Unit 17: Cell Connections

Question 1

describe the structure of cellulose.

Answer 1

made of thin stacked sheets of cellulose microfibrils

Question 2

what does lignin do to cellulose?

Answer 2

adds rigidity and waterproofing

Question 3

wat is turgor pressure?

Answer 3

swelling pressure that develops as a result of osmotic imbalance

Question 4

what determines the direction that a cell grows when water moves in?

Answer 4

the orientation of the cellulose microfibrils

Question 5

is cellulose synthesized inside or outside of the cell?

Answer 5

outside

Question 6

describe the ec matrix in connective tissues.

Answer 6

abundant and carries the mechanical load

Question 7

what provides tensile strength in connective tissues?

Answer 7

fibrous proteins like collagen

Question 8

what is elastin? what is its function?

Answer 8

a rubbery protein in arteries. makes blood vessels resilient while allowing blood flow

Question 9

which protein makes up 25% of animal protein mass?

Answer 9

collagen proteins

Question 10

how many types of collagen proteins are there?

Answer 10

40

Question 11

what collagen makes up 90% of the body’s collagen

Answer 11

type 1

Question 12

what do collagen strands pack into? what do they pack into?

Answer 12

strands pack into fibrils, fibrils pack into fibers

Question 13

what cells make collagen in bone?

Answer 13

osteoblasts

Question 14

what cells make collagen in skin and tendons?

Answer 14

fibroblasts

Question 15

where is procollagen synthesized?

Answer 15

inside the cell, specifically in the endomembrane system

Question 16

what are procollagen proteinases?

Answer 16

extracellular enzymes that cut off the peptide extensions on the end of a procollagen molecule

Question 17

what does the removal of the peptide extensions on the end of a procollagen molecule allow for?

Answer 17

assembly into fibrils outside the cell

Question 18

how is collagen organized in skin?

Answer 18

in a strong wickerwork pattern

Question 19

how is collagen organized in tendons?

Answer 19

in parallel bundles along the major axis of tension

Question 20

how do fibroblasts deposit collagen and rearrange it?

Answer 20

• secrete collagen and pull it, compacting it into sheets and then making long cables
• generates long rage order in EC matrix to generate tendons

Question 21

what are integrins?

Answer 21

transmembrane receptor proteins

Question 22

what do integrins interact with?

Answer 22

extracellularly - literally anything like fibronectin
intracellularly - cytoskeleton

Question 23

what is fibronectin?

Answer 23

an EC matrix protein that has two domains - one of which binds to collagen the other to the integrin

Question 24

what allows a cell to move through a tissue?

Answer 24

forming and breaking of attachments with integrin proteins

Question 25

what causes super elastic skin?

Answer 25

defect in the extracellular proteinases that don't allow for removal of the peptide extent ions in collagen

Question 26

how do matrix proteins cause cancer?

Answer 26

help cancer invade normal tissues

Question 27

how do matrix proteins cause arthritis?

Answer 27

breakdown of cartilage in joints

Question 28

what causes leukocyte adhesion deficiency?

Answer 28

lack of integrin protein on white blood cells not allowing the cells to crawl out of bloodstream to infected tissues

Question 29

what are glycosaminoglycans (GAGs)?

Answer 29

ec matrix molecules that resist compression, most of which form proteoglycans

Question 30

describe the structure of glycosaminoglycans (GAGs).

Answer 30

negatively charged polysaccharide chains of repeating disaccharides

Question 31

how many GAGs are there on aggrecan in cartilage?

Answer 31

100 GAG chains

Question 32

in which areas are there lots of GAGs?

Answer 32

jelly-like connective tissues, like behind the eye

Question 33

in which areas are there not lots of GAGs? what other molecule makes up the rest of the tissue?

Answer 33

in dense, compact connective tissues like tendons and bone . mostly collagen

Question 34

are GAGs hydrophilic or hydrophobic?

Answer 34

strongly hydrophilic

Question 35

what is the function of proteoglycans?

Answer 35

forming gels around cell of varying pore size and charge density that regulate passage of molecules through EC space

Question 36

what are epithelia?

Answer 36

multicellular sheets in which adjacent cells are joined tightly together

Question 37

what is the function of epithelia?

Answer 37

- protective barriers - perform biochemical functions like secretion of products - absorb nutrients - signal detection (light, sound)

Question 38

what is the apical surface?

Answer 38

surface of epithelia that is exposed to air/bodily fluid

Question 39

what is the basal surface?

Answer 39

surface of epithelia that is attached to basal lamina

Question 40

what is the basal lamina?

Answer 40

thin tough sheet of EC matrix mostly made of type IV collagen and laminin protein

Question 41

what is the function of laminin?

Answer 41

adhesive sites for integrin molecules in plasma membrane of epithelial cells

Question 42

what is the function of tight junctions?

Answer 42

seal cells together so nothing leaks out of them

Question 43

tight junctions keep what domains apart to make sure proteins don't diffuse out of the cell?

Answer 43

apical membrane domain and basolateral membrane domain

Question 44

which transmembrane proteins form tight junctions?

Answer 44

claudin and occludin

Question 45

how do claudin and occludin arrange to form tight junctions?

Answer 45

arrange as strands along lines of junction

Question 46

what is the function of cytoskeleton-linked junctions?

Answer 46

binding epithelial cells tgt and to basal lamina

Question 47

what are the three types of cytoskeleton -linked junctions? what do they bind cells to?

Answer 47

adherens - binds cells to eachother desmosomes - binds cells to e/o hemidesmosomes - binds cells to basal lamina

Question 48

what are cadherins?

Answer 48

a family of transmembrane proteins that allow for homophilic binding

Question 49

how is homophilic binding?

Answer 49

when a protein in the plasma membrane of one cell binds to an identical protein in the plasma membrane of another cell

Question 50

which molecule does homophilic binding require to be present in the ec medium?

Answer 50

Ca2+

Question 51

what is an adhering junction?

Answer 51

junction where cadherins are linked to actin filaments via linker proteins in a continuous adhesion belt around cell

Question 52

networks of actin filaments also contain ____ filaments

Answer 52

myosin

Question 53

why is myosin crucial to also be present when we have actin filaments?

Answer 53

- contraction develops tension and changes shape - crucial during embryonic development

Question 54

what usually results when epithelial cells pinch off the sheet creating a hollow tube?

Answer 54

neural structures

Question 55

what are desmosomes?

Answer 55

interactions where cadherins attach to another cell's keratin filaments

Question 56

what are hemidesmosomes?

Answer 56

linkages involving the binding of a cell's integrins to laminin in basal lamina which are then also bound to keratin filaments

Question 57

what is the function of gap junctions?

Answer 57

allowing for inorganic ions and small molecules to pass from cell-cell creating an electrical and metabolic coupling between cells

Question 58

what do gap junctions look like?

Answer 58

regions where the plasma membrane of 2 cells are v close tgt (2-4 nm gap) and exactly parallel - connexons!

Question 59

what are connexons?

Answer 59

water filled channels spanning across membranes in gap junctions

Question 60

what happens to neurons when dopamine is injected?

Answer 60

reduces gap-junction communication between certain neurons in retina in response to increased light going from rod receptors (low light) to cone receptors (bright light)

Question 61

what are plasmodesmata?

Answer 61

small channels that span intervening plant cell walls