Chapter 4 - Extracellular Matrix

Question 1

Which one of the following statements about the fibronectin receptor is true?
(A) It is located exclusively in the basal lamina.
(B) It is a cross-shaped glycoprotein.
(C) It mediates the linkage of molecules out­
side the cell with cytoskeletal elements
inside the cell.
(D) It belongs to the entactin family of receptors.
(E) Its absence is associated with scurvy.

Answer 1

C. The fibronectin receptor is a transmembrane protein that enables cells to adhere to the ECM. Laminin is a cross-shaped glycoprotein in the basal lamina, where entactin is also present (see Chapter 4 II D).

Question 2

Which one of the following events in collagen synthesis occurs outside of the cell?
(A) Synthesis of preprocollagen
(B) Hydroxylation oflysine residues
(C) Triple-helix formation
(D) Carbohydrate addition to procollagen
(E) Cleavage ofprocollagen by procollagen
peptidases

Answer 2

E. In the extracellular space, peptidases cleave offend sequences of procollagen to yield tropo­collagen, which self-assembles to form collagen fibrils (see Chapter 4 III A 1).

Question 3

A medical student goes to the emergency department and is diagnosed with a ruptured bowel, the result of a genetic condition called Ehlers-Danlos type IV syndrome. Which one of the following statements about this patient’s condition is true?
(A) He has a defect in the synthesis of mRNA encoding type I collagen.
(B) He has a defect in the genes encoding type IV collagen.
(C) He has defective type II collagen.
(D) He has an increased risk of breaking his
bones.
(E) He has a defect in the translation of mRNA for type III collagen.

Answer 3

E. Ehlers-Danlos type IV syndrome is associated with a defect in the synthesis and translation of mRNA for type III reticular collagen (see Chapter 4 III A 1 Clinical Considerations).

Question 4

Which one of the following statements about hyaluronic acid is true?
(A) It is a component of elastic fibers.
(B) It is a glycosaminoglycan.
(C) It is a proteoglycan with a shape resem­bling a bottlebrush.
(D) It is sulfated.
(E) It is a small molecule.

Answer 4

B. Hyaluronic acid is a glycosaminoglycan, not a proteoglycan. The core protein of proteogly­cans can attach to hyaluronic acid forming large aggregates (see Chapter 4 II A).

Question 5

Which one of the following statements about osteonectin is true?
(A) It is present in the lacunae of bone.
(B) It is a proteoglycan.
(C) It binds to type II collagen.
(D) It influences calcification of bone.
(E) It is synthesized by osteoclasts.

Answer 5

D. Osteonectin synthesized by osteoblasts influences the calcification of bone and binds to type I collagen in the bone matrix. Type II collagen is found in cartilage (see Chapter 4 II C).

Question 6

Which of the following statements about scurvy is true?
(A) One of its symptoms is bowlegs.
(B) It is caused by excessive glycosylation of tropocollagen.
(C) It is caused by a deficiency of vitamin A.
(D) It is associated with structurally defective
elastic fibers.
(E) It is alleviated by eating citrus fruits.

Answer 6

E. Scurvy is caused by a deficiency of vitamin C, a necessary cofactor in the hydroxylation of preprocollagen. Citrus fruits are rich in vitamin C (see Chapter 4 III A 1 Clinical Considerations).

Question 7

Which one of the following is a glycoprotein across which fibroblasts migrate during wound healing?
(A) Fibrillin
(B) Fibronectin
(C) Elastin
(D) Entactin
(E) Laminin

Answer 7

B. Fibronectin forms tracks along which cells migrate. During wound healing in connec­tive tissue, fibroblasts adhere to fibronectin in blood clots, facilitating the healing process (see Chapter 4 II C 1 Clinical Considerations).

Question 8

Which of the following is an adhesive glycoprotein that links type IV collagen with laminin in the lamina densa?
(A) Fibrillin
(B) Fibronectin
(C) Elastin
(D) Entactin
(E) Tenascin

Answer 8

D. Entactin is a sulfated adhesive glycoprotein in basal and external laminae that binds both type IV collagen and laminin (see Chapter 4 II C).

Question 9

Which one of the following is a main component of peripheral microfibrils in an elastic fiber?
(A) Fibrillin
(B) Fibronectin
(C) Elastin
(D) Entactin
(E) Laminin

Answer 9

A. Fibrillin is the major component of the peripheral microfibrils of elastic fibers (see Chapter 4 III B).

Question 10

Which one of the following is present in the basement membrane and is manufactured by connective tissue cells?
(A) Fibrillin
(B) Fibronectin
(C) Elastin
(D) Entactin
(E) Laminin

Answer 10

B. Fibronectin is synthesized by cells of the connective tissue, usually fibroblasts, and is located in the lamina reticularis near the lamina densa (see Chapter 4 II C 1).