(3) Chapter 15: Cell Walls, the Extracellular Matrix, and Cell Interactions

Question 1

Basal laminae

Answer 1

• thin layers on which epithelial cells rest.

- surrounds muscle cells, adipose cells, and peripheral nerves

Question 2

Connective tissues

Answer 2

loose connective tissue, bone, tendon, cartilage

• consists mostly of extracellular matrix with cells distributed throughout.
• extracellular matrix is very abundant

Question 3

Extracellular matrices

Answer 3

• have tough proteins embedded in a gel-like polysaccharide

- most abundant in connective tissue

Question 4

Adhesion proteins

Answer 4

link components of the matrix to one another and to cells

Question 5

Compare types of matrices on the amounts of components

Answer 5

a) . tendons: high proportion of fibrous proteins
b) cartilage: high level of polysaccharides that form a compression-resistant gel
c) bone matrix is hardened by calcium phosphate crystals

Question 6

Collagen

Answer 6

a) major structural protein

b) structure: 3 polypeptide chains in a triple helix

Question 7

Describe AA acid sequence of collagen

Answer 7

• each triple helix domain consists of an AA sequence with a Glycine in every 3rd position (Gly-X-Y)
• glycine is the smallest amino acid so it’s position allows the polypeptides to closely pack together.
• Proline in frequently in the X position
• Hydroxyproline is frequently in the Y position : it’s hydroxy groups are thought to stabilize the III helix by forming H-bonds

Question 8

How is hydroxyproline formed?

Answer 8

-formed in the ER by modification of proline in collagen polypeptide chains

Question 9

Type 1 collagen

Answer 9

• most abundant
• Forms collagen fibrils in which the triple helixal molecules from regular staggered arrays
• Assembly of fibrils occurs outside of the cell from soluble precursor procollagens

Question 10

How are collagen fibrils strengthened?

Answer 10

-Covalent cross-links between side chains of lysine and hydroxylsine residues help to strengthen fibrils

Question 11

In collagen that do not form fibrils, how are collagen fibers linked?

Answer 11

-fibril-associated collagens bind to collagen fibrils and link them to one another and to other matrix compounds

Question 12

What kind of collagen is found in basal laminae?

Answer 12

• network-forming collagens

- types IV, VI, XVIII

Question 13

How is the structure of Type IV collagen different than normal?

Answer 13

• Gly-X-Y repeats are interrupted by short nonhelical sequences, making them more flexible.
• they form 2D cross-linked networks instead of fibrils

Question 14

What are Glycosaminoglycans? What is their structure?

Answer 14

• GAGs
  a) polysaccharides that from extracellular matrix gels
  b) have repeating units of disaccharides
  c) all sugars are modified with a sulfate group except for Hyaluron

Question 15

Hyaluronan

Answer 15

• the only GAG that is a single long polysaccharide chain.

- synthesized at the plasma membrane by a transmembrane hyaluronan synthase.