Glycolysis vs Gluconeogenesis
How to tell Glycolysis and Gluconeogenesis apart when a board question makes them look alike.
Glycolysis consumes glucose and uses PFK-1; gluconeogenesis makes glucose and bypasses irreversible steps with PC, PEPCK, F-1,6-BPase, and G6Pase.
Side by side
Glycolysis breaks glucose down to pyruvate, produces ATP and NADH, is activated by insulin and AMP/fructose-2,6-bisphosphate, and uses PFK-1 as key regulated step.
Gluconeogenesis synthesizes glucose from lactate, alanine, glycerol, or propionate, is activated by glucagon/cortisol, and uses pyruvate carboxylase, PEPCK, fructose-1,6-bisphosphatase, and glucose-6-phosphatase.
Cytosolic glycolytic enzymes convert glucose to pyruvate, with irreversible steps catalyzed by hexokinase/glucokinase, PFK-1, and pyruvate kinase.
Gluconeogenesis bypasses irreversible glycolysis steps using mitochondrial and cytosolic enzymes, mainly in liver and kidney.
High insulin, fed state, PFK-1 activation, pyruvate kinase activity, and ATP production support glycolysis.
Fasting, glucagon, acetyl-CoA activation of pyruvate carboxylase, and fructose-1,6-bisphosphatase support gluconeogenesis.
The trap
They are not simple reverses; the irreversible steps use different enzymes and reciprocal regulation.
Watch it explained
Test it nowThe repair move
For glucose metabolism, identify fed versus fasting state and the regulated irreversible enzyme.
Try a free question
CoreA research team is studying the rate-limiting enzyme of glycolysis. They observe that this enzyme is activated by AMP, citrate's antagonist fructose 2,6-bisphosphate, and that high citrate and ATP levels inhibit it. Which enzyme is being studied?
Show answer and explanation
Answer: A. Phosphofructokinase-1 (PFK-1). PFK-1 is the rate-limiting enzyme of glycolysis; activated by AMP and fructose 2,6-bisphosphate (insulin signal); inhibited by ATP, citrate, and glucagon (via decreased F2,6BP); catalyzes the committed step of glycolysis: fructose 6-phosphate -> fructose 1,6-bisphosphate.
Why the other choices are tempting
- B. Glucose-6-phosphatase is the final step of gluconeogenesis and glycogenolysis in liver.
- C. Pyruvate carboxylase is the first committed step of gluconeogenesis (pyruvate to oxaloacetate).
- D. Fructose 1,6-bisphosphatase is the gluconeogenic counter-regulatory enzyme of PFK-1.
- E. Hexokinase phosphorylates glucose but is not the rate-limiting glycolytic step.
Flashcards
Tap a card to flip it.
What is the committed glycolysis enzyme?
PFK-1 is the committed regulated glycolysis enzyme.
What enzyme bypasses PFK-1 in gluconeogenesis?
Fructose-1,6-bisphosphatase bypasses PFK-1 during fasting hepatic glucose production.
Quick answers
What is the fastest way to tell Glycolysis from Gluconeogenesis?
Glycolysis consumes glucose and uses PFK-1; gluconeogenesis makes glucose and bypasses irreversible steps with PC, PEPCK, F-1,6-BPase, and G6Pase.
What is the key clue for Glycolysis?
Glycolysis breaks glucose down to pyruvate, produces ATP and NADH, is activated by insulin and AMP/fructose-2,6-bisphosphate, and uses PFK-1 as key regulated step.
What is the key clue for Gluconeogenesis?
Gluconeogenesis synthesizes glucose from lactate, alanine, glycerol, or propionate, is activated by glucagon/cortisol, and uses pyruvate carboxylase, PEPCK, fructose-1,6-bisphosphatase, and glucose-6-phosphatase.
What is the common trap with Glycolysis vs Gluconeogenesis?
They are not simple reverses; the irreversible steps use different enzymes and reciprocal regulation.