A 17-year old girl was brought to the hospital after suffering an apparent seizure during gym class. Blood tests indicated elevated levels of lactic acid. Melissa was a full-term infant, but displayed difficulties developing a suckling response and often measured a height/weight index lower than most babies her age. During elementary school, her mother noted to their pediatrician that Melissa’s eyelids appeared droopy and she complained of difficulties focusing her vision. At 13, Melissa tried out for a local soccer team, but found it difficult to maintain the exercise pace required during practices, feeling winded and complaining of leg cramps. Her pediatrician attributed her symptoms to asthma and prescribed a regimen of steroid inhalers. As Melissa began high school, her asthma symptoms progressively worsened, especially during gym class. She complained more frequently of muscle cramps and she required stronger corrective eye glasses, found it increasingly difficult to maintain focus on her school work. a. What cellular structure is defective, missing, or malfunctioning?