2.5: Interactions Between Cells and their Environment Flashcards
epithelial cells interact with each other and the extracellular matrix (ecm) through _______ to form ______
junctions, tissues
state the function of tight junctions
seals neighboring cells together in an epithelial sheet to prevent leakage of extracellular molecules between them; helps polarize cells
state the function of adherens junctions
joins an actin bundle in one cell to a similar bundle in a neighboring cell
state the function of desmosomes
joins the intermediate filaments in one cell to those in a neighbor
state the function of gap junctions
forms channels that allow small, intracellular, water-soluble molecules, including inorganic ions and metabolites to pass from cell to cell
state the function of hemidesmosome
anchors intermediate filaments in a cell to the basal lamina
how are gap junctions different from channels
Diff from channels bc channels connect cytosol and extracellular space
Gap junctions connect cytosol to cytosol
in polarized epithelial cells: are junctions arranged in a specific order or random
specific order
state the two cell-cell anchoring junctions (Attaching neighbouring cells to each other)
adherens junction, desmosome
state which is the cell-ecm anchoring junction (anchoring cell to the basal lamina)
hemidesmosome
what is the purpose of the adhesion belt
to connect a cell to the nearby ones
what is the purpose of the sealing strand (tight junction belt)
All along the cell forming the seal between cell on left and right and front
what is the visible difference between adhesion belt and sealing strand in a diagram
sealing strand is like criss cross and wider, adhesion belt is tighter
which membrane proteins do tight junctions prevent from mixing
the apical and basolateral membrane proteins
tight junctions form __________
sealing strands (tight junction belt)
which 2 transmembrane proteins (4 transmembrane domains weaving back and forth on the membrane) are tight junctions composed of
occludin and claudin
t/f tight junctions can block the movement of molecules from either side
true
are occludin and claudin only able to bind to itself
yes. only occludin-occludin and claudin-claudin on neighboring cells
regarding claudin and occludin, are they required in both cells? and what part of the cell do they interact with?
yes required in both cells, extracellular domain in one cell interacts with extracellular domain in neighbouring cell
transmembrane proteins link to _____________ inside the cel
cytoskeleton
anchoring junctions are able to provide what to the epithelium
mechanical strength
cell-cell anchoring junctions (adherens junctions, desmosomes) link cytoskeletons of ______________
neighboring cells
cell-ecm anchoring junctions (hemidesmosome) link cytoskeleton to ____________
basal lamina
for transmembrane adhesion proteins: what do the extracellular and intercellular domains interact with?
extracellular domains interact with adhesion proteins of neighbouring cells (side) or the ecm (bottom). intracellular domains interact with linker proteins
what is the role of intracellular linker proteins
cytosolic proteins, link transmembrane adhesion proteins to cytoskeletal filaments
each anchoring junction has specific ________________ and _____________
transmembrane adhesion proteins and intracellular linker proteins
_____________ forms an adhesion belt (encircles the inside of the plasma membrane)
adherens junctions
what are cadherins and their purpose
cadherins are transmembrane adhesion proteins. cadherin proteins from neighbouring cells interact with each other, and intracellular linker proteins link cadherin proteins to actin filaments
what protein forms adherens junctions when concentrated at sites of cell-cell interactions
form adherens junctions
compare and contrast between desmosomes and hemidesmosomes
- both link to intermediate filaments eg keratin, intermediate filaments provide the most structural strength
- desmosomes linked to keratin filaments and connect to a neighbouring cell
- hemidesmosomes anchor keratin filaments to the basal lamina (type of ecm)
what filaments provide the most structural strength
intermediate filaments
describe desmosomes: eg what are they, where are they found, what proteins form it
- formed by desmoglein, desmocollin
- desmosomes are transmembrane adhesion proteins, specific cadherin family members (nonclassical)
- intracellular linker proteins link desmoglein and desmocollin to keratin filaments inside the cell (like desmosomes are in between the two cells and then they link to linker proteins that are in the cells which have the keratin anchored to the linker on the cell inside)
can desmoglein and desmocollin only bind to themselves
they can bind to themselves are each other
what composes hemidesmosomes and where do they bind
integrins, bind to laminin in the basal lamina (ecm) – intracellular linker proteins link integrins to keratin filaments inside the cell
differ between the role of intracellular linker proteins with desmosomes and hemidesmosomes
desmosomes: intracellular linker proteins link desmoglein and desmocollin to keratin filaments inside the cell
hemidesmosomes: link integrins to keratin filaments inside the cell
gap junctions allow for __________ between cells
communication
what are gap junctions composed of and describe the order of organization
1 subunit = connexin
6 connexin = form connexon (hemichanell)
2 connexons = intracellular channel (goes perpendicular to plasma membranes)
around what size if the gap of gap junctions
2-4 nm
for gap junctions: how do they couple cells, selectivity, what is allowed passage and what isn’t, any gating?
- couple cells electrically (ions) and metabolically – cytosolic connections
- not very selective as to what passes through: allows ions and metabolites <1000 daltons
- passes through: cAMP, nucleotides, glucose, amino acids
- not pass: macromolecules, proteins, nucleic acids
- are gated - can be open or closed by extracellular or intracellular signals
does dopamine open or close gap junctions
close
does a dramatic increase in cytosolic ca2+ open or close gap junctions
close
does membrane damage open or close gap junctions
membrane damage leads to ca2+ leaking into damaged cells = gap junctions close as to prevent the loss of metabolites from adjacent cells
describe intracellular junctions in plant cells
- lack cell junctions in animal cells
- plants surrounded by cell walls: hold cells tgt and provide mechanical strength
- plasmodesmata: intercellular junctions, allow for communication between cells, but need to cross cell wall (diff structure from gap junctions)
what is the name of the cytoplasmic channels in plant cells and describe it
plasmodesmata - continuous plasma membrane and er across plasmodesmata
explain intercellular movement in plant cells
- plasmodesmata
- small soluble molecules move freely (<1000 daltons) eg sugar, ions, other essential nutrients
- controlled trafficking of large complex molecules under specific conditions: gating for proteins and regulatory RNAs
explain the gating of plant plasmodesmata
gating: eg blocking movement of large complex molecules
ex: enhanced callose (plant polysaccharide) deposition controls permeability through reversible callose deposition – between two cells, callose makes the opening smaller which prevents any movement and also leads to pressure induced displacement (blocking the entrance) on the opposite cell that callose is on
compare and contrast between epithelial tissues and connective tissues
epithelial:
- eg intestinal lining, skin epidermis
- cells closely associated
- cells are attached to each other w junctions and adhesions
- limited ecm (thin basal lamina)
- cytoskeletal filaments provide resistance to mechanical stress
connective tissue:
- eg skin dermis, bone, tendon, cartilage
- cells are rarely connected
- cells attached to matrix
- plentiful ecm
- ecm provides resistance to mechanical stress
what are the 3 classes of macromolecules in the ecm
- glycosaminoglycans (gags) and proteoglycans
- fibrous proteins - collagens, elastin
- glycoproteins - laminin, fibronectin
________ is the primary component in connective tissues
ecm
does the composition of ecm lead to different properties of tissues
yes
describe gags (glycosaminoglycans)
- long, linear, chains of repeating disaccharide
- highly negatively charges (attract na+ and h2o)
- form hydrated gels which resist compression and fills space
- most gags synthesized inside cell and released by exocytosis
what is the key geature of hyaluronan and describe it
key feature: amino sugar
- simple gag
- long chain of repeating disaccharide subunits (up to 25000)
- hyaluronan is spun directly from cell surface by plasma membrane enzyme complex
- in the picture it says 300 nm and (8x10^6)
apart from hyaluronan, give an example of a gag and is key feature
heparin - SO3 attached to CH2O and NH
describe proteoglycans
- subclass of glycoproteins
- protein with at least one sugar side chain which must be a gag
- typically, more extensive addition of sugars (can be up to 95% of total weight)
describe the structure and properties of collagen (fibril forming collagen as the typical collagen)
- fibrous protein
- provides tensile strength
- resist stretching
- 3 chains wound around each other in a triple helix - assemble into ordered polymers to form collagen fibrils (fibrils can pack tgt into collagen dibers)
collagen is secreted as procollagen by _______ (2 answer)
fibroblasts (skin, tendon, other connective tissue), osteoblasts (bone)
once procollagen is secreted, it is processed into ________, which is assembled into large structures called
collagen, collagen fibrils
what are the purposes of the extensions on the end of procollagen in a secretory vesicle
prevents assembly from inside the cell
what cleaves procollagen extensions which then allows it to be become collagen and self assembly into a fibril
procollagen proteinase cleaves terminal procollagen extensions
connective tissue cells that secrete collagen bind to college in ecm through what (2 answers)
integrin (cell surface adhesion receptor) and fibronectin (glycoprotein)
differentiate between how fibronectin and integrin conduct their binding
fibronectin binds to collagen and integrin on specific binding sites
integrin binds to fibronectin through extracellular domains and binds to adaptor proteins (eg actin filaments) through the intracellular domain
state the bond that connects 2 strands of fibronectin
disulfide bonds
name the responsibilities of elastin in the ecm (connective tissue)
- fibrous protein
- networks of elastin: gives tissues elasticity, stretch and relax like a rubber band, gives resilience
other components of ecm: provide strength, prevent tissue from excessive stretching
will the basal lamina always be at the base even if epithelial cells come in diff shapes
yes - epithelial linings can come in many different shapes and sizes - and the basal lamina will always be at the base (if the epithelial is many layers then the basal lamina will be at the bottom of the layers)
ecm is secreted by _______ ______ and influences _______
ecm is secreted by epithelial cells and influences cell polarity
what is the thickness of the basal lamina (epithelial tissue ecm)
very thin, 40-120 nm
state the roles of the basal lamina and its implications
separates epithelia from underlying tissue, prevent fibroblasts in underlying connective tissue from interacting with epithelial cells yet allows passage of macrophages and lymphocytes
the basal lamina is:
the attachment site for ________
anchored by __________
organized by _________
the attachment site for epithelia
anchored by hemidesmosomes
organized by laminin
laminin (glycoprotein) links integrin (transmembrane adhesion protein) to what
links integrin to type IV collagen (fibrous protein)
hemidesmosomes anchor epithelial cells to where
bassal lamina
integrins interact with which glycoprotein to organize the basal lamina
laminin
explain the components of the plant cell wall (+ their contribution to function)
- main components are cellulose and pectin
- cellulose microfibrils provide tensile strength
- pectin fills space and provides resistant to compression
- also has microtubules attached to the plasma membrane
describe the roles and structure of the plant cell wall
- supportive matrix of the plant cell
- plant cells synthesize cellulose chains at plasma membrane (cellulose synthase complex) and the other cell wall components are synthesized in the golgi and exported by exocytosis
- when synthesizing, cellulose microfibrils are being added to preexisting wall
is the plant cell wall or ecm of animal cells more rigid
the plant cell wall
