Cell Junctions

Question 1

____ tissues are particularly rich in cell junctions

Answer 1

epithelial

Question 2

cell to cell junctions found in all epithelia

Answer 2

tight junctions

Question 3

tight junctions severely limit ____ and maintain cell membrane ____

Answer 3

intercellular permeability; polarity (different protein components of apical and basolateral membranes)

Question 4

tight junctions are formed by ____ anchored in the membrane

Answer 4

sealing strands

Question 5

tight junctions required for ____ of solutes across the ____

Answer 5

active transport; epithelial barrier

Question 6

all tight junctions impermeable to macromolecules, but permeability to small molecules varies greatly, depending on the number of ____ and the different ____ that comprise them

Answer 6

sealing strands; transmembrane proteins (occludin and claudin families)

Question 7

bind cells to each other and the ECM; found in all tissues, especially those subject to mechanical stress

Answer 7

anchoring junctions

Question 8

types of anchoring junctions

Answer 8

adherens and desmosomes

focal adhesions and hemidesmosomes

Question 9

adherens junctions are cell-cell junctions found primarily in ____; they form a continuous ____ just below the tight junction

Answer 9

epithelia; adhesion belt

Question 10

transmembrane proteins are ____ in adherens junctions

Answer 10

cadherins

Question 11

adherens junctions connect bundles of ____ filaments which are contractile

Answer 11

actin

Question 12

adherens junctions necessary for ____ and _____ in morphogenesis

Answer 12

tight junction formation; epithelial tube formation

Question 13

cell-cell junctions that “rivet” cells together

Answer 13

desmosomes

Question 14

desmosomes are found primarily in ___ and ____; contribute to ___ and ____

Answer 14

epithelia; muscle cells; tissue strength; durability

Question 15

transmembrane proteins in desmosomes are _____

Answer 15

cadherins

Question 16

resemble half-desmosomes, but bind cells to ECM

Answer 16

hemidesmosomes

Question 17

transmembrane adhesion proteins in hemidesmosomes are ____

Answer 17

integrins

Question 18

hemidesmosomes attach the ____ to the ____

Answer 18

junctional epithelium; tooth enamel

Question 19

spot-type junctions that link the cell cytoskeleton to the ECM

Answer 19

focal adhesions

Question 20

focal adhesions transmit external ____ via ____

Answer 20

mechanical signals; integrin receptors

Question 21

focal adhesions are important in:

Answer 21

cell migration, motility, differentiation, proliferation, signal transduction, and orthodontic tooth movement

Question 22

gap junctions are communicating junctions found in nearly all cells except ____ and ____

Answer 22

skeletal muscle; blood cells

Question 23

gap junctions allow ____ and ____ to pass directly from cell to cell

Answer 23

small molecules; electrical charges

Question 24

channels, called ____, are hexamers of ___ proteins

Answer 24

connexons; connexin

Question 25

gap junction permeability can be regulated by intra and extracellular signals

Answer 25

• decrease in cytosolic pH
• large increase in cytosolic free Ca levels
• extracellular signals