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BIO NMDCAT Carbohydrates
nmdcat.online June 27, 2026

Regarding the metabolism of fructose, its entry into the glycolytic pathway in the liver bypasses a key regulatory step catalyzed by phosphofructokinase (PFK-1). This bypass can result in

A. A slower rate of ATP production from fructose compared to glucose
B. An unregulated flux of carbon into glycolysis, potentially promoting fatty acid synthesis
✓
C. The complete inhibition of glycolysis by negative feedback
D. The accumulation of glycogen phosphorylase in the cytosol

📝 Explanation

Fructose is phosphorylated to fructose-1-phosphate, which is cleaved to glyceraldehyde and dihydroxyacetone phosphate, entering glycolysis downstream of PFK-1. This bypasses a critical regulatory checkpoint, allowing a rapid, unregulated influx of carbon that can overload the TCA cycle and lead to increased de novo lipogenesis.

📖 Additional Information

  • A slower rate of ATP production from fructose compared to glucose
  • An unregulated flux of carbon into glycolysis, potentially promoting fatty acid synthesis
  • The complete inhibition of glycolysis by negative feedback
  • The accumulation of glycogen phosphorylase in the cytosol

Fructose is phosphorylated to fructose-1-phosphate, which is cleaved to glyceraldehyde and dihydroxyacetone phosphate, entering glycolysis downstream of PFK-1. This bypasses a critical regulatory checkpoint, allowing a rapid, unregulated influx of carbon that can overload the TCA cycle and lead to increased de novo lipogenesis.

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