Items 23-30

For each numbered biochemical description of an extracellular matrix moledule or its receptor, choose the most appropriate lettered molecule. Answers may be used once, more than once, or not at all.

(A) Collagen
(B) Fibronectin
(C) Laminin
(D) Chondrotin sulfate
(E) Heparan sulfate
(F) Hyaluronic acid
(G) Integrin
(H) Elastin
(I) Fibrillin

23. This molecule is composed of subunits assembled into a cruciform aggregate. It binds to heparan sulfate, proteoglycan and type IV collagen. It s an essential structural component of many basement membranes.

24. This molecule is a gylcosaminoglycan that has a MW = 1,000,000 or more. It forms the backbone of cartilage proteoglycan aggregates.

25. This molecule typically has approximately 1/3 of its amino acids as gylcine and is also rich in praline. In some cases, it forms striated fibrillar aggregates.

26. This molecule forms anastomosing molecular chains. Upon hydrolysis, it releases the usually amino acid desmosine.

27. This molecule is an important cell adhesion protein. It has a MW = 460,000 and contains two separate polypeptides chains of MW = 230,000 cross-linked by S – S – bridges;

28. This molecule is a heterodimeric transmembrane glycoprotein. Different forms exist for recognition of fibronectin and laminin.

29. This molecule is a glycosaminoglycan with a repeating disaccharide containing N-acetyl-D-galactosamine and D-glucuronic acid.

30. This is the most abundant protein in the human body.

ANSWERS AND TUTORIAL ON ITEM 23-30

The answers are: 23-C;24-F;25-A;26-H;27-B; 28-G;29-D;30-A Collagen (A) is the most abundant protein in the human body. It exists in fubruos, laminar and amorphous form. Collagen consists of subunit molecules with three helically intertwined a chains of many different types and combinations of chains. Each a chain is a polypetide with 1/3 of the residues as glycine; it is relatively rich in praline and lysine.

Fibronectin (B) is a MW = 460,000 glycoprotein of two similar subunits bound together by – S – S – bridges. It exists in two forms. The cellular form is widely distributed in cells of the connective tissues and on cell surface. It has several distinct domains that are involved in binding cell to the collagenous extracellular matrix of connective tissue. The plasma from is dissolved in blood and is involved in the clotting mechanism because of its ability to bind to platelets and to the serum protein fibrin.

Laminin (C) is an important component of the basement of two different polypeptide epithelial cells. This molecule, a large glycoprotein, is composed of two different polypeptide chains with MW = 220,000 and 440,000 assembled into a cruciform aggregate. It binds to herpana sulfate, proteoglycan and type IV collagen.

Chondrotin sulfate (D) is a glycosaminoglycan of a repeating disaccharide units with D-glucuronic acid and N-acetly-D-galactosamine sulfated at the 4 or 6 positions. It is abundant in hyaline and elastic cartilage where it forms a key component of cartilage proteoglycan.

Heparan sulfate (E) is a glyconsaminoglycan composed of a repeating disaccharide unit with D-glucuronic acid (or iduronic acid) and N-acetyl-D-glucosamine (or glucosamine). It is sulfated, but less so than the closely related compound heparin. It is found in blood vessel walls, associated with reticular fibers, in the brain and on the surface of many cells.

Hyaluronic acid (F) is a glycosaminoglycan composed of a repeating disaccharide unit with D-glucuronic acid and N-acetyl –D-glucosamine. Unlike other glycosaminoglycans, it can be found free in the extracellular matrix. It is also an important component of cartilage proteoglycan. It is an extenden polymer, often with a MW > 1,000,000.

The integrins (G) form a complex family of intergral membrane proteins.Each district integrin contains different types of a and ? subunits which are assembled in many different combinations to confer ligand specificity on the itegrin. It is a cell surface receptor for many different extracellular matrix glycoproteins including fibronectin and laminin. Integrins are transmembrane proteins involved in signal transduction from the exterior to the interior of many cells.

Elastin (H) is a complex polypeptide found in abundance in elastic fibers. About 30% of its amino acids are glycine and it is also rich in praline and lysine. Several different lysine residues are chemically modified and then convalently bound together to form cross-links which, when hydrolyzed, yield the unusual amino acids desmosine and isodesmosine.

Fibrillin (I) is a glycoprotein with MW = 350,000. It forms a major component of 8-10 nm beaded extracellular fibrils. These are often closely associated with elastic fibers of the basement membrane. Forensic Comparison Microscopes, Inverted Tissue Culture Microscopes, Metallurgical Microscopes Ore Microscopes