Fates of Pyruvate

Pyruvate

A 3-carbon molecule produced during the final step of glycolysis.

Fate of pyruvate

The fate of pyruvate depends largely on whether oxygen is available.

Anaerobic metabolism

Metabolism that occurs when oxygen is unavailable or insufficient; pyruvate is converted to lactate.

Aerobic metabolism

Metabolism that occurs when oxygen is available; pyruvate can enter the citric acid cycle for further energy production.

Anaerobic fate of pyruvate

Pyruvate is converted to lactate when oxygen is insufficient.

Lactate

The product formed when pyruvate is converted during anaerobic metabolism.

Lactate dehydrogenase (LDH)

The enzyme that converts pyruvate to lactate while allowing NAD⁺ to be regenerated.

Purpose of lactate formation

Regenerating NAD⁺ allows the ATP-generating steps of glycolysis to continue when oxygen is insufficient.

NAD⁺ regeneration

The conversion of pyruvate to lactate regenerates NAD⁺ from NADH, allowing glycolysis to continue producing ATP.

Anaerobic ATP production

Glycolysis can continue producing ATP without oxygen as long as NAD⁺ is regenerated.

Cori cycle

A metabolic cycle in which lactate produced by tissues is transported to the liver, where it can be converted back into glucose.

Lactate in the liver

The liver can use lactate to produce glucose through gluconeogenesis.

Lactate → glucose pathway

Lactate travels to the liver → converted to glucose → glucose can return to tissues for energy.

Lactic acid/lactate buildup during exercise

During strenuous exercise, oxygen delivery may not keep up with the muscles' demand, increasing reliance on anaerobic glycolysis and lactate production.

Oxygen delivery during strenuous exercise

During very intense exercise, the respiratory and cardiovascular systems may not deliver oxygen to working muscles quickly enough to meet their energy demands.

Leg muscles and anaerobic metabolism

Leg muscles can be particularly affected during strenuous exercise because of their high energy demands.

Effects associated with strenuous exercise

Lactate accumulation and the increased metabolic demands of intense exercise are associated with muscle fatigue; muscle pain can also occur with strenuous exercise.

Preventing exercise-related problems

Gradually increase activity level, pace, and distance rather than increasing intensity too quickly.

Antioxidants and exercise

Antioxidants have been discussed as a potential way to combat oxidative stress associated with exercise.

Aerobic fate of pyruvate

When oxygen is available, pyruvate proceeds into aerobic metabolism and ultimately enters the citric acid cycle.

Pyruvate and the citric acid cycle

Pyruvate is converted to acetyl-CoA, which then enters the citric acid cycle.

Pyruvate → acetyl-CoA

Before entering the citric acid cycle, pyruvate undergoes pyruvate decarboxylation to form acetyl-CoA.

Purpose of aerobic pyruvate metabolism

Allows glucose-derived carbon to enter the citric acid cycle and continue through oxidative pathways to generate more energy.

Alcoholic fermentation

An anaerobic pathway that converts carbohydrate-derived compounds into alcohol and carbon dioxide.

Where alcoholic fermentation occurs

Occurs primarily in yeast and other carbohydrate-fermenting organisms.

Product of alcoholic fermentation

Produces ethanol (alcohol) and carbon dioxide.

Alcoholic vs. lactic fermentation

Humans primarily use lactate formation to regenerate NAD⁺ during anaerobic glycolysis, while yeast can use alcoholic fermentation.