This is the "ring/married" step because ___________________

This step is _____________.

The product made is ______________.

Question

This is the "ring/married" step because ___________________

This step is _____________.

The product made is ______________.

BlackTom AI · Accepted Answer

Phosphofructokinase-1 (PFK-1) catalyzes the conversion of fructose-6-phosphate (F6P) to fructose-1,6-bisphosphate (F1,6BP) using ATP; this reaction is the committed, highly regulated step of glycolysis.

1) Relevant knowledge points and concepts
- PFK-1 reaction: F6P + ATP → F1,6BP + ADP (requires Mg2+).  
- Thermodynamics: strongly exergonic in vivo (ΔG°′ negative; image shows ~–14 kJ/mol), making the step effectively irreversible.  
- Commitment: formation of F1,6BP channels carbohydrate flux into glycolysis because F1,6BP is the substrate that will be cleaved by aldolase into triose phosphates; it cannot readily be used for reversal to glucose or diverted to glycogen synthesis.  
- Regulation: PFK-1 is the major rate-limiting, allosterically controlled enzyme of glycolysis (inhibited by ATP and citrate, activated by AMP and fructose-2,6-bisphosphate).

2) Step-by-step reasoning
- The enzyme depicted plus ATP and Mg2+ and a negative ΔG indicates an irreversible ATP-dependent phosphorylation.  
- The product that carries two phosphate groups (bisphosphate) fits F1,6BP chemically.  
- Because that phosphorylation commits the molecule to cleavage into 3-carbon intermediates, the pathway is committed to glycolysis after this step.  
- The large negative ΔG and known regulatory role identify the step as heavily regulated.

3) Calculations
- No arithmetic calculation required; thermodynamic sign (negative ΔG) and consumption of one ATP are the key quantitative facts.

4) Why the correct answer is correct
- The statement “the product is committed to glycolysis, heavily regulated, F1,6BP” directly describes the PFK-1 step: commitment to glycolysis (irreversible phosphorylation), heavy allosteric regulation, and product identity F1,6BP.

5) Why other options are incorrect
- “Product trapped inside cell, not regulated, F6P”: trapping inside cell describes hexokinase (G6P), but that step is regulated and the described product (F6P) is the substrate here, not the committed product.  
- “Committed to glycolysis, heavily regulated, F6P”: wrong product—F6P is converted, not produced.  
- “Committed to glycogen storage, heavily regulated, F1,6BP”: F1,6BP commits to glycolysis, not glycogen synthesis.

6) Conclusion
- Therefore the correct choice is: the product is committed to glycolysis, heavily regulated, F1,6BP, which matches the provided answer.

This is the "ring/married" step because _____________ This step is _. The product made is ________.单项选择题

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This is the "ring/married" step because ___________________ This step is _____________. The product made is ______________.单项选择题