L4, Cell wall

Question 1

do animal cells have vacuoles?

Answer 1

yes, small ones- mostly

Question 2

what are the functions of a cell wall?

Answer 2

1. gives cells shape, and plant as a whole
2. constrains expansion of protoplast
3. creates turgor pressure
4. physical barrier
5. function as live barriers too (enzymes, chemicals, constantly changing)

Question 3

what are the three cell wall structures?

Answer 3

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

Question 4

during active growth/division of the cell wall, what happens to the primary cell wall?

Answer 4

they are deposited

Question 5

what does the primary cell wall contain?

Answer 5

cellulose, hemicellulose, pectin, and may also contain: enzymes and glycoproteins

Question 6

what are the characteristics of cellulose long fibers?

Answer 6

most abundant macromolecule on Earth,

a polymer,

linear chain of hundreds to thousands of beta (1-4)-linked D-glucose units,

very high energy molecule,

cotton fibers are 90% cellulose

Question 7

what is the structure of cellulose long fibers?

Answer 7

repeating monomers of glucose attached end to end, forming microfibrils (10-25nm) in diameter, have crystalline properties (micelles), and the cellulose microfibrils are wound together (fine threads -> macrofibrils -> cell wall)

Question 8

what are the characteristics of hemicellulose?

Answer 8

random amorphous structure, hydrogen-bonded to cellulose microfibrils, limit extensibility of cell wall which tether adjacent microfibrils to each other, regulate cell expansion

Question 9

what is pectin?

Answer 9

a highly hydrophilic polysaccharide that allows movement during cell expansion and is present in both primary cell wall and middle lamella

Question 10

what prevents further stretching of primary cell wall?

Answer 10

elongation of cell Ca2+ cross-linking of pectins

Question 11

what is the middle lamella?

Answer 11

thin layer between adjacent cells

Question 12

what are the characteristics of the middle lamella?

Answer 12

composed mainly of pectin, difficult to distinguish from primary cell wall, bisected by plasmodesmata in the pit-field

Question 13

what kind of cells is the secondary cell wall present in?

Answer 13

present in cells with strengthening function or role in water transport

Question 14

what is the physical structure of the secondary cell wall?

Answer 14

three-layered, opposing orientation of cellulose

rigid, mostly dead

Question 15

what must the primary cell wall do?

Answer 15

yield and constrain

Question 16

what do expansins in the cell wall do?

Answer 16

loosen structure

Question 17

what are the two main structures of a cell wall when new cellulose microfibrils are placed layer upon layer?

Answer 17

1. amorphous –> ball
2. elongating –> microfibrils deposited in regular plane / perpendicular to axis of elongation

Question 18

how does cellulose growth occur?

Answer 18

via cellulose synthases, form enzyme complexes called rosettes embedded in plasma membrane, using the substrate UDP-glucose (uridine diphosphate glucose)

Question 19

what are the matrix substances?

Answer 19

hemicellulose, pectin, and glycoproteins

carried to wall in secretory vesicles

type of matrix depends on cell secreting the constituents

Question 20

what is involved with cell wall deposition?

Answer 20

lignin and other fortifying structures, cell wall deposition develops over time, cells expand and specialize, vessel elements contain a high concentration of lignin

Question 21

what is the importance of enzymes in cell walls?

Answer 21

can be incredibly specialized in localization, cell corners of fibers, lamellar junctions

Question 22

what toxic substance can the cell wall hold?

Answer 22

sanguinarine - synthesized in cell and stored in cell wall

Question 23

slido question: in the cell wall, ___ molecules unite to form microfibrils

Answer 23

(1-4)-beta-d-glucan chains