slide set 14 Flashcards

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1
Q

epithelial tissue vs. connective tissue

A

epithelial tissue: mechanical stresses are transmitted from cell to cell by cytoskeletal filaments anchored to cell-matrix and cell-cell adhesion sites

connective tissue: extracellular matrix directly bears mechanical stresses of tension and compression

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2
Q

type of cell-cell junctions

A

tight junction

adherens junction

desmosome

gap junction

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3
Q

tight junction

A

seals gap between epithelial cells

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4
Q

adherens junction

A

connects actin filament bundle in one cell with that in the next cell

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5
Q

desmosome

A

connects intermediate filaments in one cell to those in the next cell

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6
Q

gap junction

A

allows the passage of small water-soluble molecules from cell to cell

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7
Q

hemidesmosome

A

anchors intermediate filaments in a cell to extracellular matrix

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8
Q

tight junctions

A

made of 2 membrane proteins

claudins: essential for formation
occludins: limit permeability

extracellular domains of each bind tightly to each other

homophilic binding: the proteins bind “self”

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9
Q

tight junctions prevent…

A

small molecules from passing between cells

EX: epithelial cells of small intestine, skin, provide structure to epithelium

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10
Q

tight junctions and diffusion

A

tight junctions can limit membrane protein diffusion to zones within a cell’s plasma membrane

tight junctions confine transport proteins to diff regions of the plasma membrane in epithelial cells of the small intestine

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11
Q

gap junctions

A

pores between cells

allows small molecules to move from one cell to another

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12
Q

how to test if cells are connected by gap junctions

A

inject small dye into one cell

see if dye moves into adjacent cells

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13
Q

types of gap junctions

A

channels, connexons, connexins

2 connexons form a channel

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14
Q

how do cells assemble gap junctions?

A
  • use a fluorescent tag that can be photoconverted from one fluorescent color to another
    • convert the tag on older connexins to green, the remaining connexins are labeled with a red tag
  • new connexons are added to the outside edges of a gap junction
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15
Q

assembling gap junctions

A

new connexons inserted into plasma membrane by exocytosis (like other integral membrane proteins) and then diffuse in the plane of the membrane until they bump into the periphery of a connexon plaque and are trapped

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16
Q

anchoring junctions

A

cells adhere to each other or adhere to the extracellular matrix through anchoring junctions

a cytoskeletal filament attaches to a transmembrane protein through adaptor proteins (cytoskeletal filament can be actin or intermediate filaments)

membrane protein for cell-cell contact is a cadherin protein

membrane protein for cell-ECM is an integrin protein

17
Q

cadherin protein function

A

cell-cell contact

adherens junction

desmosome

18
Q

integrin protein function

A

cell-ECM contact

actin-linked cell-matrix junction

hemidesmosome

19
Q

cadherin protein family

A

share homology domains but also have differences among individuals

cytoplasmic tail varies among family members

extracellular cadherin domain is shared by all cadherins

(domains are fairly rigid, hinge regions in between domains are more flexible)

20
Q

cadherin structure

A

EC region of classic cadherin has 5 copies of extracellular cadherin domain separated by flexible hinge regions

Ca2+ ions bind at each hinge to prevent it from flexing

EC region is rigid and curved

to form cell-cell adhesion, cadherin at N-terminal tip of one cadherin molec binds N-terminal domain from cadherin molec on a diff cell

21
Q

how did we find out structure of cadherin

A

X-ray diffraction

22
Q

role of calcium in cadherin

A

calcium prevents hinge region from flexing

when Ca2+ is bound, there is limited flexibility and EC domain extends away from cell membrane

when Ca2+ isn’t bound, hinge regions are flexible and floppy

23
Q

cadherins are like velcro

A

each protein’s attachment to their partner is relatively weak, but many weak attachments in parallel are strong

24
Q

homophilic binding

A

individual cells bind to cells expressing the same cadherin

25
Q

homophilic binding experiment

A
  1. take cells that don’t express cadherins (L Cells)
  2. Transfect with a plasmid to express E-cadherin or N-cadherin and mix them together

The cells sort themselves into islands!

they sorted themselves by the type and level of cadherins they express

26
Q

cadherin expression changes during development as tissues form

A

as patterns of gene expression change the different groups of cells segregate according to the cadherins they express

27
Q

adherens junctions

A

cytoskeletal filament is actin

adaptor proteins are catenins, which bind to cytoplasmic tail of cadherin and link to actin and associated proteins (including myosin II)

28
Q

mature adherens junction formation

A

100s - 1000s of cadherins

  1. membrane protrusions initiate cell-cell contact
  2. actin and cadherin recruitment expands junction (recruited by Rac)
  3. actin remodeling and myosin recruitment expands the adherens junction
29
Q

tension

A

myosin II and attachments generate tension

2 cells pull equally on each other

cell-cell junctions can sense increased tension and respond by strengthening their actin linkages (tension sensing is done by alpha-catenin)

30
Q

desmosomes

A

cadherins linked to intermediate filaments through adaptors

31
Q

Pemphigus

A

autoimmune disease

patients make antibodies against their own cadherins that form desmosomes

causes severe blistering of skin

keratin intermediate filament networks of adjacent cells are indirectly connected to one another through desmosomes

and to basal lamina through hemidesmosomes