A 15-year-old boy presents with shortness of breath on exertion for the past 2 weeks. Although he does not have any other complaints, he is concerned about not gaining much weight despite a good appetite. His height is 188 cm (6 ft 2 in) and weight is 58 kg (124 lb). His blood pressure is 134/56 mm Hg and his pulse rate is 78/min. On cardiac auscultation, his apex beat is displaced laterally with a diastolic murmur lateral to the left sternal border. Slit-lamp examination shows an upward and outward displacement of both lenses. Synthesis of which of the following proteins is most likely defective in this patient?
AFibronectin
BElastin
CFibrillin
DReticular fibers
ELaminin
Collagen is a very critical structural protein in many of our connective tissues. Defects in collagen produce diseases such as Ehlers-Danlos syndrome, where there is a defective lysyl hydroxylase gene, or osteogenesis imperfecta, where there is a defect in the production of type I collagen. Which of the following represents the basic repeating tripeptide of collagen?
AGly-X-Y
BAsp-X-Y
CMet-X-Y
DSer-X-Y
EGlu-X-Y
A 62-year-old man with prostate cancer comes to the physician because of low back pain for 2 weeks and a 4.5-kg (10-lb) weight loss. Physical examination shows localized tenderness over the lumbar spine. An x-ray of the lumbar spine shows several osteoblastic lesions at the level of L2 and L4 vertebrae. Microscopic examination of a bone biopsy specimen from the L4 vertebra shows irregular bone trabeculae and star-shaped cells with long, cytoplasmic processes located deep within the lacunae. Exchange of nutrients and waste products between these cells most likely occurs through which of the following structures?
AZonula adherens
BMacula adherens
CMacula communicans
DZonula occludens
EHemidesmosomes
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