Epithelial Cells

Question 0

Adhering Junctions

Answer 0

zona adherenes; strength to epithelium by linking to actin cytoskeleton of adjacent cells; made of transcellular cadherin proteins; located beneath the tight junctions and form a contractile ring around the cell

Question 1

Tight junctions

Answer 1

lateral side of epithelial cells, made of claudins and occuldins; block movement of molecules and help maintain polarity

Question 2

Gap Junctions

Answer 2

Made from connexion ; allow passage of small molecules and nutrients between cells

Question 3

Basement membrane

Answer 3

thin, non cellular membrane between the epithelium and the connective tissue; made of glycoproteins and proteoglycans; structural support and selective barrier

Question 4

Gap Junctions

Answer 4

Made from connexin- 6 connexins form a unit and interact with connexins unit in opposite cell to form a connexon ; allow passage of small molecules and nutrients between cells (up to 1000 daltons in diameter);

Question 5

Hemidesmosomes

Answer 5

connect cell to basement membrane, transmembrane proteins integrin binds to lamins in extracellular space

Question 6

Extracellular matrix

Answer 6

ECM, made of protein fibers (collagen) and glycoprtoeins that makes a meshwork that surround the cells in the body; a common framework to support a group of cells; cells can change behavior based on the composition of the ECM

Question 7

Cadherin

Answer 7

family of proteins that interact homotypically, i.e. E-cadherin only binds with E-cadherin (epithelial); N with N (neuron); and VE-VE (vascular endotheial- blood vessels); desmosomal cadherin found in desmosomes; cells can be sorted by the type of cadherin they express and how much cadherin they express (stronger binding cadherins localize to center) ; eg how the neural tube is formed (express N cadherin) ; interactions dependant on high calcium to bind to other cadherins ; need clusters to bind (1-1 cadherin too weak to hold cells together)

Question 8

How do cadherins link to actin?

Answer 8

via proteins beta-catenin and alpha catenin

Question 9

How do cadherins link to intermediate filaments?

Answer 9

Proteins plakophilin, plakoglobin, and desmoplakin

Question 10

What is contact inhibition?

Answer 10

when cells make contact they arrest the cell cycle so that organs and tissues won’t be overproliferated with cells; strong interactions between cadherins arrest the cell cycle (cancer cells less tightly attached)

Question 11

How does contact inhibition work?

Answer 11

down regulates Mitogen and Wnt pathways; cadhedrin binds beta catenin to attach to actin in adhering junctions so reduces catenin that would otherwise be used as a transcription factor to express cyclin D

Question 12

What is the Wnt pathway?

Answer 12

normally APC (NOT anaphase promoting complex) phosphorylzes beta catenin and degrades it, but Wnt keeps APC from phos. b catenin and lets cyclin D be transcribed

Question 13

How does Ca2+ effect gap junctions?

Answer 13

gap junctions make it possible to move damage across cells; when calcium enters one cell, it causes connexins to undergo a conformational change and close to prevent damage in other cells

Question 14

What are the most common protein fibers in the ECM?

Answer 14

collagen

Question 15

How do cells bind to the ECM?

Answer 15

Actin in the cell binds to the protein Talin which binds to integrins (a and b subunits) which bind to an ECM fiber

Question 16

How do cells regulate binding to ECM?

Answer 16

integrin is not in correct conformation to bind unless attached to Talin so use expression of talin to regulate when integrin binds or doesn’t bind to ECM; used in immune cells that travel through the body to certain sites

Question 17

Focal Adhesion

Answer 17

cluster of integrin where actin filaments can pull and test fibers to determine how tightly integrin is bound to the ECM and can make decisions according - attract signaling proteins

Question 18

How does ECM stiffness relate to cell survival and proliferation?

Answer 18

Soft ECM triggers apoptosis, growth arrest
Medium ECM triggers migration
Stiff ECM triggers proliferation, spreading, and increases adhesion

Question 19

What types of cells are there?

Answer 19

Epithelial; connective; nervous; and muscle

Question 20

What are the functions of epithelial cells?

Answer 20

Protection, Diffusion, Absorption, Secretion

Question 21

Types of epithelial cells and where they are found

Answer 21

squamous (blood vessels, air sacs of lungs, heart lining, lymphatic vessles)
stratified squamous: (esophagus, mouth, vagina)
cubital (glands and kidney secretary portions)
columnar (usually cilliated, in bronchi and uterus; smooth in intestine and and bladder)
stratified cuboidal : sweat salavary and mamary glands
pseudostratified columnar : ( trachea and upper respitory tract)
Stratified columnar : male urethra and some glands
transitional : (bladder)

Question 22

Claudins

Answer 22

make up tight junctions; span membrane 4 times; linked to actin in cytoskeleton that keeps claudin in place; interactions between claudins generate size restrictive pores; relative “leakiness” of tight junctions depends on what type of claudin is expressed in what cells

Question 23

Relative restrictiveness of claudins

Answer 23

Claudin 5 found in stomach, blood vessels in brain very restrictive bc don’t want acid from stomach lumen to get in ECF or things from body to get in brain
Less restrictive claudins in large intestines, bladder too

Question 24

Function of the basement membrane

Answer 24

ECM component of epi cells; provide:

1) mechanical support
2) regulates activity of epi cells
3) controls access of epi to nutrients (no blood cells so rely on connect with basement membrane to get nutrients like oxygen)
4) Barrier between epi cells and other tissues (keeps cancer from metastisizing)

Question 25

Components of basement membrane

Answer 25

trimers of collagen
trimer of laminins link basement membrane to other structures
perlecan and nidogen link lamin network to collagens
integrins in cell bind laminins in BM

Question 26

Transcytosis

Answer 26

transports materials from apical to basal membranes; allows for translocation of transporters that were put on the wrong side (correct mistakes); and a way to get large macromolecules across the cell

Question 27

What polar end of the microtubles face the apical side?

Answer 27

minus ends so MTOC faces apical side ; can transport along using motor proteins kinesin and dynein

Question 28

How are epithelial cells replaced?

Answer 28

niches at the basal side of the membrane contain stem cells that proliferate and differentiate and move upwards to replace bad cells

Question 29

What are the stem cell niches in intestinal epithelial cells?

Answer 29

crypts at the base of the cells, conditions in crypt different from other parts of cell so lets stem cell proliferate – high amount of mitogent/Wnt that triggers cell division (in apical side have a lot of antimitogens)

Question 30

What is the role of APC in cells?

Answer 30

tumor suppressor protein that degrades b catenin and prevents epithelial cells from dividing by keeping the beta catenin activated genes from being transcribed;
APC is inhibited by Wnt so can’t break down b catenin and you get unopposed cell prolifereration (can’t downregulate cell cycle)