cell adhesion

Question 1

what are the functions of cell adhesion?

Answer 1

• allow for connections between cells to maintain tissue architecture to counteract external physical forces
• responsible for signaling processes that relay information between cells

Question 2

what are homophilic interactions?

Answer 2

• binding to the same type of molecule
• examples: cadherin, immunoglobulin-superfamily CAMs

Question 3

what are heterophilic interactions?

Answer 3

• binding to different type of molecule
• examples: selectins, mucin-like CAMs, integrin

Question 4

what is the cytoskeletal network made of?

Answer 4

actin, micro, and intermediate filaments

Question 5

what is the velcro principle of adhesion?

Answer 5

• low-affinity binding to ligand
• strength coming from multiple bonds in parallel
• allows for easy disassembly and cells to move around

Question 6

tight junctions

Answer 6

• type of occluding junction
• present in vertebrates only
• found in the apical region of epithelial cells
• form selective barrier to solutes
• involved in maintains the apico-basal polarity of epithelia

Question 7

what do mucin-like CAMs, selectin, and integrin bind to?

Answer 7

• mucin-like CAMs bind to carbohydrates
• integrin binds to fibronectin
• selectins have a lectin domain that bind to carbohydrates

Question 8

tight junction is composed of _______ and ________ molecules that bind in the extracellular space to allow close apposition of the plasma membranes

Answer 8

caludin and occludin

Question 9

__________ of a particular epithelia is a function of the number of sealing strands that it exhibits as well as the _____ protein used

Answer 9

permeability, claudin

Question 10

which two proteins are the main responsible for controlling permeability

Answer 10

occludin and claudin

Question 11

there are approximately __ different claudins

Answer 11

30

Question 12

occludin is present in a ____ _____

Answer 12

single copy

Question 13

examples of diseases affecting claudin and occludin (tight junctions)

Answer 13

hepatitis C and cholera

Question 14

what do mutations in claudin 16 and claudin 14 cause?

Answer 14

• claudin 16: magnesium cannot be absorbed back into body leading to convulsion
• claudin 14: causes deafness

Question 15

function of ZO 1, 2, 3 proteins

Answer 15

link claudin to the actin cytoskeleton to stabilize the tight junction and maintain permeability

Question 16

two main functions of tight junctions

Answer 16

barrier and fence

Question 17

describe barrier and fence

Answer 17

barrier: very selective, only allows specific molecules, separates and maintains extracellular compartments across epithelia
fence: separates apical and basolateral membrane proteins in discrete domains

Question 18

proteins __ ___ intermingle with each other from basolateral to apical

Answer 18

do NOT

Question 19

epithelial cells use tight junctions to control __________ transport

Answer 19

paracellular (passive but selective, variable and regulated)

Question 20

adherens junctions

Answer 20

• type of actin filament attachment sites
• cell-cell junctions
• involved in formation of sheets
• include cadherins

Question 21

classical cadherins

Answer 21

-e-cadherin (epithelial)
- n-cadherin 1 and 2 (neural)
- p-cadherin (placental)

Question 22

classical cadherins attach to actin via adaptor molecules including

Answer 22

• alpha catenin
• beta catenin
• vinculin

Question 23

e-cadherins mediate

Answer 23

calcium dependent adhesion due to L cells lacking endogenous cadherin expression making them not adhere well to one another

Question 24

cadherins are relatively __ _______

Answer 24

low affinity

Question 25

describe selective cell affinity

Answer 25

- based on the idea that cells that express the same cadherin stay together - tissue segregation between cells

Question 26

epithelial tumors have a requirement for _________

Answer 26

loss of cadherin

Question 27

describe why e-cadherin functions as a tumor suppressor

Answer 27

because of its loss-of-function this results in a pre-disposition towards advancing tumorigenesis

Question 28

describe the cadherin switch

Answer 28

“Cadherin switching” is the downregulation of E-cadherins and upregulation of N-cadherins and integrins in EMT (epithelial to mesenchymal transition)

Question 29

explain desmosomes

Answer 29

- they are anchoring junctions (cell-cell junctions) - include the non-classical cadherins desmoglein and desmocoilin - they link to the intermediate filament network and help hold the nucleus in position

Question 30

what is pemphigus vulgaris?

Answer 30

it is a disease of desmosomes where the body attacks itself (auto antibodies to desmoglein 1 and 3). causes a disruption of adhesion between epithelial cells.

Question 31

what are gap junctions?

Answer 31

- most cells are connected to each other by them - create adherence and electrically/chemically couple cells in collectives - small molecules (ex: calcium) and small second messengers (ex: cAMP) can be conducted through gap junction channels - play an important role in the heart tissue and neurons

Question 32

a connexon is formed from ___ ________ _________ in each cell forming a hemichannel

Answer 32

6 connexin subunits

Question 33

how do hemichannels function?

Answer 33

they can function alone in a cell or found in a register with a hemichannel from an adjacent cell forming a junction

Question 34

connexons are opened and closed (permeability) by

Answer 34

post translational modifications (phosphorylation)

Question 35

small molecules less than ______ Daltons in size can pass through gap junctions

Answer 35

1000 (1 kD)

Question 36

extracellular matrix proteins include

Answer 36

proteoglycans, collagens, and multi-adhesive matrix proteins

Question 37

what are the types of collagens?

Answer 37

sheet forming (type IV) and fibrillar (type I, I, III)

Question 38

what is a proteoglycan?

Answer 38

a covalently conjugated molecule (perlecan)

Question 39

what are examples of multi-adhesive matrix proteins?

Answer 39

laminin, fibronectin, nidogen/entactin

Question 40

what is the basal lamina?

Answer 40

it connects most epithelia and other organized groups of cells to adjacent connective tissue. it contains four multidomain proteins (laminin, collagen IV, perlecan, and nidogen).

Question 41

what amino acids make up collagen?

Answer 41

glycine, proline and hydroxyproline

Question 42

what is hydroxyproline important for?

Answer 42

the formation of vitamin C (absence of vit C can lead to scurvy)

Question 43

proteoglycan are composed of

Answer 43

large chains of sugars

Question 44

excessive production of collagen can lead to

Answer 44

struggling with breathing and fibrosis disease (can occur in liver, lungs and pancreas)

Question 45

what are the major types of glycosaminoglycans?

Answer 45

hyaluroan, dermatan sulfate, chondroitin sulfate, keratan sulfate, heparan sulfate.

Question 46

fibronectin structure is composed of

Answer 46

integrin binding, collagen binding and proteoglycan binding

Question 47

integrins are connected to the _____ cytoskeleton and are mediated by _______

Answer 47

actin, talin

Question 48

hemidesmosomes

Answer 48

use plectin to connect to intermediate filaments

Question 49

defects in ________ formation result in server blistering and diseases affecting the epithelia

Answer 49

hemidesmosome

Question 50

what is epidermolysis bullosa?

Answer 50

a blistering disorder causes by defect in hemidesmosome (1 in 50,000 births affected)

Question 51

what is kindler syndrome?

Answer 51

a disease where focal contacts are affected causing excessive proliferation with fluid resulting in blisters