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BIOL 2321 - Cell Biology > Cell Junctions > Flashcards

Cell Junctions Flashcards

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1
Q

What 5 things are cell junctions essential for?

A

maintaining positions with the body

giving strength to the tissues

cell-cell communication (signalling)

ECM-cell signalling (info about environment)

sharing of cytoplasm between neighbouring cells

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2
Q

What does the structure of a cell junction depend on?

A

function and environment

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3
Q

what are the 6 types of cell junctions?

A

tight junctions

gap junctions

plasmodesmata

adherens junctions

desmosomes

hemidesmosomes

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4
Q

Where do tight junctions form?

A

at the apex of animal cells between neighbouring epithelial cell

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5
Q

What type of cells have tight junctions and where?

A

at the apex of animal epithelial cells

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6
Q

What is the purpose of tight junctions?

A

they form a water-tight barrier between compartments

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7
Q

How do tight junctions form on the cell?

A

as a series of pockets in a belt around the cell

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8
Q

What are the series of pockets made by tight junctions?

A

intercellular spaces each surrounded by a network of proteins

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9
Q

What do tight junctions prevent?

A

the movement of molecules between cells (paracellular movement) and make it so that only transcellular pathways are available

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10
Q

What is an analogy for tight junctions?

A

gaskets or belts

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11
Q

Describe the structure of tight junctions

A

the integral proteins of tight junctions form continuous fibrils that encircle the cell like a gasket to prevent paracellular movement of molecules between epithelial animal cells

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12
Q

What do the integral proteins of tight junctions make contact with?

A

the neighbouring cells on all sides

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13
Q

What are the two families of proteins important to tight junctions?

A

claudins and occludins

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14
Q

What type of cell junction is essential in forming the blood/brain barrier?

A

tight junctions in endothelial cells of the blood vessels in the brain

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15
Q

T or F: most capillaries do not have tight junctions

A

true except the ones in endothelial cells in blood vessels of the brain

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15
Q

What is the purpose of the tight junctions in the blood/brain barrier?

A

it prevents the passage of molecules into the brain such as ions and water

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16
Q

What can still get through the blood brain barrier? Why?

A

immune cells can send out protein ligands that interact with the tight junction complexes and open them

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17
Q

T or F: tight junctions also maintain structural polarity of epithelial cells

A

True

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18
Q

How do tight junctions help maintain the structural polarity of epithelial cells?

A

the thick band keeps apical membrane proteins from moving too far down the sides of the cells aaand it keeps basolateral membrane proteins from reaching the apical side

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19
Q

What is the zonula occludens?

A

the band of tight junctions around epithelial cells

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20
Q

Describe gap junctions

A

sites of communication between adjoining animal cells

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21
Q

What is the function of gap junctions?

A

intercellular communication

exchange of materials between the two cells

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22
Q

T or F: gap junction proteins in 2 cells are not attached

A

false they are attached to allow intercellular communication and exchange materials between them

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23
Q

Are gap junctions in animal cells or plant cells?

A

animal cells

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24
Q

T or F: there is direct contact between 2 cell membranes because of gap junctions

A

false

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25
Q

What are gap junctions between cells formed by?

A

channels called connexons

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26
Q

How selective are connexons relative to other transport channels

A

less selective - anything small can pass through (ex. second messengers cAMP and IP3)

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27
Q

What kind of molecules can move through connexons? What cannot pass?

A

small molecules like second messengers cAMP and IP3

proteins and RNA are too large to pass

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28
Q

What kind of cells are connexons most often found in?

A

cells that need to act in unison (ex. cardiac muscle or esophagus smooth muscle)

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29
Q

T or F: if even one cell (for cells that need to act in unison) is exposed to a hormone, it can help the stimulus be rapidly transmitted to all cells of the tissue because of gap junctions

A

true

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30
Q

What are connexon channels made of?

A

hexamers of integral membrane proteins called connexins

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31
Q

Describe connexins

A

integral membrane proteins that form hexamers to make connexion channels

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32
Q

What are gap junctions analogous to?

A

ion channels

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33
Q

T or F: connexon channels remain open all the time

A

false! they are like ion channels and they do not remain open all the time

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34
Q

how do connexon channels open?

A

their pore is triggered by stimuli such as voltage change, ligand change, or a pH change

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35
Q

What is the function of plasmodesmata?

A

they are sites of communication between adjoining plant cells that directly connect the two cytoplasms

36
Q

What is the singular word for plasmodesmata?

A

plasmodesma

37
Q

Are plasmodesmata in animal or plant cells?

A

plant

38
Q

When are the plasmodesmata formed?

A

while the cell wall is being built during cytokinesis

39
Q

What animal cell junctions are plasmodesmata similar to?

A

gap junctions

40
Q

What size particles can pass through plasmodesmata?

A

small particles

41
Q

T or F: the channels of plasmodesmata are lined with cell membrane

A

true

41
Q

T or F: the plasmodesmata allows the plasma membrane between two cells to be continuous

A

true

42
Q

How does the plasmodesmata allow the plasma membrane to be continuous between 2 cells?

A

the channels are lined with cell membrane

43
Q

What is the desmotubule?

A

a specialized membrane tube that connects the smooth ER of both cells and widens the pore

44
Q

What are the 3 components of the plasmodesmata?

A

annulus
desmotubule
plasmam membrane

45
Q

Describe the annulus of the plasmodesmata

A

the space around the desmotubule where the cytoplasm and solutes can move freely through the open space around the desmotubule

46
Q

Where are adherens junctions most common?

A

in intestinal epithelial cells of animals

47
Q

What structure do adherens junctions form on a cell?

A

a belt of actin filaments called the zonula adherens just below the zonula occludens

48
Q

What is the zonula adherens?

A

a belt of actin filaments formed by adherens junctions that wraps around the cell just under the zonula of occludins

49
Q

Are adherens junctions in plant or animal cells?

A

animal

50
Q

What is the purpose of adherens junctions?

A

to connect the EC environment to the intracellular actin cytoskeleton

51
Q

Why are adherens junctions important?

A

the connection between the extra- and intercellular environment allow:

cells to maintain their shape within tissue

the actin filaments of one cell to be indirectly linked to the actin filaments in a neighbouring cell - this allows for tissues to use their actin cytoskeleton in a coordinated way

send signals to cell about environment

52
Q

Describe cadherins

A

calcium-binding glycoproteins in the plasma membrane that maintain adherens junctions

53
Q

What are adherens junctions maintained by?

A

calcium-dependent adhesion proteins called cadherins

54
Q

How do cadherins function?

A

they bind to each other like velcro and calcium ions will form bridges between domains of adjacent cadherins

55
Q

Where does calcium bind on cadherins?

A

between the extracellular cadherins domains

56
Q

What does the binding of calcium to cadherins cause?

A

cadherins will become more rigid so that they can stick together like velcro

57
Q

What structure do cadherins have when there is no calcium bound?

A

they are floppy

58
Q

When will cadherins be more likely to bind together or to a cell like velcro?

A

when they are bound to Ca2+ and rigid

59
Q

What does the cytoplasmic domain of cadherin interact with on the inside of the cell membrane?

A

beta catenin

60
Q

What does beta catenin do after it binds with cadherin in the cytosol?

A

it binds to the actin skeleton and can send signals to the nucleus about cell attachment status

61
Q

What does beta catenin do after it binds with cadherin in the cytosol?

A

it binds to the actin skeleton and can send signals to the nucleus about cell attachment status

62
Q

T or F: it doesn’t matter if cells are attached

A

false!! cell attachment is a survival signal!

63
Q

Why is cell attachment a survival signal?

A

if cells become detached from each other, they could become sources of cancer so cell detachment triggers apoptosis

64
Q

Describe desmosomes including their function

A

they are strong junctions in animal cells that form disc-shaped sites of attachment and transmit strength between cells

65
Q

What do desmosomes involve?

A

calcium-dependent attachment between cells via cadherin-like proteins

66
Q

What do desmosomes form?

A

disc-shaped localized sites of attachments (like rivets) that are attached to intermediate filaments

67
Q

T or F: desmosomes, unlike adherens junctions, do not involve calcium-dependent attachment between cells

A

FALSE they do and they use cadherin-like proteins too

68
Q

Which junction is the strongest animal cell junction?

A

desmosomes

69
Q

What is the main purpose of desmosomes?

A

to transmit strength between cells

70
Q

What kind of cells are desmosomes most common in?

A

cells in animal tissues that undergo mechanical stress (they require strength)

71
Q

What is a key difference between desmosomes and adherens junctions?

A

desmosomes connect to intermediate filaments whereas adherens junctions connect to microfilaments (actin filaments)

72
Q

How is calcium involved in desmosome function?

A

Ca2+ binds and makes the EC domains of cadherin-like proteins rigid

73
Q

What happens when Ca2+ binds to the cadherin-like proteins of desmosomes? Where do they bind?

A

on the cytoplasmic side, the cadherin-like proteins attach to a large, dense, button-shaped adaptor protein

74
Q

What do the cadherin-like proteins attach to on the cytoplasmic side of desmosomes? (after calcium has bonded)

A

large, dense, button-shaped adaptor proteins

75
Q

What are the adaptor proteins attached to when the cadherin-like proteins bind to them?

A

intermediate filaments

76
Q

What is the order of the junctions in animal cells from apex to basal lamina?

A

tight junctions

adherens junctions

desmosomes

gap junctions

hemidesmosomes

77
Q

What junction type are hemidesmosomes similar to?

A

desmosomes

78
Q

What is the main difference between hemidesmosomes and desmosomes?

A

hemidesmosomes are between cell and substrate (ECM) whereas desmosomes are between cells

79
Q

Where exactly are hemidesmosomes found?

A

between the basal lamina/basement membrane and the basal surface of epithelial cells

80
Q

Are hemidesmosomes in plant or animal cells?

A

animal epithelial cells

81
Q

What is the main function of hemidesmosomes?

A

anchor epithelial cell to basement membrane

82
Q

What is the tightest attachment between cells and the ECM in the body?

A

hemidesmosomes

83
Q

What proteins are involved with hemidesmosomes?

A

integrins

84
Q

What cytoskeleton component are involved with hemidesmosomes?

A

intermediate filaments

85
Q

What is the function of the integrin proteins involved with hemidesmosomes?

A

they link a button-shaped adaptor protein to the basement membrane through the basal plasma membrane

86
Q

Which junctions are found in animal cells?

A 
tight junctions
gap junctions
adherens junctions
desmosomes 
hemidesmosomes
87
Q

Which junctions are found only in plant cells?

A

plasmodesmata

BIOL 2321 - Cell Biology (26 decks)

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