2.5: Interactions Between Cells and their Environment

Question 1

epithelial cells interact with each other and the extracellular matrix (ecm) through _______ to form ______

Answer 1

junctions, tissues

Question 2

state the function of tight junctions

Answer 2

seals neighboring cells together in an epithelial sheet to prevent leakage of extracellular molecules between them; helps polarize cells

Question 3

state the function of adherens junctions

Answer 3

joins an actin bundle in one cell to a similar bundle in a neighboring cell

Question 4

state the function of desmosomes

Answer 4

joins the intermediate filaments in one cell to those in a neighbor

Question 5

state the function of gap junctions

Answer 5

forms channels that allow small, intracellular, water-soluble molecules, including inorganic ions and metabolites to pass from cell to cell

Question 6

state the function of hemidesmosome

Answer 6

anchors intermediate filaments in a cell to the basal lamina

Question 7

how are gap junctions different from channels

Answer 7

Diff from channels bc channels connect cytosol and extracellular space
Gap junctions connect cytosol to cytosol

Question 8

in polarized epithelial cells: are junctions arranged in a specific order or random

Answer 8

specific order

Question 9

state the two cell-cell anchoring junctions (Attaching neighbouring cells to each other)

Answer 9

adherens junction, desmosome

Question 10

state which is the cell-ecm anchoring junction (anchoring cell to the basal lamina)

Answer 10

hemidesmosome

Question 11

what is the purpose of the adhesion belt

Answer 11

to connect a cell to the nearby ones

Question 12

what is the purpose of the sealing strand (tight junction belt)

Answer 12

All along the cell forming the seal between cell on left and right and front

Question 13

what is the visible difference between adhesion belt and sealing strand in a diagram

Answer 13

sealing strand is like criss cross and wider, adhesion belt is tighter

Question 14

which membrane proteins do tight junctions prevent from mixing

Answer 14

the apical and basolateral membrane proteins

Question 15

tight junctions form __________

Answer 15

sealing strands (tight junction belt)

Question 16

which 2 transmembrane proteins (4 transmembrane domains weaving back and forth on the membrane) are tight junctions composed of

Answer 16

occludin and claudin

Question 17

t/f tight junctions can block the movement of molecules from either side

Answer 17

true

Question 18

are occludin and claudin only able to bind to itself

Answer 18

yes. only occludin-occludin and claudin-claudin on neighboring cells

Question 19

regarding claudin and occludin, are they required in both cells? and what part of the cell do they interact with?

Answer 19

yes required in both cells, extracellular domain in one cell interacts with extracellular domain in neighbouring cell

Question 20

transmembrane proteins link to _____________ inside the cel

Answer 20

cytoskeleton

Question 21

anchoring junctions are able to provide what to the epithelium

Answer 21

mechanical strength

Question 22

cell-cell anchoring junctions (adherens junctions, desmosomes) link cytoskeletons of ______________

Answer 22

neighboring cells

Question 23

cell-ecm anchoring junctions (hemidesmosome) link cytoskeleton to ____________

Answer 23

basal lamina

Question 24

for transmembrane adhesion proteins: what do the extracellular and intercellular domains interact with?

Answer 24

extracellular domains interact with adhesion proteins of neighbouring cells (side) or the ecm (bottom). intracellular domains interact with linker proteins

Question 25

what is the role of intracellular linker proteins

Answer 25

cytosolic proteins, link transmembrane adhesion proteins to cytoskeletal filaments

Question 26

each anchoring junction has specific ________________ and _____________

Answer 26

transmembrane adhesion proteins and intracellular linker proteins

Question 27

_____________ forms an adhesion belt (encircles the inside of the plasma membrane)

Answer 27

adherens junctions

Question 28

what are cadherins and their purpose

Answer 28

cadherins are transmembrane adhesion proteins. cadherin proteins from neighbouring cells interact with each other, and intracellular linker proteins link cadherin proteins to actin filaments

Question 29

what protein forms adherens junctions when concentrated at sites of cell-cell interactions

Answer 29

form adherens junctions

Question 30

compare and contrast between desmosomes and hemidesmosomes

Answer 30

- 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)

Question 31

what filaments provide the most structural strength

Answer 31

intermediate filaments

Question 32

describe desmosomes: eg what are they, where are they found, what proteins form it

Answer 32

- 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)

Question 33

can desmoglein and desmocollin only bind to themselves

Answer 33

they can bind to themselves are each other

Question 34

what composes hemidesmosomes and where do they bind

Answer 34

integrins, bind to laminin in the basal lamina (ecm) -- intracellular linker proteins link integrins to keratin filaments inside the cell

Question 35

differ between the role of intracellular linker proteins with desmosomes and hemidesmosomes

Answer 35

desmosomes: intracellular linker proteins link desmoglein and desmocollin to keratin filaments inside the cell hemidesmosomes: link integrins to keratin filaments inside the cell

Question 36

gap junctions allow for __________ between cells

Answer 36

communication

Question 37

what are gap junctions composed of and describe the order of organization

Answer 37

1 subunit = connexin 6 connexin = form connexon (hemichanell) 2 connexons = intracellular channel (goes perpendicular to plasma membranes)

Question 38

around what size if the gap of gap junctions

Answer 38

2-4 nm

Question 39

for gap junctions: how do they couple cells, selectivity, what is allowed passage and what isn't, any gating?

Answer 39

- 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

Question 40

does dopamine open or close gap junctions

Answer 40

close

Question 41

does a dramatic increase in cytosolic ca2+ open or close gap junctions

Answer 41

close

Question 42

does membrane damage open or close gap junctions

Answer 42

membrane damage leads to ca2+ leaking into damaged cells = gap junctions close as to prevent the loss of metabolites from adjacent cells

Question 43

describe intracellular junctions in plant cells

Answer 43

- 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)

Question 44

what is the name of the cytoplasmic channels in plant cells and describe it

Answer 44

plasmodesmata - continuous plasma membrane and er across plasmodesmata

Question 45

explain intercellular movement in plant cells

Answer 45

- 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

Question 46

explain the gating of plant plasmodesmata

Answer 46

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

Question 47

compare and contrast between epithelial tissues and connective tissues

Answer 47

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

Question 48

what are the 3 classes of macromolecules in the ecm

Answer 48

1. glycosaminoglycans (gags) and proteoglycans 2. fibrous proteins - collagens, elastin 3. glycoproteins - laminin, fibronectin

Question 49

________ is the primary component in connective tissues

Answer 49

ecm

Question 50

does the composition of ecm lead to different properties of tissues

Answer 50

yes

Question 51

describe gags (glycosaminoglycans)

Answer 51

- 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

Question 52

what is the key geature of hyaluronan and describe it

Answer 52

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)

Question 53

apart from hyaluronan, give an example of a gag and is key feature

Answer 53

heparin - SO3 attached to CH2O and NH

Question 54

describe proteoglycans

Answer 54

- 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)

Question 55

describe the structure and properties of collagen (fibril forming collagen as the typical collagen)

Answer 55

- 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)

Question 56

collagen is secreted as procollagen by _______ (2 answer)

Answer 56

fibroblasts (skin, tendon, other connective tissue), osteoblasts (bone)

Question 57

once procollagen is secreted, it is processed into ________, which is assembled into large structures called

Answer 57

collagen, collagen fibrils

Question 58

what are the purposes of the extensions on the end of procollagen in a secretory vesicle

Answer 58

prevents assembly from inside the cell

Question 59

what cleaves procollagen extensions which then allows it to be become collagen and self assembly into a fibril

Answer 59

procollagen proteinase cleaves terminal procollagen extensions

Question 60

connective tissue cells that secrete collagen bind to college in ecm through what (2 answers)

Answer 60

integrin (cell surface adhesion receptor) and fibronectin (glycoprotein)

Question 61

differentiate between how fibronectin and integrin conduct their binding

Answer 61

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

Question 62

state the bond that connects 2 strands of fibronectin

Answer 62

disulfide bonds

Question 63

name the responsibilities of elastin in the ecm (connective tissue)

Answer 63

- 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

Question 64

will the basal lamina always be at the base even if epithelial cells come in diff shapes

Answer 64

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)

Question 65

ecm is secreted by _______ ______ and influences _______

Answer 65

ecm is secreted by epithelial cells and influences cell polarity

Question 66

what is the thickness of the basal lamina (epithelial tissue ecm)

Answer 66

very thin, 40-120 nm

Question 67

state the roles of the basal lamina and its implications

Answer 67

separates epithelia from underlying tissue, prevent fibroblasts in underlying connective tissue from interacting with epithelial cells yet allows passage of macrophages and lymphocytes

Question 68

the basal lamina is: the attachment site for ________ anchored by __________ organized by _________

Answer 68

the attachment site for epithelia anchored by hemidesmosomes organized by laminin

Question 69

laminin (glycoprotein) links integrin (transmembrane adhesion protein) to what

Answer 69

links integrin to type IV collagen (fibrous protein)

Question 70

hemidesmosomes anchor epithelial cells to where

Answer 70

bassal lamina

Question 71

integrins interact with which glycoprotein to organize the basal lamina

Answer 71

laminin

Question 72

explain the components of the plant cell wall (+ their contribution to function)

Answer 72

- 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

Question 73

describe the roles and structure of the plant cell wall

Answer 73

- 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

Question 74

is the plant cell wall or ecm of animal cells more rigid

Answer 74

the plant cell wall