The Extracellular Matrix of Animal Cells

Question 1

What are the three types of ECM?

Describe them.

Answer 1

Bone - consists largely of a rigid extra cellular matrix that contains a tiny number of interspersed cells

Cartilage - tissue constructed almost entirely of matrix materials, but more flexible than bone

Connective Tissue - surrounding glands and blood vessels has a relatively gelatinous extracellular matrix containing numerous interspersed fibroblast cells

Question 2

What are the three classes of molecules in the ECM?

Answer 2

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 3

1. Structural Proteins:

what is collagen?

how does it represent itself in the ECM?

Answer 3

collagen is the most abundant ECM component in animals, occur as a rigid triple helix of intertwined polypeptides

collagens form fibers with high tensile strength

Question 4

1. Structural Proteins

what is procollagen?

Answer 4

a precursor molecule that is converted to collagen by proteolytic cleavage of sequences at both the N- and C- terminus ends.

Question 5

1. Structural Proteins

what is an elastin?

how is an elastin used in the ECM?

Answer 5

a family of ECM proteins what provide elasticity to the ECM

elastin molecules are cross-linked to one another by covalent bonds between lysine residues

Question 6

2. Protein-polysaccharide

Glycosaminoglycans (GAGs)

what are they?

how do they make up the matrix?

Answer 6

large carbohydrates characterized by repeating disaccharide units

most are covalently bound to protein molecules to form proteoglycans

Question 7

2. Protein-polysaccharide

Proteoglycans

how do they make up the matrix?

Answer 7

proteoglycans are integral components of the plasma membrane, with their core polypeptides embedded within the membrane

proteoglycans can also by covalently linked to membrane phospholipids

Question 8

2. Protein polysaccharide

what is hyaluronate?

Answer 8

hyaluronate is a glycosaminoglycan found in high concentration in the extracellular matrix where cells are actively proliferating or migrating, and the joints between moveable bones

Question 9

3. Adhesive glycoproteins

what are fibronectins?

Answer 9

fibronectins are a family of closely related adhesive glycoproteins in the ECM and are widely distributed in vertebrates

fibronectin molecules consist of two very large polypeptide subunits that are linked near their carboxyl ends by a pair of disulfide bonds

Question 10

3. Adhesive glycproteins

what do fibronectin domains bind to?

Answer 10

domains bind to one or more specific kinds of macromolecules located in the ECM or on cell surfaces, including several types of collagen, heparin and the blood clotting protein fibrin

Question 11

3. Adhesive glcoproteins

what are laminins?

Answer 11

laminins are found mainly in the basal lamina

laminins consist of three long polypeptides alpha, beta and gamma combine to form many types of laminins

disulfide bonds hold the polypeptides together in the shape of a cross

Question 12

3. Adhesive glycoproteins

What are MMP’s (matrix metalloproteinases)?

Answer 12

enzymes which require metal ions as cofactors, degrade the ECM locally allowing cells to pass through the ECM (metastasizing cancer cells)

Question 13

3. Adhesive glycoproteins

what are integrins?

Answer 13

the recetors that are on the surface of plasma membranes where laminins and fibronectins can bind to

they INTEGRATE the cytoskeleton with the extracellular matrix

Question 14

3. Adhesive glycoproteins

what are focal adhesions?

Answer 14

migratory and non-epithelial cells attach to the ECM molecule through focal adhesions

the contain clustered integrins that interact with bundles of actin microfilaments via several linker proteins

Question 15

3. Adhesive glycoproteins

what are hemidesmosomes?

Answer 15

they are found in epithelial cells

a major type of integrin-mediated attatchment where in epithelial cells the hemidesmosomes attach to the laminin in the basal lamina

Question 16

3. adhesive glycoproteins

what is anchorage-dependent growth?

Answer 16

requirement that cells be attached to a solid surface such as ECM before they can grow and divide

Question 17

3. adhesive glycoproteins

what are costameres?

what is dystrophin?

Answer 17

an attachment structure at the surface of striated muscle

contain many of the same proteins found at focal contracts in addition to the protein dystrophin

dystrophin is a large protein that interacts with a complex that includes integral membrane protein dystroglycan and the sarcoglycan-sarcospan complexes

Question 18

3. adhesive proteoglycans

what is the glycocalyx?

what are the roles of the glycocalyx?

Answer 18

a carbohydrate rich zone that often surrounds the plasma membrane

• cell adhesion
• recognition
• protection of the surface
• creation of permeability barriers

Question 19

what do plant cell walls consist of?

Answer 19

mainly of long cellulose microfibrils enmeshed in a network of branched polysaccharides and glycoproteins called extensins

• cellulose
• hemicelluoses
• pectins
• extensins
• lignins

Question 20

cellulose in the cell wall:

what do they look like?

Answer 20

long, ribbonlike structures that are stabililzed by intramolecular hydrogen bonds

Question 21

hemicellulose in the cell wall:

what does it look like?

Answer 21

chemically and structurally distinct from cellulose

heterogeneous group of polysaccharides, each consisting of a long, linear chain of a single kind of sugar with short side chains bonded into a rigid network

Question 22

pectins in the cell wall:

what are pectins?

Answer 22

branched polysaccharides with backbones called rhamnogalacturonans; the side chains have the same monosaccharides found in the hemicellulose

Question 23

what are extensins?

Answer 23

group of related glycoproteins, which are deposited in soluble form

in the cell wall, extensins become covalently crosslinked to on another and cellulose

Question 24

what are lignins?

Answer 24

insoluble polymers of aromatic alcohols found mainly in woody tissues

localized between cellulose fibrils

Question 25

how are cell walls synthesized?

Answer 25

1. middle lamella
2. primary cell wall which is a loosely organized network of cellulose, hemicellulose, pectins, and glycoproteins

once cells have stopped growing they add a secondary cell wall

Question 26

what are plasmodesmata?

Answer 26

junctions between plant cells that allow for cell-cell communication and cytoplasmic continuity