A 42-year-old woman with a 10-year history of progressive fatigue, dyspnea on exertion, and recurrent syncope presents to the cardiology clinic. She reports that symptoms worsen with exercise and improve with rest. Cardiac examination reveals a systolic murmur. Echocardiography shows left ventricular hypertrophy with an ejection fraction of 55%. Serum creatine kinase is mildly elevated at 320 U/L. Genetic testing reveals a heterozygous mutation in the COX15 gene (mitochondrial cytochrome c oxidase assembly factor). Which of the following best explains the pathophysiology of her cardiac symptoms?