Hexokinase/glucokinase, PFK-1 and pyruvate kinase catalyse the three common far-from-equilibrium reactions of mammalian glycolysis.

Which enzyme catalyses glycolysis's committed step after the earlier glucose-6-phosphate branch points?

• Phosphofructokinase-1
• Hexokinase, which forms glucose-6-phosphate before those branches
• Pyruvate kinase, which produces pyruvate in the final glycolytic reaction

What makes a reaction effectively irreversible under the stated cellular conditions?

• A strongly negative delta G that makes direct reverse flux negligible
• A delta G near zero that permits substantial flux in either direction
• The absence of an enzyme, which changes the reaction's equilibrium constant

Citrate rises into an inhibitory range in a PFK-1 assay. Which conclusion is supported?

• Citrate activates PFK-1 and proves every downstream reaction lacks substrate
• Citrate inhibits PFK-1, but does not uniquely diagnose downstream capacity
• Citrate cannot affect PFK-1 unless the citric acid cycle has stopped completely

In a PFK-1 assay, ATP already saturates the catalytic site. Other conditions stay fixed as ATP rises into its inhibitory range. What direct response is expected?

• PFK-1 rate rises because ATP cannot occupy an inhibitory regulatory site
• PFK-1 rate falls through ATP's allosteric inhibition
• PFK-1 rate stays fixed because substrate saturation prevents all regulation

AMP rises in a PFK-1 assay while other conditions remain suitable for catalysis. What direct regulatory response is expected?

• PFK-1 is inhibited because AMP acts like high inhibitory ATP
• PFK-1 is activated as AMP signals increased energy demand
• PFK-1 cannot respond because only ATP-related molecules regulate enzymes

Flux starts at 50 units. Separate matched enzyme-activity reductions give fluxes X: 48, Y: 49, PFK-1: 40, with no off-target effects. Which tested target causes the largest flux decrease?

• Enzyme X, because its final flux of 48 is closest to the starting flux
• Enzyme Y, because its final flux of 49 is the highest measured value
• PFK-1, because its final flux of 40 gives the largest measured decrease

A drug reduces a near-equilibrium enzyme's activity by 20%. No flux measurements or reserve-capacity data are given. A student predicts pathway flux will halve. What follows?

• The flux change cannot be inferred from equilibrium status alone
• Flux must halve because every enzyme has the same share of pathway control
• Flux must stay unchanged because near-equilibrium enzymes can never limit a pathway