    In complete aerobic oxidation of one glucose, how much ATP/reducing equivalent does each stage contribute: glycolysis, pyruvate dehydrogenase , and the Krebs cycle (per glucose)?
    Back
    Glycolysis: 2 ATP + 2 cytosolic NADH; pyruvate dehydrogenase : 2 NADH; Krebs cycle: 6 NADH + 2 FADH2 + 2 GTP
  69. Front
    By what molecular mechanism does fluoride inhibit enolase ?
    Back
    It forms a complex with magnesium and inorganic phosphate that blocks the enzyme's active site
  70. Front
    The phosphoglucose isomerase reaction ( G6P ↔ F6P ) is freely reversible. Why does this matter later?
    Back
    Its reversibility allows the same enzyme to be used (run backward) in gluconeogenesis
  71. Front
    Under AEROBIC conditions, how is the cytosolic NADH from GAPDH (step 6) reoxidized to NAD+ ?
    Back
    It is handed to the malate-aspartate or glycerol-phosphate shuttle and ultimately to the respiratory chain, regenerating NAD+
  72. Front
    By what mechanism does insulin RAISE F2,6BP to accelerate hepatic glycolysis (the mirror of the glucagon /PKA pathway)?
    Back
    Insulin activates a phosphatase that dephosphorylates the PFK-2/FBPase-2 bifunctional protein, switching it to PFK-2 mode, which raises F2,6BP
  73. Front
    Is fructose-2,6-bisphosphate (F2,6BP) an intermediate of glycolysis?
    Back
    No — it is a dedicated regulatory molecule (made by PFK-2 , degraded by FBPase-2 ), not a pathway intermediate

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