EXTRACELLULAR MATRIX / CELL ADHESION / JUNCTIONS

Question 1

EXTRACELLULAR MATRIX

Answer 1

System of protein molecules and polysaccharides filling intercellular space especially in connective tissue
-PROTEINS = fibrous *fibrillin 1) and glycoproteins
-POLYSACCHARIDES = glycosaminoglycans (GAGs) and proteoglycans

FUNCTIONS: fills intracellular space, determines mechanical and other physical properties of tissues

Question 2

EXAMPLES OF ECM PROTEOGLYCANS AND GAGs

Answer 2

Hyaluronon
Perlecan
Decorin
Aggrecan

Question 3

EXAMPLES OF ECM FIBROUS PROTEINS

Answer 3

Type IV collagen
Fibrillar collagen

Question 4

EXAMPLES OF ECM GLYCOPROTEINS

Answer 4

Laminin
Fibronectin
Nidogen

Question 5

WHAT TYPES OF CELLS PRODUCE EXTRACELLULAR MATRIX?

Answer 5

Cells of connective tissue producing extracellular matrix:
* Fibroblasts (most of connective tissues)
* Chondroblasts (cartilage)
* Osteoblasts (bone)

Question 6

COLLAGENS

Answer 6

represents 25% of total protein mass of human body (most abundant protein)
-triple helices, fibrils, fibers (I, II, III)
-> very thick and strong
-contain minor hydroxyamino acids (hydroxylyserine, hydroxyproline)
-procollagen (prevents collagen from synthesizing into a fibril inside fibroblast) synthesised out of cell and shortened by collagenase to produce mature collagen which can self assemble orderly
(mutation in this enzyme = hyper extensible skin)

Question 7

ELASTIN

Answer 7

polymer of individual fibres
-elastic characteristic (normally are folded into each other, but can straighten and stretch) – ideal for the epithelium of arteries

Question 8

FIBRONECTIN

Answer 8

dimer binding to collagen
-functions to anchor to ECM collagen through junctions (desmosomes)
-if we have an in vitro culture, we cover the base with fibronectin → anchorage > when we want to remove the sediment → we use trypsin, so that fibronectin “lets go” of the cuvette

Question 9

LAMININ

Answer 9

trimer, found in basal lamina
-provide adjacent cells with a mechanical scaffold and biological information either directly by interacting with cell surface components, or indirectly by trapping growth factors

Question 10

GLYCOSAMINOGLYCAN (GAG)

Answer 10

non-branched polysaccharides formed by disaccharide units
-subunits = amino sugar + gluronic acid, often contain sulphate (SO3-)
-main types of GAG - hyaluronan (only one that doesn’t contain sulphate), chondroitin sulphate, dermatan sulphate, heparane
sulphate, keratane sulphate

Question 11

PROTEOGLYCAN

Answer 11

• long protein (skeleton), GAG bound to the sides
  -able to absorb large amounts of water
  -types of proteoglycans:
  decorin – common in connective tissue (small molecule)
  aggrecan – in cartilage (large molecule)
  perlecan – in basal lamina
  -proteoglycan aggregate – brush like structure, proteoglycans are attached to hyaluronic acid, most common are aggrecan aggregates

Question 12

OCCULUDING CELL JUNCTION

Answer 12

cells tightly packed, no water can pass through
-isolates the space between cells – responsible for the selectivity of the epithelium
→ nothing can pass in-between cells, everything must pass through them
-proteins include occludin and claudin
-ensures sealing strand in epithelium

Question 13

ANCHORING CELL JUNCTIONS

Answer 13

Cell to cell interaction and to ECM

bound to microfilaments:
ADHESIVE = ensure cell- cell connection
→ Via proteins cadherin
Forms adhesion belt (zonula adheres) around whole cell, which is found under the occluding junction
FOCAL = ensures cell- ECM connection
→Via proteins integrins

bound to intermediate:
DESMOSOMES = mediate connection of cell – cell
→ via protein cadherin and cytoplasmic plaque
–> attaches intermediate filaments inside the cell onto cytoplasmic membrane
HEMIDESMOSOMES = the connection of cell-ECM
→ via protein integrin
→ attachment to basal lamina

Question 14

CELL JUNCTION

Answer 14

communication of two cells through the connection of their cytoplasm

GAP JUNCTION = Nexus
→formed by protein connexin - 6 molecules of connexin forms hold the channel - connexon
->two connexons (each in one cell) tied to each other form a small channel connecting the two cytoplasm
-passage of molecules to <1000 Da/ 1kDa, larger do not pass
* small organic molecules pass, e.g. signal molecule

Question 15

TRANSIENT INTRACELLULAR ADHESION

Answer 15

form first temporary cell connections during and shortly after their origin
-> allow the formation of permanent junctions, help in sculpturing
-selectins are proteins on cell surface, bind saccharides and form temporary intercellular junctions in the blood stream

Question 16