A 55-year-old male presents with progressive memory loss, confusion, and difficulty performing daily tasks over the past 3 years. Neurological examination reveals cognitive impairment and mild motor dysfunction. MRI shows cortical atrophy, and cerebrospinal fluid (CSF) analysis detects elevated tau protein and β-amyloid plaques. The pathophysiology of this patient’s disease involves protein misfolding and aggregation. Which of the following molecular chaperones plays a major role in preventing the accumulation of misfolded proteins in neurodegenerative diseases like Alzheimer’s?

A 30-year-old woman presents with muscle weakness and fatigue. Laboratory tests reveal elevated creatine kinase levels and myoglobinuria. Her physician suspects rhabdomyolysis and explains that myoglobin, a protein with a tertiary structure, is released from damaged muscle cells. The physician contrasts myoglobin’s structure with hemoglobin’s quaternary structure. Which of the following best describes the difference between hemoglobin and myoglobin in terms of protein structure and oxygen binding?

A 65-year-old man with a long-standing history of chronic obstructive pulmonary disease (COPD) presents to his physician with worsening shortness of breath and fatigue. He reports that his symptoms have progressively worsened over the past few months, and he now struggles to perform daily activities like walking short distances or climbing stairs. On examination, his oxygen saturation is 85% on room air, and arterial blood gas (ABG) analysis reveals hypoxemia (PaO₂ = 60 mmHg) with a normal pH. His physician explains that his symptoms are due to impaired oxygen delivery, which is influenced by hemoglobin’s ability to bind and release oxygen. The physician further explains that hemoglobin’s quaternary structure plays a critical role in optimizing oxygen delivery to tissues. Which of the following best explains how hemoglobin’s quaternary structure enhances oxygen delivery to tissues?

A 25-year-old African American man with a known history of sickle cell disease (SCD) presents to the emergency department with severe pain in his chest and lower limbs. The pain began shortly after he completed a long-haul flight. He describes the pain as sharp and throbbing, and it is not relieved by over-the-counter pain medications. He also reports feeling fatigued and short of breath. On physical examination, he appears pale and in distress. His vital signs show tachycardia and mild hypoxia. Laboratory tests reveal low hemoglobin (Hb) levels and the presence of sickled red blood cells on a peripheral blood smear. Based on his history, symptoms, and lab findings, he is diagnosed with a vaso-occlusive crisis (VOC), a common complication of sickle cell disease. Which of the following best describes the role of hemoglobin’s quaternary structure in this patient’s condition?

A newborn male is admitted to the neonatal ICU with meconium ileus, recurrent lung infections, and failure to thrive. Genetic testing reveals a homozygous ΔF508 mutation in the CFTR gene, leading to a diagnosis of cystic fibrosis. The physician explains that this mutation causes improper folding of the CFTR protein, preventing its trafficking to the cell membrane. Which of the following molecules is most responsible for assisting protein folding and preventing misfolded protein aggregation in the cell?

A 35-year-old woman presents with dry, brittle hair and frequent skin infections. She has a history of mild intellectual disability. Laboratory tests reveal low serum copper levels, and genetic testing confirms a mutation in the ATP7A gene, consistent with Menkes disease. The physician explains that copper is required for enzymes that stabilize protein structure, including those involved in disulfide bond formation. Which of the following interactions is most responsible for maintaining the stability of tertiary protein structure in extracellular proteins like keratin and antibodies?