ch 11: cell-cell interactions

Question 1

what is the purpose of an extracellular layer of molecules?

Answer 1

provides structure and withstands tension and compression

Question 2

what is the structure of the extracellular layer?

Answer 2

cross-linked network of long filaments of biomolecules embedded in a stiff surrounding material

Question 3

how many layers to plants have to their cell walls, and what are their names?

Answer 3

1. primary cell wall
2. secondary cell wall
3. middle lamella

Question 4

what does the primary cell wall consist of?

Answer 4

cellulose and pectin

Question 5

purpose of cellulose in the primary cell wall

Answer 5

provides structure and allows the cell to maintain its shape

Question 6

how is the cellulose arranged?

Answer 6

in a crosshatch network (multiple layers)

Question 7

pectin

Answer 7

gelatinious substance that keeps the cell wall moist

Question 8

what are expansins?

Answer 8

they disrupt the hydrogen bonds in the primary cell wall to allow the cell to grow

Question 9

what does cell expansion require?

Answer 9

constant rearrangement of bonds in the polysaccharide network

Question 10

how is the secondary cell wall created?

Answer 10

mature plants secrete molecules to form it

Question 11

where is the secondary cell wall located?

Answer 11

between the plasma membrane and primary cell wall

Question 12

what is the secondary cell wall made of?

Answer 12

in leaves: waxes that protect against losing gases and water
in wood: lignin that withstands gravity and wind

Question 13

in animal cells, what is their extracellular matrix made of?

Answer 13

proteins, glycoproteins, and proteoglycans

Question 14

what does the extracellular matrix assemble into?

Answer 14

collagen or proteoglycans

Question 15

collagen

Answer 15

glycoprotein that is a strong rope-like fibers
- more protein than carbohydrate

Question 16

proteoglycans

Answer 16

gelatinous networks
- more carbohydrate than protein

Question 17

middle lamella

Answer 17

made of gelatinous pectins and is continuous with the primary cell wall

Question 18

what is the purpose of the middle lamella?

Answer 18

connects adjacent plant cells

Question 19

what are the 2 types of membrane proteins connecting animal cells?

Answer 19

1. anchoring or joining junction
2. communicating junctions

Question 20

what are the 2 types of anchoring/joining junctions?

Answer 20

desmosomes and tight junctions

Question 21

what is the communicating junction called?

Answer 21

gap junctions

Question 22

tight junctions

Answer 22

make water-tight seals that do NOT allow for transport

Question 23

how do tight junctions form?

Answer 23

membrane proteins of adjacent cells bind to each other

Question 24

desmosomes

Answer 24

provide stability, flexibility and secure adhesion

Question 25

how do desmosomes form?

Answer 25

by anchoring adhesion proteins at the plasma membrane to the cytoskeleton of two adjacent cells

Question 26

gap junctions

Answer 26

create continuous cytoplasms that allows water, ions, and small molecules (amino acids/nucleotides) to pass freely down their concentration gradient

Question 27

are gap junctions specific?

Answer 27

no, it is just based on whether they can fit through the gap junction

Question 28

do plants have gap junctions?

Answer 28

no

Question 29

what do plants have in place of gap junctions?

Answer 29

plasmodesmata

Question 30

plasmodesmata

Answer 30

communication channels between cells through cell walls

Question 31

what organelle are the plasmodesmata connected by?

Answer 31

the smooth er of two different cells

Question 32

how is transport allowed through the plasmodesmata?

Answer 32

the smooth er is surrounded by a phospholipid bilayer that allows molecules through

Question 33

why are antibodies used to understand cell adhesion?

Answer 33

it shows that specific proteins on the cell surface of the tissue are involved in cell-cell adhesion