BC18 Cell Junctions and ECM

Question 1

Filament Network Epithelium

Answer 1

actinL cell periphery, cell to cell contact, signaling, attach to basil lamina, cellular shape

Intermediate filaments: cytoplasm, cells to eachotehr and basil lamina, mechanical strength

Microtubules, trafficking

Question 2

cell to cell adhesions

Answer 2

Adhering Junctions: actin cytoskeleton

DesmosomesL IF of adjacent epithelia

Question 3

Adhering Junctions

Answer 3

Cadherin Junctions (Ecadherin)

• can bind across extracellular space
• Calcium plays key roll in binding

Cytoplasmic

• bound via proteins to actin filaments (adhesion belt)
• maintains structure

Question 4

Desmosomes

Answer 4

Protein components:

• transmembrane desmosomal cadherins
• desmoglein desmocollin
• bind across extra cellular space

Cytoplasmic: bound to IF by Keratin

• structural stability
• withstand tearing or shearing force

Question 5

Tight and Gap Jnxs

Answer 5

T Jxns
Transmembrane that bind to adjacent cells
-claudin/occludin
-maintain polarity (apical,BM)
-control paracellular (Na)
-regulated permeability for amino acids and monosaccharides from lumen

Gap Jxns:

• reversible change in conformation
• high cytosolic Ca levels or decreased cytosolic pH (damaged/sick) close Gap Jxns
• isolate damaged cell
• CONNEXONS
• regulated for neurons

Question 6

BM adhesions

Answer 6

focal adhesions. anchor epithelial cells via actin filaments to basil lamina. integrin dimers link to actin via collagen or liminin depending on integrin pair

hemidesmosomes: IF to BL (DO NOT CONTAIN desmocollin or desmoglein. Integrin dimers mediate attachment of keratin to IF within cell to the ECM laminin

both comprised of integrins, consisting of a alpha and beta dimer (link to ECM)

Question 7

BL

Answer 7

tough, flexible sheet of fibrous protiens

components produced by epithelia and fibroblasts,

anchor

Glycoprotiens: (main ones of BL)

• Laminin: large flexible, three interwoven pp chains, diS bonds, head groups can bind to eachother or collagen
• Type IV collagen: non fibriallar, three protein strans loosely packed, bind to one another orlaminin, forming mesh

ORGANIZED MESH

Question 8

Fibronectin

Answer 8

insoluble, component of BL

role in epithelial cell adherence.

-V shaped consisting of two polypeptides linked by diS molecules, each arm of V shape has binding domains for integrin, collagen fibers, and PG’s.
aka adaptor molecule

cal also be fibers on the outer surface of cells

Question 9

ECM

Answer 9

sparce distribution of fibroblasts.

mechanical strength and compressive resistiance via fibrous proteins (collagen, elastin, GP’s)

Question 10

Collagen Fibrils of ECM

Answer 10

Type I and Type II collagen in ECM

cross linked and higher order for more strength

Question 11

Collagen Formation

Answer 11

1. alpha chains synth as pro alpha chain splooled into lumen of EF
2. PTM: hydroxylation of AA Proline and Lysine (vitamin C ascorbic acid required) (prolyl/lysyl hydroxylase)
   3 PTM: glycosylation of hydroxylysine residues
3. three pro alpha chains self assemple
4. becomes procollagen triple helix
5. procollagen secreted to ECM
6. loose ends of each PP strand are cleaved (lysyl oxidase-catylizes oxidative deamination between lysine or hydroxylysine forming inter and intramolecular crosslinks)) forming mature collagen (tropocollagen)
7. tropocollagen self assemble into staggered array (Fibril), then higher order (fibers)

tropocollagen 1000 fold more hydrophobic than procollagen (self assembly)

also ensures they wont self assemble until out of the cell

• repeating glycines prolines and hydroxyproline create kinds that make up tropocollagen, enables interlocking
• covalent bonds between hydroxylysine very stable

Question 12

scurvy

Answer 12

vit C deficiency

decrease in amount of proline lysine hydroxylation on collagen fibers

unstable tropocollagen

collagen made often in periodontal ligaments and gingiva hence bleeding of gums and loose teeth

Question 13

Elastin

Answer 13

tensile stretchy strength recoil
lungs skin blood vessels

hydrophobic monomers extensively crosslinked

crosslinks act as molecular springs

Question 14

ground substance

Answer 14

carb rich molecules that form extensively hydrated gel like matric.

PG’s Hyaluronan, GP’s

PG’s made of glycosaminoglycans bound to core proteins

Question 15

GAGS

Answer 15

polysaccharide chains with amino sugar linked to acidic sugars

1. hyaluronan: hyaluronate-very long, not covalently bound to proteins, acts as scaffold. Neg charge, sot sulfated
2. Chondroitin sulfate and dermatan sulfate
3. Heparan sulfate (one of the gags attached to hyaluronan)
4. Keratan sulfate

2,3,4 short polysacc chains sulfated and covalently bound to protein + GAG+ PG

highly NEG charge, attract Na and water follows

FIll most EC space ONLY because of all the H2O they attract

Question 16

proteoglycans

Answer 16

with exception of hyaluronan most GAGs connected to a linear ‘core’ protein to form PG’s

serine residues of core protein are fist attached to a trisaccharide inker that then attaches to the rest of the GAG chain with multiple disacc repeats

pcs then attach to hyaluronan