Connective Tissue
Answers
86.The answer is c.(Alberts, p 1103. Kasper, pp 1481–1484.)The patient
in the scenario suffers from Marfan syndrome, an autosomal dominant dis-
ease in which persons develop abnormal elastic tissue. Decreased elasticity
of lung tissue causes an increased tendency toward spontaneous pneu-
mothorax, also known as a collapsed lung. The aorta is the most affected
organ because of the extensive elastin in the wall, and dissecting aortic
aneurysms are common in these patients. Marfan malformations include
cardiovascular (valve problems as well as aortic aneurysm), skeletal (abnor-
mal height and severe chest deformities), and ocular systems. The molecu-
lar basis of the disease is a mutation in the fibrillin gene. The lens is also
often affected in patients with Marfan syndrome. The result is the disloca-
tion of the lens because of loss of elasticity in the suspensory ligament.
87.The answer is b.(Alberts, pp 1082–1085, 1113–1118.)Theintegrins
are transmembrane heterodimers (integral membrane proteins) that act as
membrane receptors for extracellular matrix components. The best examples
are the fibronectin receptor and the laminin receptor. The receptor structure
includes an intracytosolic portion that binds to the actin cytoskeleton
through the attachment proteins talin or α-actinin. The extracellular portion
has specificity for extracellular matrix molecules. Proteoglycans (answer a)
are located on the extracellular surface of the plasma membrane and
throughout the extracellular matrix. The cadherins (answer c)function as
transmembrane glycoproteins involved in the formation of parts of the
intercellular junctional complexes. Cadherins are components of the
desmosome and zonula adherens. Intermediate filaments and micro-
tubules(answers d and e)are found intracellularly and constitute the
cytoskeleton.
88.The answer is b.(Alberts, pp 1094–1096, 1102–1105. Junqueira, pp 91,
115–116.)Fibronectin is an adhesive glycoprotein that is important for cell
attachment and adhesion. It is important for modulation of cell migration
in the adult and during development. Neural crest and other cells appear
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