16.1 Cell Walls

Question 1

many cells are surrounded by () → these surround the plasma membrane and provide rigidity to the outside of the cell

Answer 1

insoluble secreted molecules

Question 2

cells of bacteria, fungi, algae, and higher plants are surrounded by ()

Answer 2

rigid cell walls

Question 3

most cells in animal tissues are surrounded by an (1) that consists of (2)

Answer 3

1. extracellular matrix
2. secreted proteins and polysaccharides

Question 4

main roles of cell walls/extracellular matrix:

Answer 4

1. structural support to cells and tissues
2. mediate interactions between cells

Question 5

(1) consist of polysaccharides cross-linked by short peptides → form a (2) around the entire cell

Answer 5

1. bacterial cell walls
2. covalent shell

Question 6

bacterial cell walls consist of (1) that are cross-linked by (2)

Answer 6

1. polysaccharides
2. short peptides

Question 7

rigidity of cell wall protects against (1) and determines (2) of bacterial cells

Answer 7

1. osmotic pressure
2. characteristic shapes

Question 8

principal component of bacterial cell walls; consists of linear polysaccharide chains cross-linked by short peptides

Answer 8

peptidoglycan

Question 9

for E. coli, peptidoglycan polysaccharide chains are composed of alternating ()

Answer 9

N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) residues

Question 10

how are peptidoglycan polypeptides cross-linked

Answer 10

parallel chains are cross-linked by tetrapeptides attached to the NAM residues

Question 11

an antibacterial compound that worked by inhibiting the enzyme that forms cross-linking tetrapeptides → cell wall synthesis and bacterial growth are prevented

Answer 11

penicillin

Question 12

regulate cell wall synthesis; homologous to microtubules in animal cells

Answer 12

bacterial cytoskeletal proteins

Question 13

how does penicillin function as an antibacterial compound

Answer 13

works by inhibiting the enzyme that forms cross-linking tetrapeptides → cell wall synthesis and bacterial growth are prevented

Question 14

examples of bacterial cytoskeletal proteins

Answer 14

1. FtsZ
2. MreB
3. crescentin

Question 15

bacterial cytoskeletal protein that is involved in cell division, contributes to spherical shape of cell

Answer 15

FtsZ

Question 16

FtsZ is homologous to the eukaryotic () and is found in nearly all bacterial cells

Answer 16

tubulin

Question 17

function of FtsZ in cell division

Answer 17

forms a ring structure at the site where cell division occurs → directs synthesis of a new cell wall that separates the newly formed daughter cells

Question 18

bacterial cytoskeletal protein that is involved in cell elongation; contributes to rod shape of cell

Answer 18

MreB

Question 19

MreB is the homolog of eukaryotic ()

Answer 19

actin

Question 20

bacterial cytoskeletal protein that contributes to curved or spiral shape of cell

Answer 20

crescentin

Question 21

in contrast with bacteria, eukaryotic cell walls (fungi, algae, and higher plants) are composed principally of ()

Answer 21

polysaccharides

Question 22

basic structural polysaccharide of fungal cell walls is () (yeast is a fungus)

Answer 22

chitin

Question 23

chitin is a linear polymer of ()

Answer 23

N-acetylglucosamine residues

Question 24

chitin also forms the (1) and (2)

Answer 24

1. shells of crabs
2. exoskeletons of insects and other arthropods

Question 25

cell walls of most algae and higher plants are composed principally of ()

Answer 25

cellulose

Question 26

cellulose is a linear polymer of ()

Answer 26

glucose residues (often containing more than 10k monomers)

Question 27

most abundant polymer on Earth

Answer 27

cellulose

Question 28

for both chitin and cellulose, sugar monomers are linked by () → allows the formation of long straight chains

Answer 28

beta-1,4 linkages

Question 29

parallel chains of cellulose associate to form long, thin ()

Answer 29

microfibrils

Question 30

within the plant cell wall, cellulose microfibrils are embedded in a matrix consisting of proteins and 2 other types of polysaccharides:

Answer 30

1. hemicelluloses
2. pectins

Question 31

polysaccharide found in matrix within plant cell wall; has rigid components in conjunction with cellulose microfibrils

Answer 31

hemicelluloses

Question 32

rigid hemicelluloses are in conjunction with

Answer 32

cellulose microfibrils

Question 33

polysaccharide found in matrix within plant cell wall; forms a gel-like matrix wherein cellulose microfibrils and hemicelluloses are embedded

Answer 33

pectins

Question 34

hemicelluloses - (1) polysaccharides that are (2) to the surface of cellulose microfibrils

Answer 34

1. highly branched
2. hydrogen-bonded

Question 35

pectins are branched polysaccharides with many ()

Answer 35

negatively charged galacturonic acids

Question 36

how does pectin form gels that cross-link cellulose microfibrils

Answer 36

negative charges bind positive ions (e.g. Ca2+) which trap water molecules

Question 37

one of the critical functions of plant cell walls is to (…)

Answer 37

prevent cell swelling as a result of osmotic pressure

Question 38

because plant cells do not maintain an osmotic balance between their cytosol and extracellular fluids, osmotic pressure continuously drives ()

Answer 38

flow of water into the cell

Question 39

rigid plant cell walls tolerate water influx; aided by an internal hydrostatic pressure that builds up within plant cells

Answer 39

turgor pressure

Question 40

because turgor pressure (…), it is responsible for much of the rigidity of plant tissues and drives expansion of the cell wall

Answer 40

equalizes osmotic pressure and prevents further influx of water

Question 41

turgor pressure equalizes osmotic pressure and prevents further influx of water, thus, it is responsible for much of the (1) and drives (2)

Answer 41

1. rigidity of plant tissues
2. expansion of the cell wall

Question 42

plant cells frequently expand by (1) without synthesizing new (2)

Answer 42

1. taking up water
2. cytoplasmic components

Question 43

cell expansion by mechanism of water uptake is signaled by plant hormones called ()

Answer 43

auxins

Question 44

auxins activate proteins called () that act to weaken a region of the cell wall → allowed turgor pressure to drive the expansion of the cell in that direction

Answer 44

expansins

Question 45

how do expansins allow turgor pressure to drive cell expansion

Answer 45

expansins weaken a region of the plant cell wall, thus allowing turgor pressure to drive cell expansion in that direction

Question 46

how do plant cells expand without increasing cytosolic volume

Answer 46

water flowing into cell is stored in large vacuoles

Question 47

as cells expand, () are deposited outside the plasma membrane

Answer 47

new cell wall components

Question 48

as matrix components (including hemicelluloses and pectins) are synthesized in the Golgi and secreted, cellulose is synthesized by () (transmembrane enzyme complex in the PM)

Answer 48

cellulose synthase

Question 49

cellulose synthase synthesizes cellulose from () in the cytosol

Answer 49

UDP-glucose

Question 50

give an overview of what happens at the cell wall during cell expansion

Answer 50

1. multiple enzyme subunits create a pore through PM
2. growing cellulose chain remains bound to cellulose synthase as it is synthesized and translocated through the pore
3. newly synthesized cellulose microfibrils are deposited perpendicular to the direction of cell elongation

Question 51

cellulose microfibrils in elongating cell walls are laid down in parallel to () underlying the plasma membrane

Answer 51

cortical microtubules