Cell Junction, Cell adhesions & Extracellular Matrix (Sept. 9-Denning) Flashcards by Andrew Taniguchi

List the 2 main types of tissue involved in cell junctions

1) Epithelial tissue

2) Connective tissue

How well did you know this?

Not at all

Perfectly

What are the characteristics of epithelial tissue

Low ECM & High # cells
Cells are tightly bound together in sheets
Cells bear most of the mechanical stress through junctional complexes that attach to the cytoskeleton.

How well did you know this?

Not at all

Perfectly

List the characteristics of connective tissue

High ECM & Low # of cells
Matrix is rich in fibrous polymers (e.g., collagen)
Matrix bears most mechanical stress

How well did you know this?

Not at all

Perfectly

List the 5 main types of cellular junctions and their particular functions

1) Occluding: Seal cells so nothing can pass in between (tight junctions)
2) Cell-Cell Anchoring: Connects lateral walls of cells together (Actin & Adherens/IFs & desmosomes)
3) Channel-Forming: Allows selective transport of materials between cells (gap junctions)
4) Cell-Matrix Anchoring: Links together cell and ECM (actin/focal adhesions or hemidesmosomes/IFs)
5) Signal-Relaying junctions: Neurotransmitter secretions

How well did you know this?

Not at all

Perfectly

Describe the function of claudins and occludins in tight junctions

Claudins are 4-pass transmembrane proteins.
Found at lateral surface just below apical surface of cell.
Prevent paracellular transport
Occludins serve similar function, but are found in significantly less number

How well did you know this?

Not at all

Perfectly

T/F: Glucose can normally pass between epithelial cells of the intestine

False: tight junctions prevent leaking and transportation of molecules between cells. Glucose uses Na+ symporter to move and undergo transcellular transport

How well did you know this?

Not at all

Perfectly

What is the function of anchoring junctions?

Stabilize cells against mechanical stress

- Mechanically attach cells and their cytoskeleton to their neighbors or to the extracellular matrix

How well did you know this?

Not at all

Perfectly

For the 4 subtypes of anchoring proteins, list the (1) type, (2) transmembrane adhesion protein, (3) cytoskeletal attachments

1) Adherens (cell-cell) - cadherin - actin
2) Desmosome (Cell-cell) - cadherin (desmoglein) - IF
3) Focal adhesions (Cell-matrix) - integrin - actin
4) hemidesmosomes (cell-matrix) - integrin - IF

How well did you know this?

Not at all

Perfectly

What is the function of cadherin?

Cadherins are transmembrane adhesion proteins that work to form cell-cell junctions between filaments via anchor proteins

How well did you know this?

Not at all

Perfectly

What is the adhesion belt in adherens junctions?

Join an actin bundle in one cell to actin bundle in adjacent cell
Form adhesive belt just below tight junction

How well did you know this?

Not at all

Perfectly

What ion does cadherin require for assembly?

Ca2+

How well did you know this?

Not at all

Perfectly

Where are desmosomes typically found?

Between cells. They function as “spot welds”

They are anchored to IFs via desmosomal cadherins and plaque proteins

How well did you know this?

Not at all

Perfectly

What are the functions of focal adhesions?

Link the cell to ECM

- Allows cell to hang on to surroundings (think leucocyte rolling)

How well did you know this?

Not at all

Perfectly

Focal adhesions bind to \_\_\_\_ via the transmembrane protein \_\_\_\_\_\_
(A) actin; integrin
(B) microtubules; integrin
(C) intermediate filaments; cadherin
(D) desmosomes; actin

(A) Focal adhesions are connected to actin via anchoring proteins and use integrins (transmembrane ECM binding proteins) as the interacting subunits

How well did you know this?

Not at all

Perfectly

List the (1) function, (2) transmembrane protein that mediates the connection, and (3) the final end connection of hemidesmosomes

1) Distribute forces on an epithelium to the basal lamina
2) Integrins mediate basal lamina adhesion
3) Anchor proteins link integrins to intermediate filaments

How well did you know this?

Not at all

Perfectly

Describe the phenomenon that is cadherin dependent sorting?

Homophilic binding of cadherin dimers favors association of like cadherin dimers. This binding allows the eventual separation and distinct cell types aggregating together which allow tissue homeostasis and sorting of similar cell types

How well did you know this?

Not at all

Perfectly

What are selectins?

Selectins are Lectins: Carbohydrate binding proteins
They are transient, calcium-dependent adhesion molecules
which exhibit heterophilic binding and are connected to integrins

How well did you know this?

Not at all

Perfectly

Elaborate on the phenomenon that is leukocyte rolling in the bloodstream following an injury. What are the functions of selectins and integrins in this interaction?

Injury causes release of cytokines…Cytokines cause surface proteins to display selectins cause carbohydrates to stick (typically found on surface of WBC)
Transient low affinity, low strength with SELECTINS to WBC
Integrins cause a stronger adhesion when finally recognized and allow import of WBC into cell through endothelium.

What are communicating gap junctions?

Electrically couple adjacent cells and small molecules such as ions, and nucleotides can pass through.
Important for heart muscles to allow things like Ca2+ to move through and equilibrate the spike throughout all cells to give unified contraction.
Cells that are diferent from each other (not specialized cells will not be coupled)

Describe the structure of connexins and how they relate to the formation of gap junctions

Gap junctions are formed by connexins :
-4 pass transmembrane proteins
-6 connexins form a functional pore: Connexon
-Permeability varies with connexin composition
�

Discuss the function of scaffold proteins in synaptic junctions

Scaffold proteins organize adhesive proteins, ion channels, receptors and other vesicle-docking proteins to relay signals across a synapse (neurons).

The ECM is a hydrated gelatinous material that is made up of these 3 components…

Glycosaminoglycans, proteoglycans, and fibrous proteins.

Cells which secrete ECM include…

List 4

1) Fibroblasts
2) Chondroblasts (cartilage)
3) Osteoblasts (bone)
4) Epithelium (basal lamina)

What type of tissue is ECM prevalent in?

Connective tissue

1) This tissue type uses matrix to bear mechanical stress... | 2) This tissue type absorbs mechanical stress through cellular junctional complexes that attach to the cytoskeleton

1) Connective tissue | 2) Epithelial tissue

Describe 3 characteristics of Glycosaminoglycans (GAGs)

1. One sugar is an amino sugar (Sulfated and bears (-) charge) 2. Other sugar is a ironic acid (glucoronic or iduronic...Coo- group) 3. polysaccharides are stiff and absorb large amounts of water: occupy space

Hyaluronan (hyaulorinic acid or hyaluronate): (A) contains sulfated sugars (B) is composed of complex GAG consisting of more than 25,000 disaccharide units (C) not attached to protein and is synthesized at plasma membrane (D) Is not resistant to compressive forces in joints and tissues (E) Both A and D

(C) Hyaluronan is simplest GAG of up to 25,000 disaccharide units. It is a space filler through which cells migrate in ECM and resists compressive forces

How are proteoglycans different from glycosaminoglycans? | Do they differ from glycoproteins?

Proteoglycans are composed of a core protein to which GAG is covalently attached. Unlike glycoproteins, proteoglycans are highly carbohydrate like in composition (95% by weight) and contain at least 1 GAG

What is the difference between glycoproteins and proteoglycans?

Glycoproteins have short, branched side chains and are mostly protein in composition; while proteoglycans usually contain long unbranched side chains and are mostly carbohydrate in composition.

What are the functions of proteoglycans?

1. regulation of molecular and cellular movement (gels) | 2. chemical signaling between cells - binding of growth factors, protease...

What are the main characteristics of collagens protein in ECM

1. Long, stiff triple alpha helix 2. Gly - proline - hydroxyproline repeating sequences 3. Hydroxyproline and hydroxylysine form interchain H-bonds...stabilize triple helix 4. Highly cross link through lysine aldehydes 5. primarily responsible for strength of ECM

What are the two genetic collagen disorders we have discussed in class?

1. osteogenesis imperfecta: Type I collagen defect with autosomal dominant inheritance. Leads to increased bone fractures and skeletal abnormalities 2. Ehlers-Danlos syndrome: Mutations in Type I, II, V collagen. decreased collagen hydroxylation. Autosomal dominant inheritance. Leads to skin hyper-extensibility, joint dislocation, hyper mobility, vessel weakness

What is the function of elastin?

Imparts elasticity and flexibility to tissues

Marfan's syndrome is a mutation in the fibrillin sheath of elastic fibers. It is autosomal dominant disease characterized by which one or more of the following symptoms: a) excessive growth of long bones b) short stature c) normal cartilage and ligaments d) weakened blood vessels, hear valves

Both (a) and (d) | Alos causes: Aortic dilation/rupture, tall stature, weakened blood vessels, malformed cartilage and ligaments

What is the function of fibronectin?

Adhesive glycoprotein that binds cells to matrix and guides cell migration

Fibronectin binds to (1) ______ to attach to the ECM. It does this via a triplet amino acid (2) ______ interaction

(1) integrins | 2) RGD (Arg-Gly-Asp

List the 5 main functions of the basal lamina

1. molecular filter 2. barrier for cell migration & 3. cell migration 4. cell orientation 5. cell survival

What are the 2 main components of the basal lamina

1. Laminin - adhesive protein that binds cells to the basal lamina 2. Type IV collagen

True/False: The basal lamina allows for regeneration of nerves and acetylcholine receptors at the site of original junction in degenerated muscle and nerve experiments

True. Basal lamina allows proper orientation and regeneration as long as residual shell of residual basal lamina is left intact

Describe the main characteristics of integrins (list of 5)

1. heterodimer of alpha and beta glycoproteins 2. overlapping specificity - multiple integrins can bind fibronectin or laminin (ECM matrix proteins) 3. Linked to actin cytoskeleton 4. Matrix receptors 5. Low affinity, high copy number

What are the two adaptor proteins that are used to anchor integrins with actin filaments?

Vinculin and talin

Describe inside-out signaling regulation of integrins

- Inactive integrins are activated by the cells - Strong talin binding - Bind antigen presenting cell pr can cause aggregation

Descibe outside-in signaling regulation of integrins

- clustering of integrins at ECM contact sites activates signaling - characterized by strong ligand binding on outside of cell - focal adhesion kinase (FAK) is recruited and activated - Similar to conventional GF receptors