16.1 Cell Walls Flashcards
many cells are surrounded by () → these surround the plasma membrane and provide rigidity to the outside of the cell
insoluble secreted molecules
cells of bacteria, fungi, algae, and higher plants are surrounded by ()
rigid cell walls
most cells in animal tissues are surrounded by an (1) that consists of (2)
- extracellular matrix
- secreted proteins and polysaccharides
main roles of cell walls/extracellular matrix:
- structural support to cells and tissues
- mediate interactions between cells
(1) consist of polysaccharides cross-linked by short peptides → form a (2) around the entire cell
- bacterial cell walls
- covalent shell
bacterial cell walls consist of (1) that are cross-linked by (2)
- polysaccharides
- short peptides
rigidity of cell wall protects against (1) and determines (2) of bacterial cells
- osmotic pressure
- characteristic shapes
principal component of bacterial cell walls; consists of linear polysaccharide chains cross-linked by short peptides
peptidoglycan
for E. coli, peptidoglycan polysaccharide chains are composed of alternating ()
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) residues
how are peptidoglycan polypeptides cross-linked
parallel chains are cross-linked by tetrapeptides attached to the NAM residues
an antibacterial compound that worked by inhibiting the enzyme that forms cross-linking tetrapeptides → cell wall synthesis and bacterial growth are prevented
penicillin
regulate cell wall synthesis; homologous to microtubules in animal cells
bacterial cytoskeletal proteins
how does penicillin function as an antibacterial compound
works by inhibiting the enzyme that forms cross-linking tetrapeptides → cell wall synthesis and bacterial growth are prevented
examples of bacterial cytoskeletal proteins
- FtsZ
- MreB
- crescentin
bacterial cytoskeletal protein that is involved in cell division, contributes to spherical shape of cell
FtsZ
FtsZ is homologous to the eukaryotic () and is found in nearly all bacterial cells
tubulin
function of FtsZ in cell division
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
bacterial cytoskeletal protein that is involved in cell elongation; contributes to rod shape of cell
MreB
MreB is the homolog of eukaryotic ()
actin
bacterial cytoskeletal protein that contributes to curved or spiral shape of cell
crescentin
in contrast with bacteria, eukaryotic cell walls (fungi, algae, and higher plants) are composed principally of ()
polysaccharides
basic structural polysaccharide of fungal cell walls is () (yeast is a fungus)
chitin
chitin is a linear polymer of ()
N-acetylglucosamine residues
chitin also forms the (1) and (2)
- shells of crabs
- exoskeletons of insects and other arthropods
cell walls of most algae and higher plants are composed principally of ()
cellulose
cellulose is a linear polymer of ()
glucose residues (often containing more than 10k monomers)
most abundant polymer on Earth
cellulose
for both chitin and cellulose, sugar monomers are linked by () → allows the formation of long straight chains
beta-1,4 linkages
parallel chains of cellulose associate to form long, thin ()
microfibrils
within the plant cell wall, cellulose microfibrils are embedded in a matrix consisting of proteins and 2 other types of polysaccharides:
- hemicelluloses
- pectins
polysaccharide found in matrix within plant cell wall; has rigid components in conjunction with cellulose microfibrils
hemicelluloses
rigid hemicelluloses are in conjunction with
cellulose microfibrils
polysaccharide found in matrix within plant cell wall; forms a gel-like matrix wherein cellulose microfibrils and hemicelluloses are embedded
pectins
hemicelluloses - (1) polysaccharides that are (2) to the surface of cellulose microfibrils
- highly branched
- hydrogen-bonded
pectins are branched polysaccharides with many ()
negatively charged galacturonic acids
how does pectin form gels that cross-link cellulose microfibrils
negative charges bind positive ions (e.g. Ca2+) which trap water molecules
one of the critical functions of plant cell walls is to (…)
prevent cell swelling as a result of osmotic pressure
because plant cells do not maintain an osmotic balance between their cytosol and extracellular fluids, osmotic pressure continuously drives ()
flow of water into the cell
rigid plant cell walls tolerate water influx; aided by an internal hydrostatic pressure that builds up within plant cells
turgor pressure
because turgor pressure (…), it is responsible for much of the rigidity of plant tissues and drives expansion of the cell wall
equalizes osmotic pressure and prevents further influx of water
turgor pressure equalizes osmotic pressure and prevents further influx of water, thus, it is responsible for much of the (1) and drives (2)
- rigidity of plant tissues
- expansion of the cell wall
plant cells frequently expand by (1) without synthesizing new (2)
- taking up water
- cytoplasmic components
cell expansion by mechanism of water uptake is signaled by plant hormones called ()
auxins
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
expansins
how do expansins allow turgor pressure to drive cell expansion
expansins weaken a region of the plant cell wall, thus allowing turgor pressure to drive cell expansion in that direction
how do plant cells expand without increasing cytosolic volume
water flowing into cell is stored in large vacuoles
as cells expand, () are deposited outside the plasma membrane
new cell wall components
as matrix components (including hemicelluloses and pectins) are synthesized in the Golgi and secreted, cellulose is synthesized by () (transmembrane enzyme complex in the PM)
cellulose synthase
cellulose synthase synthesizes cellulose from () in the cytosol
UDP-glucose
give an overview of what happens at the cell wall during cell expansion
- multiple enzyme subunits create a pore through PM
- growing cellulose chain remains bound to cellulose synthase as it is synthesized and translocated through the pore
- newly synthesized cellulose microfibrils are deposited perpendicular to the direction of cell elongation
cellulose microfibrils in elongating cell walls are laid down in parallel to () underlying the plasma membrane
cortical microtubules
