Passage
Glycolysis and gluconeogenesis are tightly regulated, opposing metabolic pathways that help control blood glucose levels. Glycolysis converts glucose to two pyruvate molecules, whereas gluconeogenesis consumes 6 ATP equivalents to convert two pyruvate molecules back to glucose. When glycolysis is upregulated, gluconeogenesis is downregulated, and vice versa.As shown in Figure 1, glycolysis and gluconeogenesis in the liver are largely regulated by the allosteric action of the small molecule fructose-2,6-bisphosphate (F2,6BP) on the enzymes phosphofructokinase-1 (PFK-1) and fructose-1,6-bisphosphatase (F1,6BPase) . PFK-1 is a kinase that uses ATP to phosphorylate fructose-6-phosphate (F6P) in an irreversible step of glycolysis, forming fructose-1,6-bisphosphate (F1,6BP) and ADP. During gluconeogenesis, F1,6BPase removes the phosphate group by hydrolysis.
Figure 1 Activities of (A) PFK-1 and (B) F1,6BPase in the presence (solid lines) and absence (dashed lines) of F2,6BPA bifunctional enzyme that contains a phosphofructokinase-2 (PFK-2) domain and a fructose-2,6-bisphosphatase (F2,6BPase) domain controls F2,6BP levels in the liver. The PFK-2 domain converts F6P to F2,6BP, and the F2,6BPase domain converts F2,6BP back to F6P. When blood glucose levels are low, the enzyme becomes phosphorylated. This phosphorylation event simultaneously activates the F2,6BPase domain and inactivates the PFK-2 domain. Under high blood glucose conditions, the enzyme becomes dephosphorylated, activating the PFK-2 domain and inactivating the F2,6BPase domain.
-If one glucose molecule is converted to pyruvate in the muscle and then the resulting pyruvate molecules are converted back to glucose in the liver, what is the net number of ATP equivalents consumed?

Question

Passage
Glycolysis and gluconeogenesis are tightly regulated, opposing metabolic pathways that help control blood glucose levels. Glycolysis converts glucose to two pyruvate molecules, whereas gluconeogenesis consumes 6 ATP equivalents to convert two pyruvate molecules back to glucose. When glycolysis is upregulated, gluconeogenesis is downregulated, and vice versa.As shown in Figure 1, glycolysis and gluconeogenesis in the liver are largely regulated by the allosteric action of the small molecule fructose-2,6-bisphosphate (F2,6BP) on the enzymes phosphofructokinase-1 (PFK-1) and fructose-1,6-bisphosphatase (F1,6BPase) . PFK-1 is a kinase that uses ATP to phosphorylate fructose-6-phosphate (F6P) in an irreversible step of glycolysis, forming fructose-1,6-bisphosphate (F1,6BP) and ADP. During gluconeogenesis, F1,6BPase removes the phosphate group by hydrolysis.

Figure 1 Activities of (A) PFK-1 and (B) F1,6BPase in the presence (solid lines) and absence (dashed lines) of F2,6BPA bifunctional enzyme that contains a phosphofructokinase-2 (PFK-2) domain and a fructose-2,6-bisphosphatase (F2,6BPase) domain controls F2,6BP levels in the liver. The PFK-2 domain converts F6P to F2,6BP, and the F2,6BPase domain converts F2,6BP back to F6P. When blood glucose levels are low, the enzyme becomes phosphorylated. This phosphorylation event simultaneously activates the F2,6BPase domain and inactivates the PFK-2 domain. Under high blood glucose conditions, the enzyme becomes dephosphorylated, activating the PFK-2 domain and inactivating the F2,6BPase domain.
-If one glucose molecule is converted to pyruvate in the muscle and then the resulting pyruvate molecules are converted back to glucose in the liver, what is the net number of ATP equivalents consumed?

Quizplus · Accepted Answer

11ecba2d_0f0e_1b20_a3bf_7d135a8649b0_MD0008_00 Metabolism consists of both catabolic and anabolic pathways. Catabolic pathways degrade complex molecules into simpler molecules to produce high-energy molecules, such as ATP. ATP provides energy for many biological processes, including muscle contraction. Anabolic pathways use simple molecules (eg, amino acids, sugars) as precursors to synthesize more complex molecules (eg, proteins, polysaccharides). Anabolism requires energy input from ATP or similar molecules such as GTP (ie, ATP equivalents). Most catabolic processes are paired with an opposing anabolic process. Glycolysis is a catabolic process that degrades glucose to pyruvate. For every glucose molecule that completes glycolysis, a net total of two ATP molecules are produced (2 consumed and 4 generated). In contrast, gluconeogenesis is an anabolic process. According to the passage, gluconeogenesis requires the net input of 6 ATP equivalents (2 GTP and 4 ATP) to produce one glucose molecule. Glycolysis in the muscles is connected to gluconeogenesis in the liver by the Cori cycle. In this scenario, one glucose molecule is converted to two pyruvate molecules in the muscle, which are then sent to the liver (as lactate), where they are converted back to glucose. Because gluconeogenesis consumes 6 net ATP equivalents and glycolysis produces 2 net ATP equivalents, a net total of 4 ATP equivalents are consumed in one round of the cycle. (Choice A) Glycolysis produces 2 ATP equivalents per glucose molecule, but these ATP molecules, as well as 4 others, are consumed by gluconeogenesis. (Choice C) Gluconeogenesis consumes a total of 6 ATP equivalents, but in the given scenario, glycolysis also produces 2 equivalents, so the net result is the consumption of 4 ATP equivalents. (Choice D) If glycolysis resulted in the net consumption of 2 ATP equivalents, the overall process would require 8 ATP equivalents. However, glycolysis results in the net production of 2 ATP equivalents. Educational objective: Catabolic processes lead to energy production, typically in the form of ATP equivalents. In contrast, anabolic processes consume energy. Glycolysis (a catabolic process) and gluconeogenesis (an anabolic process) are connected by the Cori cycle.

Passage Glycolysis and Gluconeogenesis Are Tightly Regulated, Opposing Metabolic Pathways That