Interactions between cells and their environment

Question 1

how do cell junctions interact with each other and ECM?

Answer 1

Through junctions and these junctions form tissues

Question 2

What junctions are present in Epithelial Cells?

Answer 2

Tight junctions
adherens junctions
desmosomes
gap junctions
hemidesmosomes

Question 3

How are junction arranged in a mature epithelial cell

Answer 3

Tight junctions are nearest to the Apical side they are all along the region of the 2 cells forming a sealing strand

Adherens junctions form cell-cell junctions and also an adhesion belt

Desmosomes are at a specific spots that anchor cells to cells

Hemidesmosomes are also at spots that anchor cells to ECM

Question 4

Tight Junction

Answer 4

seals neighboring cells in an epithelial sheet and prevents materials from leaking through the cell

Composed of 2 transmembrane proteins, claudin and occludin

Claudin sticks to claudin and occludin sticks sticks to occludin

Because these proteins stick to same ones, they form homophilic interactions

Question 5

Adherens junctions

Answer 5

they provide mechanical strength to epithelium

Form an adhesion belt that encircles the inside of the plasma membrane

A cadherin protein attaches to linker proteins and these intracellular linker proteins connect cadherin proteins to actin filaments

Question 6

Desmosomes

Answer 6

join the intermediate filaments in one cell to those in a neighbor

There are 2 parts that make up the desmosomes; the transmembrane adhesion and intracellular linker proteins

The nonclassical cadherin proteins will link to linker proteins which attach to intermediate filaments

Question 7

what is special about the nonclassical cadherins

Answer 7

The cadherins, desmoglein and desmocollin can bind to themselves and each other

Question 8

gap junctions

Answer 8

These allow for communication between cells

Specifically gap junctions form a channel so that cells can share materials

Gap junctions are made up of 6 connexins that form a connexon and 2 connexons from the intracellular channel

Question 9

What do gap junctions allow to pass through the channel

Answer 9

not very selective but allow ion and metabolites that are smaller than 1000 daltons

macromolecules, proteins, and nucleic acids do not pass through

They can be open/closed by signals

Question 10

What happens when cells are broken/cut?

Answer 10

A dramatic influx of calcium will close gap junctions to prevent materials form leaving cells

Question 11

Hemidesmosomes

Answer 11

anchor keratin filaments to basil lamina

They have transmembrane adhesion proteins and linker proteins

The transmembrane proteins are integrins that bind to linker proteins that link integrins to keratin filaments

Question 12

what is the main difference between plant animal cells in terms of cell interactions

Answer 12

plant cells lack cell junctions and instead they have plasmodesmata that cross the cell wall and allow for communication cells

Question 13

Describe the structure of plant cells with plasmodesmata

Answer 13

plant cells share a plasma membrane and ER and the plasmodesmata is a channel that is continuous along 2 cells

callose deposition can make the plasmodesmata more/less permeable

Question 14

Intracellular movement in plant cells

Answer 14

small molecules, sugars, and ions can pass freely and things that are less than 1000 daltons

Question 15

Structure of skin cells

Answer 15

epidermis (epithelium)
basal lamina
Dermis (connective tissue)

Question 16

List the main differences between epithelial cells and connective tissue

Answer 16

Epithelial cells line cavities, intestinal, and skin epidermis and connective tissues are skin dermis, bone, tendon, and cartilage

E.cells have limited ECM and cytoskeletal filaments provide resistance to mechanical stress whereas connective tissue has a lot of ECM that provides resistance mechanical stress

cells in E.cells are usually attached to each other and are closely associated but in connective tissue, cells attach to matrix and are rarely associated

Question 17

what are 3 classes of macromolecules in ECM

Answer 17

Gylcosaminoglycans (GAG) and proteoglycans

Fibrous proteins (collagen, elastin)

Glycoproteins (laminin, fibronectin)

Question 18

Glycosaminoglycans

Answer 18

long, linear chains of 2 different sugars
highly negative
form gas and resist compression
Take up space
Synthesized in cell and released by exocytosis

Question 19

Hyaluron

Answer 19

example of GAG

Question 20

Proteoglycans

Answer 20

They have at least 1 sugar that must be a glycosaminoglycan

Question 21

collagen

Answer 21

fibrous protein

Provides tensile strength and resist stretching

Question 22

Structure of collagen

Answer 22

1. single collagen polypeptide chain
2. 3 single chains form a triple helix
3. this triple helix forms a fibril
4. these fibrils form collagen fibers

Question 23

How is collagen secreted

Answer 23

before it is collagen, it is procollagen

Its structure contains the triple helix with terminal procollagen extensions

Once procollagen is secreted, its terminal extensions are cleaved and assemble in collagen fibrils

Question 24

Fibronectin

Answer 24

Type of glycoprotein that helps link cells to ECM
Integrin dimers are linked to fibronectin by disulfide bonds and there will be a binding site on fibronectin for collagen

Question 25

Elastin

Answer 25

Gives tissue elasticity and resilience

Question 26

What is the difference between plant cell wall and ECM

Answer 26

plant cell wall is rigid and contains cellulose and pectin (polysaccarides)

Question 27

How are cellulose chains added to cell wall

Answer 27

plant cells have a cellulose synthase complex that synthesize cellulose and add them to pre-existing wall

Cellulose provides tensile strength