The Extracellular Matrix of Animal Cells

Question 1

form of extracellular matrix in animal cells?

Answer 1

in animal cells, the ECM takes on a variety of forms in the different tissues

Question 2

three types of ECM are?

Answer 2

1. Bone-rigid ECM that contains a small number of interspersed cells
2. Cartilage- mostly of matrix materials more flexible than bone
3. Connective tissue-relatively gelatinous and contains interspersed fibroblast cells

Question 3

Despite the diversity of function, the ECM consists of the same three classes of molecules, what are they?

Answer 3

1. structural proteins such as collagens and elastins, which provide strength and flexibility
2. protein-polysaccharide complexes, proteoglycans, that provide the matrix
3. adhesive glycoproteins, - fibronectins and lamins, that allow cells to attach to the matrix

Question 4

Despite the diversity of function, the ECM consists of the same three classes of molecules: Structural proteins
what do they do?
how abundant are they?

Answer 4

• structural proteins provide strength and flexibility

- the most abundant ECM component in animals is a family of closely related collagens

Question 5

Despite the diversity of function, the ECM consists of the same three classes of molecules: Structural proteins 
Collagens
-what do they do?
-how are they formed? 
-structure?
-amino acid composition?

Answer 5

• form fibers with high tensile strength
• collagen is secreted by several types of cells in connective tissue including fibroblasts
• occur as a rigid triple helix of intertwined polypeptides
• have an unusual amino acid composition- very high in glycine and the rare amino acids hydroxylysine and hydroxyproline

Question 6

Despite the diversity of function, the ECM consists of the same three classes of molecules: Structural proteins
Collagen fibers
-how are they visible
- composition and strength?
-structure of collagen fibers in ER?
-how is the stability of collagen fibrils reinforced?

Answer 6

• visible in the ECM under scanning EM
• fibers are enormously strong, and are composed of numerous fibrils
• 3 a-chains assemble to form a triple helix (procollagen with nonhelical ends) are secreted and cleaved (loose ends) by procollagen peptidase which induces the spontaneous formation of fibrils and fibers
• the stability of collagen fibrils is reinforced by hydrogen bonds (form crosslinks within and between collagen molecules) involving hydroxylysine and hydroxyproline

Question 7

Despite the diversity of function, the ECM consists of the same three classes of molecules: Structural proteins

• how is elasticity provided to the ECM?
• compositon of elastins?
• how do elastins work?

Answer 7

• elasticity provided to the ECM by stretchable elastic fibers principally composed of elastins
• elastins are rich in glycine and proline, and the elastin molecules are crosslinked by bonds between lysine residues.
• tension causes network to stretch and release of tension causes individual molecules to relax

Question 8

Despite the diversity of function, the ECM consists of the same three classes of molecules: Structural proteins
collagen and elastins:
-how are elastins different from collagen?
-the collagen and elastin fibers are both enmeshed in?

Answer 8

• proline resiudes in elastins are not hydroxylated and no hydroxylysine is present
• the collagen and elastin fibers are enmeshed in a gel-like network of proteoglycans, glycoproteins with a lot of glycosaminoglycans

Question 9

Despite the diversity of function, the ECM consists of the same three classes of molecules: Protein-polysaccharide complexes, proteoglycans that provide the matrix

glycosaminoglycans (GAGs)

• what are they?
• most common types?
• composition?

Answer 9

• large carbohydrates with repeating disaccharide units
• most common types are chondroitin sulfate, keretan sulfate, and hyaluronate
• disaccharide repeating unit has one amino sugar, either N-acetlyglycosamine (GlcNAc) or N-acetlygalactosamine (GalNAc)
• other sugar is usually a sugar or sugar acid, commonly galactose (Gal) or glucuronate (GlcUA), the amino sugar has one or more sulfate groups attached

Question 10

Despite the diversity of function, the ECM consists of the same three classes of molecules: Protein-polysaccharide complexes, proteoglycans that provide the matrix

• most glycosaminoglycans in the ECM are covalently bound to proteins to form?
• proteoglycans and GAGs?
• structure of proteoglycans?
• what are they?
• present as?
• cartilage and proteoglycans

Answer 10

• proteoglycans
• each proteoglycan has a number of GAG chains attached along the length of a core protein
• vary greatly in size depending on the size of the core protein and the length of the carbohydrate chains
• integral components of the plasma membrane with their core polypeptides embedded in the membrane
• present as individual molecule
• in cartilage, numerous proteoglycans become attached to long molecules of hyaluronate

Question 11

Despite the diversity of function, the ECM consists of the same three classes of molecules: Adhesive glycoproteins, fibronectins and lamins, that allow cells to attach to the matrix 
Fibronectins
-how many domains? to do what?
-how is this proteins produced? many varieties?
-subunits of fibronectin? 
-several domains bind what?
-other domains bind? how?
-migraory cells grown on fibronectin? 
-blood plasma and fibornectin?

Answer 11

• have multiple domains, to bind molecules in the ECM and receptors on membranes
• RNA transcribed from the fibronectin gene is processed to produce many different mRNAs/many different variants of this protein
• has two large subunits linked near to C-terminals by two disulfide bonds
• several domains bind one or more ECM macromolecules (collagen, heparin, fibrin)
• other domains recognize and bind cell surface receptors via the RGD (arg-gly-asp) sequence
• when migratory cells are grown on fibronectin, they adhere to it
• blood plasma fibronectin promotes blood clotting (has domains for binding fibrin and attaches platelets to form clots)

Question 12

Despite the diversity of function, the ECM consists of the same three classes of molecules: Protein-polysaccharide complexes, proteoglycans that provide the matrix 
Laminins 
-where are they found?
-composition? 
-structure? 
-consist of several domains including..
-what does its binding do?

Answer 12

• laminins are found mainly on the basal lamina
• laminins consist of three long polypeptides, a, B, and y which combine to form many types of laminin
• disulfide bonds hold the polypeptides together in the shape of a cross, with part of the long arm wound into a three stranded coil
• like fibronectin, laminins consists of several domains including binding site for type IV collagen, heparin, heparin sulfate, and enactin, and receptors on cell surfaces
• its binding sites allow laminin to serve as a bridging molecule that attaches cells to the basal lamina

Question 13

Basal lamina and laminins

• what is the basal lamina?
• where is it located?
• what does the basal lamina do?
• what do all forms of basal lamina contain?
• what can the cells of basal lamina do?
• most abundant glycoprotein in basal lamina?

Answer 13

• a thin sheet of specialized extracellular material
• underlies epithelial cells thereby separating them from connective tissues
• basal lamina also surround muscle cells, fat cells, and schwann cells
• basal lamina serves as a structural support and a permeability barrier
• the basal lamina beneath epilthelial cells prevents the passage of underlying connective tissue cells into the epithelium but permits the migration of the WBC needed to fight infections
• all forms of basal lamina contains type IV collagen, proteoglycans, laminins, and another type of glycoprotein enactin or nidogen
• cells can alter their properties of their basal lamina by secreting enzymes that catalyze changes in the lamina that degrade the ECM locally, allowing cells to pass through,
• laminins are most abundant glycoproteins in basal lamina