Shemanko Lecture 2

Question 1

Do cells differ in their membranes? What is this called? What does this do?

Answer 1

Yes, polarized cells have differing basal, apical, and lateral membranes.
This provides shape, functional asymmetry, directionality, and is key for migration, development, and organization

Question 2

Where do tight junctions occur?

Answer 2

At the top of the cells between neighboring epithelial cells

Question 3

What can tight junctions do in terms of preventing solute movement?

Answer 3

They prevent solute distribution where different solute concentrations are in adjacent compartments

Question 4

What functions do tight junctions control?

Answer 4

Gate function
Fence function

Question 5

What is a gate function?

Answer 5

Gate functions- control the passage of molecules between cell plasma membrane ex: Claudin 1- tight junction protein, if defected water can’t move through cells and you die
ex: Blood brain barrier- ions or water can’t pass but cells of the immune system can pass

Question 6

What is a fence function? What cell structures does it connect to?

Answer 6

It controls the diffusion of integral mebrane proteins between the apical and basal lateral membranes of 1 cell and maintains cell polarity by blocking apical proteins from going to basal lateral and vice versa
- It connects to the actin cytoskeleton and microtubules

Question 7

How do tight junctions form close contacts between the cells?What structures in the cell do they interact with?

Answer 7

tight junction proteins come from each cell and interact to form the junction, these proteins can interact with actin and microtubules.

Question 8

What do adherens junctions do?

3 things

Answer 8

They connect the external environment to the actin cytoskeleton, provide a pathway for signals to be transmitted from the outside to the cytoplasm and nucelus
They form a belt (zonula adherens) that encircles the cells near the apical surface and adhere cells to eachother

Question 9

What proteins are in adherens junctions?

Answer 9

E-cadherins

Question 10

What are desmosomes? What do they do?

Answer 10

they provide strength to cells by forming a cytoplasmic plaque (made of cadherins and other proteins) which connect to the intermediate filament cytoskeleton that anchors two cells together

Question 11

What type of intermediate filaments are in epithelial cells? What do they do?

Answer 11

Keratin intermediate filaments, they form heterodimers, make long cables, and contribute to strength of the cell and tissue, these heterodimers change with each cell- are specialized

Question 12

mutation in keratin genes can result in what?

Answer 12

skin fragility

Question 13

How are keratin intermediate filaments important in the cytoskeleton of epithelial cells?

Answer 13

K-14 and 5 form a important cytoskeleton for the dividing cells (basal cell keratins) and as we move up the keratins change into a keratin 10 and 1 forming a different cytoskeleton as the cells become more specialized

Question 14

As we move up skin what is the role of the most specified cells? How do dead cells contribute?

Answer 14

they keep hydration through tight junctions and don’t let moisture wick out, dead cells contribute to this by losing nuclei and tight junctions cause a good seal to stop dehydration from inside.

Question 15

What channels do gap junctions form?

Answer 15

intercellular channels

Question 16

What mlcls do gap junctions transmit?

Answer 16

They transmit small <1000 dalton sized signalling molecules through the membrane

Question 17

What are gap junctions channels made of?

Answer 17

connexin proteins, 6 identical connexin proteins from each cell form a transmembrane channel with a central pore -> called a connexon
2 connexons make one gap junctions

Question 18

What do gap junctions pass through?

Answer 18

They pass through adjoining plasma membranes and open into the cytoplasm of the joined cells

Question 19

Are gap junctions present in large amounts? Do they cluster?

Answer 19

yes and yes

Question 20

What interactions involve the cell substratum?

Answer 20

The hemidesmosome and the focal adhesions (for motile cells)

Question 21

Describe hemidesmosomes?

Answer 21

Is a cell matrix attachment seen at the basal surface of epithelial cells and is anchored to the basement membrane, contain a dense cytoplasmic plaque with keratin filaments, keratin filaments are linked to the ECM by integrins (which are unique to hemidesmosomes)

Question 22

What are bp-180?

Answer 22

A protein that is involved in tissue strength, adhesion of cell to extracellular matrix, mutations n this can lead to skin fragility

Question 23

What do focal adhesions do?

Answer 23

they play a key role in cell locomotion, are dynamic structures, they are created for cell to stick on and then disappear when cell leaves.

Question 24

How does focal adhesion help a cell survive?

Answer 24

through focal adhesion kinase and SRC kinase, the interaction of proteins activate these kinases and send a signal to the nucleus that allows for the survival of cells

Question 25

How does a cell going through apoptosis if it leaves substratum help prevent disease?

Answer 25

CELLS THAT BREAK AWAY FROM SBSTRATUM WON’T BE RECIEVEING SRVIVALN SIGNALS FROM INTEGRIN, KILLS THEM TO AVOID SPREAD OF CANCER, focal adhesion helps the cell survive if they adhere.

Question 26

Focal adhesions are connected to what part of the cytoskeleton?

Answer 26

actin