Metabolism & Bioenergetics MCAT Practice Question
A 24-year-old male sprinter performs a maximal 400-meter sprint. During the first 10 seconds, muscle phosphocreatine is depleted. He continues sprinting for an additional 50 seconds, relying almost exclusively on anaerobic glycolysis. Blood lactate rises from 2 mmol/L at rest to 18 mmol/L at the finish line. A colleague questions how glycolysis can continue at such high rates when lactate is accumulating to toxic levels. Which of the following best explains the paradox of high lactate production enabling continued ATP generation during intense anaerobic exercise?
Answer choices
- ALactate directly binds to and allosterically activates phosphofructokinase-2, increasing glycolytic flux
- BLactate is rapidly oxidized by lactate oxidase in mitochondria, generating more ATP than glycolysis alone
- CLactate formation from pyruvate regenerates NAD+, allowing continued oxidation of glyceraldehyde-3-phosphate in glycolysisCorrect answer
- DLactate acts as a proton buffer, neutralizing H+ ions and preventing inhibition of glycolytic enzymes by acidosis
- ELactate binds to the glucose transporter GLUT4, increasing glucose uptake into working muscle
- FLactate suppresses fatty acid oxidation, allowing glucose to be the exclusive fuel source
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