BSCI330 cell junctions

Question 1

how do squishy cells form structures in multicellular organisms

Answer 1

interactions with the extracellular matrix and their neighbors

Question 2

how are animal cells bound together

Answer 2

connective tissues and epithelial tissues

Question 3

what are the four classes of cell-cell junctions

Answer 3

anchoring, occluding, channel-forming, signal-relaying

Question 4

what are anchorage junctions

Answer 4

cell-cell/cell-matrix adhesion

allow cells to be firmly attached to each other

cadherin or integrin proteins are required

Question 5

what are occluding junctions

Answer 5

permeability barriers - prevent material from passing between two cells (“ziplock bag”)

claudin proteins are required for function

Question 6

what are channel-forming junctions

Answer 6

allow cytosols of two cells to communicate

intercellular passages

connexin or innexin proteins

Question 7

what are signal-relaying junctions

Answer 7

transmit signals

allow signal to be transmitted from one cell to another by secretion of cell-signal molecules in space between two cells

anchorage and signals proteins

Question 8

what do anchorage junctions do

Answer 8

provide mechanical strength to tissues - transmembrane proteins link the cytoskeleton to extracellular structures

Question 9

what are cadherins

Answer 9

adhesive proteins that require calcium to adhere

use homophilic binding - interactions between same types of proteins

Question 10

how are cadherins organized

Answer 10

will sort out in vitro into clumps that are all composed of cells that express the same type or levels of cadherin

Question 11

what do anchor proteins do

Answer 11

connect cadherins to cytoskeleton

Question 12

what do desmoseomes do

Answer 12

helps the intermediate filaments in adjacent cells get connected together, this provides the cells with mechanical strength

Question 13

what are selectins

Answer 13

adhesive protein - weaker adhesion than cadherins but more transient

bind to oligosaccharides on glycoproteins and glycolipids through its lectin domain (calcium dependent)

Question 14

what are integrins

Answer 14

adhesive, heterophilic proteins

bind to adhesions with immunoglobulin-like domains

Question 15

what are selectin-dependent adhesions

Answer 15

weak adhesion and rolling

Question 16

what are integrin-dependent adhesions

Answer 16

strong adhesion and emigration

Question 17

what do occluding junctions do

Answer 17

act as barriers to solute diffusion

their proteins seal the space between adjacent membranes

• act analogous to the seals in Ziploc bags and hold two lipid bilayers together
• the seal is mediated by transmembrane proteins in the bilayers of each cell

Question 18

what proteins form the Ziploc seal in occluding junctions

Answer 18

claudin and occludin

Question 19

what do channel-forming junctions do

Answer 19

are made of proteins such as connexins that connect the cytoplasm of two cells and form small channels

can have small or large gap junctions with few or a lot connexins

Question 20

what do signal-relaying junctions do

Answer 20

help cells communicate quickly, allow cells to communicate with each other in an organized fashion

all the components of other junctions can be in these

Question 21

what is the extracellular matrix called

Answer 21

basal lamina

Question 22

what are the three ways to organize the extracellular matrix

Answer 22

surround cells (like in muscle)

underlie cells (like in epithelium)

between cells (like in kidney glomerulus)

Question 23

what protein organizes the basal lamina

Answer 23

laminins

Question 24

what do integrins do in extracellular matrix

Answer 24

connect it to actin cytoskeleton

Question 25

what are GAGs

Answer 25

sugar polymers that are sulfated to different degrees and form hydrated gels

Question 26

what is collagen

Answer 26

the major protein of the extracellular matrix