How glycolysis responds to regulation

Science · Biochemistry & Molecular Biology · ages 19-21

Name ______________________ Date ____________

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

Answer key

For grown-ups. Fold this page away before handing over the rest.

How glycolysis responds to regulation W1-mt_2vAoKtnmoz-s1

True · These are glucose phosphorylation, fructose-6-phosphate phosphorylation and phosphoenolpyruvate conversion to pyruvate.
Phosphofructokinase-1 · PFK-1 forms fructose-1,6-bisphosphate after intermediates that can enter other pathways.
A strongly negative delta G that makes direct reverse flux negligible · Strongly negative delta G strongly favours forward conversion under those conditions.
Citrate inhibits PFK-1, but does not uniquely diagnose downstream capacity · Citrate's direct inhibitory effect is supported, but it does not uniquely identify downstream pathway capacity.
PFK-1 rate falls through ATP's allosteric inhibition · Beyond its substrate role, high ATP can inhibit PFK-1 allosterically.
PFK-1 is activated as AMP signals increased energy demand · AMP can activate PFK-1. Whole-pathway flux is a separate, condition-dependent outcome.
PFK-1, because its final flux of 40 gives the largest measured decrease · The decreases are 2 for X, 1 for Y and 10 for PFK-1. PFK-1 has the strongest effect in this test.
The flux change cannot be inferred from equilibrium status alone · Neither halving nor no change follows from near-equilibrium status alone.