L9

Question 1

what are the 4 structures that hold epithelial cells together

Answer 1

tight junctions

adhering junctions

jap junctions

desmosomes

Question 2

what is the role of microvilli

Answer 2

to increase the surface area

Question 3

what is the role of the basement membrane

Answer 3

it is a supporting cushion for epithelial cells to sit on

Question 4

what is the composition of the lipid bilayer

Answer 4

75% phospholipids
20% cholesterol
5% glycolipids

there are also very small amounts of other lipids

Question 5

where does cholesterol sit in the membrane

Answer 5

it doesn’t have a hydrophobic head region therefore it sits deep in the membrane

Question 6

what is an example of a glycolipid and what is it involved in

Answer 6

GPI is involved in protein trafficking

Question 7

what are some of the roles that other lipids could have in the membrane

Answer 7

cell signalling and trafficking

Question 8

what are the 2 different types of proteins in the lipid bilayer

Answer 8

internal membrane proteins and peripheral membrane proteins

Question 9

describe internal membrane proteins

Answer 9

these span the entire lipid bilayer

eg Na and K channles

Question 10

describe peripheral membrane proteins

Answer 10

these dont span the entire lipid bilayer. they are found inside the cell attached to internal membrane proteins

Question 11

are the membranes static

Answer 11

no

Question 12

what is the mosaic model of the lipid bilayer

Answer 12

Lipid molecules can move
sideways in their own half of the bilayer.

Proteins such as channels,
transporters, receptors, extracellular matrix proteins
etc are embedded in the lipid bilayer, but can also move within the bilayer (eg they can move along it

Question 13

why is the mosaic model possible

Answer 13

because the bilayer is very flexible and dynamic for changing protein and lipid populations, cell growth, secretion and self sealing

Question 14

what is the basement membrane

Answer 14

an extracellular matrix structure

Question 15

what is the order in which you would find joining structures of the epithelial cells going from most apical to basolateral

Answer 15

tight junctions

adhering junction

desosomes

gap junctions

hemidesmosomes

Question 16

what are some characteristics of the basolateral membrane

Answer 16

it is thin, flexible but tough and prevents cell movement

Question 17

where are the proteins needed for the basolateral membrane secreted from

Answer 17

epithelial cells

Question 18

what is epidermolysis bullosa

Answer 18

it is caused by collagen malfunctions so the anchoring of skin epithelial to the basement membrane (through hemidesmosomes) fails and blistering occurs

Question 19

Patients presenting with epidermolysis bullosa present with severe blistering

BECAUSE

collagen dysfunction prevents proper anchoring of basement membrane to the epithelial cell

Answer 19

both are true and related

Question 20

what are the 3 main functions of tight junctions

Answer 20

they act as a

barrier

gate

fence

Question 21

how do tight junctions acts as a barrier

Answer 21

they limit passage of ions and molecules between cells in the parracleeulat pathway (between cells)

Question 22

how do tight junctions acts as a gate

Answer 22

they allow certain solutes to flow through the paracellular pathway

Question 23

how do tight junctions acts as a fence

Answer 23

they prevent the movement of proteins between the apical and basolateral domains

Question 24

what is the importance of tight junctions acting as a fence

Answer 24

it helps to maintain the basal and apical polarity

these membranes need to be different because this is what makes epithelial cells epithelia

Question 25

and tight junctions continuous or random

Answer 25

tight junctions sit close to the apical membrane and form a continuous structure

Question 26

how does the continuous tight junction form

Answer 26

it is formed by stands of claudin proteins linked to lipid bilayers to 2 cells pulling them together

Question 27

what structures are found in tight junctions

Answer 27

JAMs claudin occludin

Question 28

what is the role of JAMs, claudin and occludin

Answer 28

They all connect to proteins called ZO proteins. They then connect to the actin cytoskeleton which is what holds the tight junctions in place

Question 29

are all tight junctions the same

Answer 29

no

Question 30

what is the only structure in the tight junction that changes and how many different types are there

Answer 30

claudin and there are 27 types

Question 31

if a tight junction contains claudin 1 what characteristics will the tight junction have

Answer 31

no transport of ions/water molecules through the paracellular pathway

Question 32

where would tight junctions containing cludin 1 be located

Answer 32

in the skin and glomerulus without them in the skin water would just seep out of us therefore we would die without it

Question 33

what are the characteristics of tight junctions with claudin 2

Answer 33

allows for transport of main ions and water through the paracellular pathway

Question 34

where would tight junctions containing cludin 2 be located

Answer 34

in the intestinal crypts and the proximal renal tubule

Question 35

what are the different names for the adherens junctions

Answer 35

zonular adherens

Question 36

what structure do multiple zonular adherens form

Answer 36

a belt structure just below the tight junctions

Question 37

what is the adherence belt made up of | what filament

Answer 37

actin filaments. it is the CAMs that being the 2 epithelial cells close together

Question 38

formation of adherens junctions initiates what

Answer 38

epithelia formation

Question 39

what is E cadherin

Answer 39

CAM E stands for epithelial

Question 40

explain how E cadherin is related to cancer

Answer 40

E cadherin is important with cancers, breast cancer is an epithelial cancer. As it progresses the Ec loos the epithelial characteristics. This new cell is called mesenchymal. Then the epithelial cells becomes mesenchymal they are able to metastasise The key part that drives this change is the loss of E cadherin causing the loss of formation of these adherence's junctions causing the epithelial cells to become disorganised. When this is what allows the cells to brake off and get into the blood streem and metastasis The cadherins bring the cells together and then these are held in place by anchor proteins from the epithelial cell. These proteins are attached to the actin cytoskeleton

Question 41

describe the characteristics of desmosomes

Answer 41

These hold epithelial cells together in single spots (not continuous) They brings cells together through desmosomal cadherins These are the anchor point for intermediate filaments which are part of the cytoskeleton which is made of keratin

Question 42

where are hemidesmosomes found

Answer 42

joining the basal lamina to epithelial cells

Question 43

what do hemidesmosomes consist of

Answer 43

they are keratin (intermediate) filaments which are embedded in a plaque and joined via the protein plectin to integrins

Question 44

what is the role of the integrins (in relation to hemidesmosomes)

Answer 44

Integrins help to integrate the hemidesmosomes to the basal laminar

Question 45

what are gap junctions

Answer 45

they are tiny channels between cells made of connexin proteins the permit regulated passage of ions and small molecules not continuas they are in single spots

Question 46

what is the difference between a connexin and a connexon

Answer 46

connecOn = a group of six connexIns

Question 47

how small do molecules need to be to move through gap junctions

Answer 47

< 1000 Da

Question 48

what forms a channel | between 2 cells

Answer 48

when a conexon on one epithelial cell lines up with a conexon on another epithelial cell

Question 49

what are the 3 main cytoskeletal types

Answer 49

actin filaments intermediate filaments microtubules

Question 50

what does actin do in the cytoskeleton

Answer 50

it determines cell shape and dives the movement of cells therefore playing a role in cancer migration

Question 51

what is the role of intermediate filaments

Answer 51

provide mechanical strength and resistance to shear stress (Eg when the wind blows your hair up (when its parallel to your head).

Question 52

what is the role of microtubules

Answer 52

to position agranells, railroads for intracellular vesicle transport, form the mitotic spindle and is the motile component of cilia

Question 53

what is an important feature of the cytoskeleton

Answer 53

that it is dynamic and able to adapt to internal and external signals

Question 54

what is the role of accessory proteins in the cytoskeleton

Answer 54

to regulate the assembly and disassembly of things they also link other structures together

Question 55

what do actin filaments consist of

Answer 55

2 stranded helical polymers of actin

Question 56

what is the role of myosins in actin filaments

Answer 56

they are motor proteins that bind to actin filaments and use ATP for contraction, transport proteins, vesicles and organelles along that actin filaments

Question 57

what are microtubules made of

Answer 57

alpha and beta tubulins

Question 58

what are microtubules needed for

Answer 58

cell motility, division and vesical movement

Question 59

what are kinesin and dynein in relation to microtubules

Answer 59

they are molecular motors that allow transport of vesicles and organelles around the cell using ATP they are accessory proteins

Question 60

Desmosomes connect epithelial cells to the basement membrane BECAUSE the basement membrane consists of extracellular matrix proteins

Answer 60

the first is false (should be hemidesmosomes) and the second is true