Question

Explain how the Cori cycle leads to the regeneration of NAD+and production of glucose for muscles with an active glycolysis pathway.

As in glycolysis and the degradation of glucose, the degradation of fatty acids also requires an initial investment of ATP energy. State the reaction or reactions where ATP energy is needed before fatty acids can be oxidized.

Answer 1

1. Cori cycle is a metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is cyclically metabolized back to lactate. During intense muscular exercise, oxygen is not sufficient to continue aerobic respiration and muscles switch on to anaerobic respiration or lactate fermentation where pyruvate produced during glycolysis is converted to lactate.  This regenerates NAD⁺, maintaining the NAD⁺ concentration so that additional glycolysis reactions can occur.  This occurs as fermentation transfers two electrons from NADH to reduce pyruvate into lactate and thus NAD+ is regenerated.

2. Fatty acids must be converted to an active intermediate before they can be catabolized. This is the only step in the complete degradation of a fatty acid that requires energy from ATP. The activation of fatty acid is completed in two steps-

Fatty acid + ATP Acyl adenylate + PPi

Acyl adenylate + HS - CoA Acyl CoA + AMP