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THE CELL

1. A pediatric endocrinologist conducts a new patient exam on a 3-year-old boy who exhibits unusual symptoms. His parents state that they carefully monitor his diet and give him a daily multivitamin as directed, but despite their care, he has continued to gain weight and is now at the 99th percentile of the weight curve. On exam, he has puffy facial features and appears lethargic. Furthermore, basic cognitive tests indicate he is developmentally delayed. Based on these symptoms, the physician worries about a thyroid hormone deficiency. Which of the following proteins is most critical for thyroid hormone signaling?

A. Blood-brain barrier (BBB) integrity protein

B. Mitochondrial receptor

C. Nuclear receptor

D. Plasma membrane channel protein

E. Plasma membrane pump

F. Post-translational modification protein

(C) Thyroid hormones enter the cell and signal directly within the nucleus. This is distinct from steroid hormones, which bind a receptor in the cytosol and are then transported to the nucleus; and protein hormones such as parathyroid hormone, which bind receptors on the plasma membrane and induce signaling within the cell without actually entering the cell. Because thyroid hormones bind their receptor directly in the nucleus, none of the other answer choices describe a step in the thyroid signaling pathway. [Section 4.b]

2. A 16-year-old patient presents to her primary care physician after returning home after a spring break school trip to South America 2 weeks ago. Soon after she returned, she developed a runny nose and persistent sneezing. She has been getting headaches and is having trouble sleeping. She states she is worried about a respiratory infection and says that school friends do not want to be near her because they say she has “tuberculosis.” The physician, however, suspects seasonal allergies. He recommends she take an over-the-counter (OTC) antihistamine to see if it improves her symptoms. He recommends loratadine, a second-generation antihistamine, for daytime, and diphenhydramine, a first-generation drug of the same class, for nighttime. Which of the following statements is most likely true about these drugs given his recommendations?

A. Diphenhydramine blocks neuronal signaling more readily than loratadine

B. Diphenhydramine is metabolized by the liver more rapidly than loratadine

C. Loratadine crosses the blood-brain barrier more readily than diphenhydramine

D. Loratadine has a higher effective dose than diphenhydramine

E. Loratadine is more lipophilic than diphenhydramine

(A) First-generation antihistamines are nonpolar molecules, meaning they are not ionized and do not carry a charge, and they do not have a strong ...

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