Cell Adhesion and Cell Junction

Question 1

why do we need to study cell adhesion

Answer 1

• need to dissociate cells in order to study them

- spontaneous cell sorting interested scientists

Question 2

cell adhesion vs. cell junction

Answer 2

• cell adhesion are membrane proteins that bind and offer mechanical adhesion
• cell junction are aggregates of transmembrane, intracellular and have other functions like communication

Question 3

major differences between cell adhesion and cell junction

Answer 3

complexity and size

transience and stability

Question 4

functional classification of cell junction

Answer 4

1. anchoring junctions
2. occluding junctions
3. channel forming junctions
4. signal relaying junctions

Question 5

what are the types of anchoring junctions based on attachment sites

Answer 5

actin = adherens (cell-cell) or actin-linked cell matrix adhesions

intermediate filament=
desmosomes (cell-cell)
hemidesmosomes (cell-matrix_

Question 6

what are the adhesion molecule involved in adherens junctions

Answer 6

classical cadherins

Question 7

what are the adhesion molecules associated with desomomes

Answer 7

desmosomal cadherins

Question 8

what are adhesion molecules for focal adhesions

Answer 8

integrins

Question 9

what are some experiments to measure cell adhesion

Answer 9

dual pipette assay
flipping assay
AFM assay
FRET

Question 10

how can we visualize junctions

Answer 10

EM, freeze fracture and transmission

Question 11

steps in preparing freeze fracture

Answer 11

1. tissue fixation and cryoprotection
2. freezing
3. fracturing
4. optional etching
5. replication
6. cleaning of replica to be viewed via EM

Question 12

what are the two faces visualized in freeze fracture

Answer 12

E (ectoplasmic) face

P (protoplasmic face)

Question 13

what do occluding junctions do

Answer 13

restrict passage of molecules between cells

ex: tight junctions

Question 14

how do occluding junctions help maintain polarized localization of membrane proteins

Answer 14

they control the direction of molecules like glucose

Question 15

what are the proteins involved in anchoring junctions

Answer 15

1. transmembrane adhesion proteins
   cadherions/integrins
2. intracellular adaptor proteins
   actin and intermediate filaments

Question 16

how does calcium affect cadherions

Answer 16

it binds in-between the cadherin repeats and aligns them in a tighter, straight line

Question 17

explain mechanotransduction in adherens junctions

Answer 17

the tension of a near by cell pulls on the cadeherin creating tension nd recruiting actin intracellularly

Question 18

what is the difference between hemidesmosomes and desmosomes

Answer 18

desmosomes connect cell to cell and hemi- connect cell to matrix, but both interact with intermediate filaments

Question 19

what are focal contacts

Answer 19

link actin to ECM
important in wound healing
uses integrins and binds to various ECM proteins

Question 20

what are selectins

Answer 20

adhesion molecules that aren’t involved in junctions

mediate weak adhesion
ligands are specific carbs
rapidly deployed
utilized in implantation of embryo and adhesion of leukocytes

Question 21

what is the structure of selection and actin attachment

Answer 21

lectin domain binds EGF domain bind P-selectin in extracellular space. selection is transmembrane and binds anchor proteins and actin in the cytosol

Question 22

what is extravasation

Answer 22

the weak adhesion and rolling of white blood cells (selection dependent) then slipping out into the tissue through strong adhesion and emigration (integrin dependent)