L7. Cell Junctions

Question 1

What are the 4 different tissue types in the body?

Answer 1

1. epithelium
2. connective
3. muscle
4. nervous

Question 2

What are cell junctions

Answer 2

allow the formation of tissues by connecting cells with other cells

Question 3

Where are cell junctions most prominent?

Answer 3

epithelium cells

Question 4

What locations can cell junctions be in a cell?

Answer 4

• cell-cell interaction

- cell-ECM interaction

Question 5

What types of cell junctions are there ( 3 types)

Answer 5

• occluding ( sealing)
• anchoring
• channel-forming

Question 6

Purpose of the occluding junctions

Answer 6

seal the contacts between cells

Question 7

Purpose of the anchoring junctions

Answer 7

mechanically attach cells together

Question 8

Purpose of the channel forming junctions

Answer 8

allows chemical and electrical junctions to pass through the cells

Question 9

What are the 3 main types of proteins in adhesion complexes? State their characteristics

Answer 9

1. Adaptor protein : allow recruitment of additional components to adhesion proteins, regulate adhesion complex
2. Transmembrane adhesion protein: spans the cell membrane
3. cytoskeletal linkers: physical link between adhesion complex and cytoskeletal linkers

Question 10

Draw the full adhesion complex protein

Answer 10

L7 pg 4b.

Question 11

Name the 4 cell-cell junctions

Answer 11

1. zonular adherins ( anchoring )
2. tight junctions ( sealing)
3. desomosomes ( anchoring)
4. gap junctions ( communicating)

Question 12

Name the 2 cell-ECM junctions

Answer 12

1. focal contacts ( anchoring)

2. hemidesosomes ( anchoring)

Question 13

What are polarized cells

Answer 13

cells that have specialized domains

Question 14

What are the 3 sides of the of the epithelial cell

Answer 14

1. basal
2. lateral
3. apical

Question 15

Draw where the 4 cell-cell junctions are in a polarized cell

Answer 15

L7 pg 6a

Question 16

What composes the junctional complex?

Answer 16

the occluding junctions and anchoring junctions ( ie. desmosomes, tight junctions and zonular adherins)

Question 17

What are the 3 ways that anchoring junction proteins resist the large force of the cell?

Answer 17

1. multi-protein complex: redundancy
2. cluster of adhesion proteins: combined strength
3. link to cytoskeleton (adhesion protein) : large tension bearing protein interaction

Question 18

What is freeze fracture used for?

Answer 18

look at junctional proteins

Question 19

State the process of freeze fracture

Answer 19

1. cells are frozen
2. frozen cells are fractured, fracture is irregular
3. thin layer is sprayed on surface to produce cast
4. organic material is digested by acid- leaving replica
5. replica is examined

Question 20

What is the E-face

Answer 20

inner face of the outer lipid monolayer

Question 21

What is the P-face

Answer 21

inner face of the inner lipid monolayer

Question 22

What is another name for tight junctions?

Answer 22

zonular occludens

Question 23

How are tight junctions formed

Answer 23

tight junctions formed through transmembrane protein interaction

Question 24

What are the 2 proteins that make up the tight junctions?

Answer 24

claudin and occludin

Question 25

Describe claudin

Answer 25

- needed for tight junction formation | - 4-pass transmembrane protein

Question 26

Describe occlaudin

Answer 26

4-pass transmembrane protein receptor barrier function not needed for maintaining tight junction structure

Question 27

What is the function of tight junction

Answer 27

controls solute diffusion between body compartment (eg. glucose transport into blood-glucose blocked by diffusing between the cells -tight junctions, want to actively transport glucose through plasma membrane transporters )

Question 28

What happens when claudin 16 is lost

Answer 28

problem with tight junction calcification in kidney disrupt electrolyte cleaning

Question 29

another name for zonular adherens

Answer 29

adheren junctions

Question 30

What do adheren junctions form?

Answer 30

continuous adhesion belts | 2D sheets of cells

Question 31

What makes adheren junctions/ zonular adherens?

Answer 31

cadherins (adhesion protein) | transmembrane protein

Question 32

What do adheren junctions link to

Answer 32

actin filaments

Question 33

how many pass is an adheren junction

Answer 33

single pass

Question 34

What is the structure of adherin junctions ( draw structure)

Answer 34

the cadherin cluster together (L7. pg 14a)

Question 35

How do adherin junction form?

Answer 35

cadherin molecules bind to other cadherins (aggregate) cadherin extracellular domain straiten with calcium binding cadherin cis-homodimer straightening allows trans homodimerization

Question 36

what is a trans homodimer

Answer 36

when (cadherin) molecule binds another molecule on the surface of ANOTHER cell

Question 37

what is a cis homodimer

Answer 37

when (cadherin) molecule binds another molecule on the surface of the same cell

Question 38

What are catenins?

Answer 38

They are adaptor proteins(INTRACELLULAR anchoring complex) that link the cadherin homodimers to the actin cytoskeleton

Question 39

draw relation between catenin, actin filaments and cadherins

Answer 39

(L7, pg 15b)

Question 40

What happens when cadherins are lost

Answer 40

tumor

Question 41

What is the alternative name of desmosomes

Answer 41

macula adherens

Question 42

What is the adhesion bases for desmosomes

Answer 42

-desmocolin and desmoglein ( cadherin like receptors)

Question 43

Which cytoskeletal element do desmosomes bind to

Answer 43

intermediate filaments (keratin family)

Question 44

What are desmosomes used for

Answer 44

strengthening tissue

Question 45

Where are desmosomes found

Answer 45

tissues exposed to tensile forces

Question 46

Draw the relation between cytoskeleton, intermediate filaments, dsc dsg ,linkers

Answer 46

pg 17 a

Question 47

What is pemphigus vulgaris

Answer 47

loss of dsg : skin blistering

Question 48

What are gap junctions for

Answer 48

allows cells to communicate and share nutrients

Question 49

Aside from epithelial cells where else are gap junctions formed

Answer 49

cardiomyocyte | smooth muscle

Question 50

What makes up gap junctions

Answer 50

connexin: gap junction protein connexon: cluster of 6 connexins

Question 51

What is Vohwinkel Syndrome (keratodema)

Answer 51

Skin is hard and thick | loss of connexin 26