Phosphofructokinase-1 (PFK-1) is the primary regulatory enzyme of glycolysis. Which condition would most strongly ACTIVATE PFK-1?
AHigh ATP and high citrate levels
BHigh AMP and low ATP levels
CHigh glucose-6-phosphate levels
DLow inorganic phosphate (Pi) levels
AMP signals low cellular energy. PFK-1 is allosterically inhibited by high ATP and citrate (which signal energy abundance) and activated by AMP and ADP. When AMP is high, the cell is energy-depleted and glycolysis should accelerate to restore ATP.
Question 2 True / False
Glycolysis cannot occur without oxygen because it requires aerobic respiration to regenerate the NAD⁺ consumed in the GAPDH reaction.
TTrue
FFalse
Answer: False
Glycolysis is entirely anaerobic. NAD⁺ can be regenerated without oxygen through fermentation — lactate production in muscle cells or ethanol fermentation in yeast. Oxygen is required only for the electron transport chain, which operates downstream of glycolysis.
Question 3 Short Answer
Why does glycolysis produce a net yield of only 2 ATP per glucose, even though 4 ATP are generated in the payoff phase?
Think about your answer, then reveal below.
Model answer: Two ATP are consumed in the investment phase (steps 1 and 3) to phosphorylate glucose and fructose-6-phosphate. The net yield is therefore 4 ATP generated minus 2 ATP invested = 2 ATP per glucose.
The investment phase phosphorylates glucose to make intermediates reactive and to trap them inside the cell. This energetic cost is unavoidable — the phosphorylation steps prime glucose for the aldol cleavage and subsequent energy-releasing reactions of the payoff phase.