Chapter 11

Question 1

What is the extracellular matrix?

What are the two forms of this in animal and plant cells?

Answer 1

Most cells are embedded with an array of extracellular macromolecules that form different types of structure

Key in organization of cells in tissues of multicellular plants
Fills spaces between cells and binds cells and tissues together

Cell walls in fungi, algae, plant cells
Extracellular matrix is animal cells

Question 2

What are the 5 tissue types?

Answer 2

Epithelial tissue- extracellular matrix known as basal lamina underlies epithelial cells
Muscle tissue- surrounded by thing basal lamina
Adipose tissue- surrounded by thin basal lamina
Nerve tissue- surround by thin basal lamina
Connective tissue- bone tendon cartilage and loose connective tissue underlying skin
Slide 5-7

Question 3

What is the common extracellular matrices organization? (2 types of proteins)

Answer 3

Composed of tough fibrous structural proteins embedded in gel like polysaccharide material known as ground substance
Specialized adhesion proteins anchor cells to the extracellular matrix

Question 4

What is collagen?

What are the 5 main collagen classes?

Answer 4

Major structural protein of most the ECM
The single most abundant protein in animal tissues
Contain atleast 27 different members

1. Fibril-forming- fibres in connective tissue
2. Network forming- form basil lamina
3. Fibril associated- association of collagen fibrils
4. Anchoring- attachment of basal lamina
5. Transmembrane- cell surface molecules

Question 5

What is the structure of collagen?

Answer 5

Repeating amino acid primary sequence of collagens is a triple repeat of Gly-X-Y (x is usually proline, y is usually hydroxyproline)

Form triple helicies, 3 polypeptide chains wounds around eachother
Triple helicies line up in a staggered arrangement and are cross linked to form fibrils
Slide 12-14

Question 6

What are elastic fibers and elastin?

Answer 6

Elastic fibers- found in connective tissues, are particularly abundant in organs that regularly stretch and then return to original shape
Elastin- protein of elastic fibers, cross-linked into a network by covalent bonds formed between the side chains of lysine residues

Question 7

What are glycosaminoglycans (GAG)?

Answer 7

Gel forming polysaccharides of ECM that contain repeating disaccharides
Negative charge binds positively charged ions attracting and trapping water molecules and creating hydrated gel-like structure
GAGS covalently linked to specific proteins to form higher order structures known as proteoglycans
Disaccharides are sulfated which allows attraction and holding of water

Question 8

What are the three steps in higher order organization of matrix polysaccharides?

Answer 8

1. Glycosaminoglycans (GAGs)
2. Proteoglycans ex: aggrecan
3. Larger proteoglycan aggregates- number of proteoglycans interact with hyaluronan chains to form large complexes in ECM
   slide 20

Question 9

What are matrix adhesion proteins?

What is the principal adhesion protein?

Answer 9

Matrix adhesion proteins are responsible for linking the components of the matrix to one another and to the surface of cells
Fibronectin is the principal adhesion protein of connective tissues where laminin is the principal adhesion protein of the basal lamina

Slide 22

Question 10

What are the 4 binding domains of fibronectin?

Answer 10

Proteoglycan binding
Integrin binding 
Collagen binding
Proteoglycan binding
Slide 22

Question 11

What is nidogen in laminin?

Answer 11

Protein that links laminin to collagen type IV Agrin-large proteoglycan of ECM
slide 23

Question 12

What are integrins in cell-matrix interactions

Answer 12

Major cell surface proteins (integral plasma membrane proteins) that attach cells to extracellular matrix and are anchors for cytoskeleton in cell
THEY PROVIDE LINKAGE BETWEEN CYTOSKELETON INTRACELLULARLY AND THE EXTRACELLULAR MATRIX
they also serve as receptors that activate intracellular signalling pathways

Question 13

What is the structure of integrins?

Answer 13

Consists of dimers of one alpha and one beta subunit
Outer receptor (matrix binding) and inner regions (cytoskeletal binding)
Slide 26

Question 14

What are the two types of cell-matrix interactions involving integrins?

Answer 14

1. Focal adhesions- a type of cell-matrix junction that attaches a variety of cells to ECM (link actin filaments of cytoskeleton)
2. Hemidesmosomes- mediate epithelial cell attachments at which a specific integrins interacts with laminin in basal lamina (link intermediate filaments of cytoskeleton)
   STRONGEST cell-matrix junction
   Slide 28

Question 15

What are the 3 types of cell-cell junctions?

Answer 15

1. Stable adhesion junctions- adherens junction and desmosome
   Strongest cell-cell junction
2. Tight junctions- seals cells
3. Gap junctions

Question 16

What are adherens junctions?

Answer 16

Family of integral plasma membrane proteins in adjacent cells known as cadherins
Cadherins link to the actin cytoskeleton intecellularly and with eachother extracellularly

Cadherins links actin cytoskeleton of adjacent cells by these cell junctions
Slide 31

Question 17

What is desmosomes?

Answer 17

Involve a family of cadherins known as desmoglein and desmocollin that link the cytoskeletons of adjacent cells via these cell junctions
Slide 32

Question 18

What are tight junctions?

Answer 18

Important to function of epithelial cell sheets such as intestinal epithelial cells
Barrier between fluid compartments (ensure any molecules moving across the epithelial cel later in either direction must move through cell)
Separate apical and basal domains of plasma membrane which prevent lateral movement of integral membrane proteins between domains of cell
Slide 34

Question 19

Why do tight junctions always exist as part of a junctional complex (region of cell-cell contact containing a tight junction, an adherens junction, and a desmosome)?

Answer 19

Tight junction have minimal adhesive strength

Question 20

What are gap junctions?

Answer 20

Cell to cell communication and coordination of cell activity
Open channels through the plasma membrane that provide direct connections between cytosplam of adjacent cells
Allow for open flow of ions and other small molecules
Slide 37-38

Question 21

What is a connexin and connexon in gap junctions?

Answer 21

Connexin- member of family of transmembrane proteins that form gap junctions
Connexon- cylinder formed by six connexins in plasma membrane
Slide 37