Lectur 5: Interactions Between Cells Flashcards
What are tight junctions also called and what is its importance?
They are also called occuluding junctions, they help to seal neighborhouring cells together in an epithelial sheet to prevent leakage and helps to polarize the cell
What does adherens junction do in epithelial cell?
It joins an actin bundle in one cell to a similar bundle in a neighbouring cell.
What does desmosome do in epithelial cell?
It joins intermediate filaments in one cell to those in a neighbour
What does gap junction do in epithelial cells?
Forms channels that allow small, intracellular water soluble molecules including inorganic ions and metabolites to pass from cell to cell
What do hemodesmosome do in epithelial cell
They anchor intermediate filaments in a cell to the basil lamina
In what order are the junctions present in epithelial cells?
Tight junctions, adherens junctions, desmosomes, gap junctions, and hemidesosomes
Which three junctions help to hold the cells together ?
Tight junctions, adhere junctions and desmosome
What is an important characteristic about MATURE epithelial cell?
They are all polar
What forms the sealing strand?
Tight junctions
What are cell-cell anchoring junctions?
Adherens junction and desmosomes
What is a cell-ecm anchoring junction in epithelial cell?
Hemidesmosome
How many transmembrane proteins does the tight junctions have? And how do they interact
Claudia and occludin are the two transmembrane proteins in the epithelial cell’s tight junction. These are required in both cells and Claudia interacts with Claudia from the other cell and same with occludin.
Both the extracellular domains interact.
How do transmembrane adhesion proteins interact in an epithelial cell?
Extracellular domains interact with Adhesion proteins of neighboring cells or extracellular matrix
Intracellular cellular domains interact with linker proteins.
What is the role of intracellular linker proteins in an epithelial cell ?
These CYTOSOLIC PROTEINS link the adhesion proteins to the cytoskeletal filaments
What are the transmembrane adhesion proteins in Adheres junction?
Classical cadherins
What are the transmembrane adhesion proteins in desmosome
Non classical cadherins - desmoglein and desmocolin
What are the transmembrane adhesion proteins in hemidesmosome
aplha6beta4 intergrin
What extracellular binding does adherens junction bind to?
Classical cadherin on neighbouring cell
What extracellular binding does the desmosomes junction bind to?
Desmoglein and desmocollion on neighbouring cell
What extracellular binding does hemidesmosome junction bind to?
Extracellular matrix proteins
What do the adherens juntions encircle?
The inside of the plasma membrane
What are the transmembrane proteins in adherens juntions and what do they interact with and hwo are they linked to the actin filaments?
Cadherins, interat with cadherins from the neighbouring cells, and INTRACELLULAR linker proteins link cadherin proteins to actin filaments
To make a gap junction, how many connexons or intercellular channels are required?
2 connexons form one intercellular channel (at least one intercellular channel is required for gap junction)
to make one connexon you need 6 connexins.
What filaments provide the most structural strength?
Intermediate filaments
What do the desmosomes do and what are they linked to and connect to?
They are linked to keratin filaments and connect to neighbouring cell
What do plants cells lack and have
They lack the animal junctions and have cells wall that provides mechanical strength.
Plasmodesmata are the intercellular junctions which allow for communication between cells.
What do the gap junctions allow to pass?
It allows ions and metabolites and is not very selective as to what passes through. It allows cAMP, nucleotides, glucose, amino acid. But it doesn’t allow macromolecules, proteins and nucleic acids.
How do you close gap junctions?
Any extracellular or intracellular signals can close gap junctions:
Treatment with dopamine closes gap junctions
Dramatic increase in cytosilic Ca2+ closes the junction and prevents loss of metalolites from adjacent cells.
How is gating controlled in plant cell?
Enchanced callose deposition blocks movement of large complex molecules. Callose is a plant polysaccharide and permeability can be controlled through reversible callose deposition
What is the general format of cells and ECM
Epithelial cells, basil lamina and connective tissues
What are the difference between epithelial tissue and connective tissue
Epithelial tissue is in the intestinal lining, skin epidermis while connective tissue is in skin dermis, bone, tendon and cartilage
Cells are closely assoassociated in epithelial while cells are rarely connected in connective tissues
In epithelial cells, cells are attached to each other while in connective tissues cells are attached to the matrix
There is limited ECM in epithelial tissue (thin basil lamina) while plentiful in Connective tissue
Cytoskeleton filaments provide resistance to mechanical stress and ECM provides resistance to mechanical stress
What are the 3 major classes of macromolecules in extracellular matrix?
- Glycosaminoglycans and peoteoglycans
- Fibrous proteins (collagens, elastin)
- Glycoproteins (lamina, fibronectin)
What is the primary complement in connective tissues?
ECM
How do different tissues have different properties
It is the different compositions of ECM
What are the characteristics of GAGs (glucosaminoglycans)
They are long, linear, chains of a repeating disaccharides
They are highly negatively charged (attract Na+ and water)
Form hydrated gels, resist compression and are space filling
Most GAGs synthesized inside the cell and released by exocytosis
What is an example of Glycosaminoflycans
Hyaluronan it is a simple GAG, long chain of repeating disaccharide subunits
It is spun directly from cell surface by a plasma membrane enzyme complex
What are characteristics of proteoglycans
These are subclass of glycoproteins
These are proteins either attest one sugar side chain which must be a glycosaminoglycan (GAG)
More extensive addition of sugar (95% or total weight)
These are also secreted
What are the characteristics of collagen?
It is a fibrous protein which provides tensile strength and resist stretching
A typical collagen is a fibril-forming collagen.
Three chains wound around each other in a triple helix and assemble into ordered polymers to form collagen fibrils, these then pack together into collagen fibers
What secretes the collagen protein?
It is secreted as procollagen by fibroblasts (skin, tendons, other connective tissue) and osteoblasts (bones) once the procollagen is secreted outside it is processed to collagen and assembled into large structures-collagen fibrils
How does collagen interact with cells?
Connective tissue cells that secrete collage also organize collagen in ECM and bind to collagen in ECM through Intergrin (cell surface adhesion receptor) and fibronectin (glycoproteins)
Fibribectin binds to collagen and then it burns to intergrin
Intergrin bunds fibronectin in extracellular domain and binds adaptor proteins (actin filaments) in the intracellular domain
What are the characteristics of Elastin?
It is a fibrous protein, and networks of elastin gives tissues elasticity and stretch and relax like a rubber band. And it also gives resilience.
It provides strength, preventing tissue from excessive stretching
What is a ECM secreted by epithelial cells?
Basil lamina is sepcilized type of ECM and it underlies all epithelia. It’s thin and influences cell polarity
What does basal lamina prevent and allow to pass through it
It prevents fibroblasts in underlying connective tissues from interacting with epithelial cells but lets macrophages and lymphocytes pass through it
What is basil lamina anchored by and organized by?
It is anchored by hemidesmosomes and organized by laminin. It interacts with other components of ECM and links Intergrin to type 4 collagen
What are the main components of a cell wall?
Cellulose: provides tensile strength
Pectin; space filling and provides resistance to compression
Where do plant cells synthesize cellulose
At the plasma membrane and the other wall components are synthesized in Golgi and exported by exocytosis
