MCM 2-10: Tissue Organization, Cell Junctions, and Extracellular Matrix Flashcards Preview

MSI Unit II > MCM 2-10: Tissue Organization, Cell Junctions, and Extracellular Matrix > Flashcards

Flashcards in MCM 2-10: Tissue Organization, Cell Junctions, and Extracellular Matrix Deck (36)
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General organization and function of major tissue types

Cellular - tissue composed mainly of cells. integrity and properties are derived from cell junctions (epithelium)

Connective - tissue composed mainly of ECM with a few cells that synthesize, remodel, and bind the ECM. Physical properties of tissue is provided by organization of ECM (loose CT, cartilage, bone, tendon)


what are anchoring/adhering junctions?

junctions whose primary purpose is to maintain tissue integrity under mechanical stress.

can be cell-cell or Cell-ECM junctions


Three components of anchoring/adhering junctions

transmembrane glycoprotein - anchoring portion

complex of linker proteins on cytosolic face - regulates assembly and connects to cytoskeleton

cytoskeleton - connection can be to intermediate filaments or microfilaments (actin). Distributes force due to mechanical stress over a large area, allow the glycoprotein to stay attached.


Four types of anchoring junctions

1. adherens junctions/zonula adherens

2. Focal Adhesions/Focal Contacts -

3. Desmosomes -

4. hemidesmosomes


Tight Junctions/Zona Occludes (5 features)

1. provide permeability layer across epithelial sheets like in small intestine - This allows regulated transport of nutrients through the cells (Transcellular transport). Na+2 dependant uptake occurs at apical membranes, faciliatated diffusion occurs at basolateral membranes
2. maintain cell polarity by keeping membrane trasnport proteins in correct locations

3. claudin and occludin are major proteins of tight juncctions
4. strings of transmembrane proteins interact with each other on adjacent cells via homophilic interactions

5. cytoskeleton not needed for integrity


Gap Junctions ( 3 features)

1. Provide means of communication between neighboring cells (such as electrical conduction in cardiac cells). Also known for passage of small molecules such as amino acids and vitamins

2. made of single protein called connexin. six connexin molecules associate in PM to form connexon (hemi channel). connexons on adjacent cells associate to form gap junctions

3. regulated by intracellular Ca+2 concentration or pH

high Ca+2 or low pH = gap junction close
low ca+2 or high pH = gap junction opens


three major families of extracellular matrix proteins

fibrous proteins, bulky space filling proteins, cross linking proteins


fibrous proteins

describe each type.

includes collagens (fibrillar, and type IV) and elastin

Fibrillar collagen provide tensil strength; resist stretching.
the pro-collagen triple helix is secreted from golgi and collagenases cleave the pro-peptides forming true collagen helices which then self associate into fibrils and fibers like tendons.

type IV collagen does not follow same pathway - when excreted into ECM it is not acted upon by collagenases, it forms mesh which is compoenet of basal lamina

Elastin provides elasticitiy. undergoes extensive cross linking following secretion via coalent linking of serine residues. elastic character is derived mostly from the many random coils in the polypeptide chain due to high proline content. The Glycoprotein fibrillin forms a sheath around the elastin fibers, preventing overstretching.


bulky space filling proteins

includes what?

does what?

including proteoglycans.

Resist compression forces and allow for rapid diffusion of soluble molecule like growth factors.

also permit cell migration

the GAGS on proteoglycans have many sulfate and carboxyl groups, giving them negative charges making them hydrophilic. they can bind noncovalently many water molecules

a hydrated gel is only 10% proteoglycan.

Using linker proteins, proteoglycans can complex with hyalauronic acid and resist compression forces

in loose CT, primary role of proteoglycan molecules is structure and space filling, permitting free movement of water soluble molecules as well as cells in the matrix


cross linking proteins

includes fibronectin and laminin.

Fibronectin - heterodimer that can assemble higher order structures. Many alternative-splice variants have modified functions. They have multiple binding sites giving them their functionality as crosslinking molecules. Fibronectin can bind :integrins, heparin, syndecan, types I,2,3 collagen, and fibrin

Laminin - a three chain polypeptide, forms component of basal lamina along with type 4 collagen and proteoglycan.
Laminin binds integrins on cell surface, heparin, TYPE 4 COLLAGEN


Anchoring junction diseases

result in loss of tissue binding and blistering, can be fatal
-pemphigus - autoimmune, antibodies generated against cadherins, disrupt cell-cell junctiojns

-epidermylosis bullosa simplex - defect in keratin assembly


Extracellular matrix protein diseases

ehlers-danlos - various fibirllar collagen defects, hyperextensible skin and joints

marfan syndrom - mutation in fibrillin gene, makes aorta prone to rupture

DMD - basal lamina plays role, as it surrounds and supports muscle cells


adherens junctions/zonula adherens

-cell-cell anchoring junctions
-transmembrane glycoproteins are cadherins which require Ca+2 to interact with another cadherin on adjacent cell (homophilic).
-linker proteins interact with actin filaments


Focal Contacts

-cell to ECM anchoring junctions
-TM glycoproteins are integrins (formed from alpha-beta subunit heterodimer) require Ca+2 to interact with fibronectin in the ECM (heterophilic)
-linker proteins interact with actin filaments



Cell:Cell anchoring junctions
-tm glycoproetins are caherins (like adherins junctions)
-linker proteins interact with IF like keratins
-they connect IF filaments across epithelial sheet



cell:ECM anchoring junctions
-TM glycoproteins are integrin a6/b4 - attatch the of basal lamina
-linker proteins interact with IF
-connect intermediate filaments across an epithelial sheet


The two Cell:Cell Adhering/anchoring junctions and what they have in common

Adherens junctions and Desmosomes
-cadherin glycoprotein
-homophilic interaction (cell to cell)

cell:cell are homophilic interactions with cadherin glycoproteins


The two cell:ECM adhering/anchoring junctions and common features

Focal adhesions and Hemidesmosomes
-integrin glycoprotein
-heterophilic (cell:ECM)

Cell:ECM are heterophilic interactions with integrin glycoproteins


the cytoskeleton of the 4 anchoring junctions

Adherens and Focal = Actin

Desmosomes and Hemidesmosomes - Intermediate filaments


what do adherens junctions do?

provide strength and are important in development


what do focal adhesions do?

orient contracts, important in developmental processes


what do desmosomes do?

maintain cellular tissue integrity


what do hemidesmosomes do?

maintain cellular tissue integrity


describe the ECM

major component of CT, giving CT strength and integrity
-generated by fibroblasts, Chondroblasts(cartilage) or osteoblasts (bone)


three major families of ECM proteins

fibrous proteins, bulky space filling proteins, cross-linking proteins



a glycoprotein which surrounds the fibrous protein elastin to prevent overstretching


the crosslinking proteins fibronectin and laminin bind what?

fibronectin bind integrins (focal adhesions and desmosomes), heparin (GAG), syndecan (proteoglycan), 1/2/3 collagen, fibrin (blood clotting)

laminin - integrins on cell surface, heparin (GAG), type 4 collagen



disease type?

Anchoring Junction Disease - An autoimmune disease in which antibodies are generated against cadherins, disrupting cell-cell junctions leading to a loss of tissue integrity/blistering


Epidermolysis Bullosa Simplex –
disease type?

Defect in keratin assembly. anchoring junction disease


Ehlers-Danlos syndrome

disease type?

– Various fibrillar collagen defects. Causes hyper extensible skin and joints.
– Mutation in the fibrillin gene. Makes the aorta prone to rupture.

ECM protein disease

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