Studied by 1 personfor what are cells dependent on the cytoskeleton?
organization, shape, environment interaction, movement
how does the cytoskeleton differ in eukaryotic and prokaryotic cells?
prominent in eukaryotic, in prokaryotic but not complex
what are the three cytoskeletal elements?
intermediate filaments, microtubules, actin filaments
describe intermediate filaments:
in smooth muscle cells
named due to size
prevents cells from shearing apart
where are intermediate filaments prominent?
in the cytoplasm of cells that are subject to mechanical stress
what are the key properties of intermediate filaments?
great strength, extreme durability
what does the great strength of intermediate filaments enable cells to do?
withstand the mechanical stress that occurs when cells are stretched
what does the durability of intermediate filaments allow them to withstand?
a solution of concentrated salts and detergents
what do intermediate filaments typically form?
network through the cytoplasm
what do desmosomes anchor?
intermediate filaments to the plasma membrane
what are the benefits of intermediate filaments found inside the nucleus?
strengthens the nuclear envelope, aids cell cycle regulation
what are lamins?
specialized intermediate filaments
what are the functions of the nuclear lamina?
nuclear membrane support, regulation of cell division
what is the nuclear lamina controlled by?
protein phosphorylation of the lamins
what is the function of protein kinase?
weakens the interactions between the lamin tetramers
what is the function of protein phosphatase?
removes phosphate and promotes reassembly
why is the nuclear lamina targeted in cancer therapies?
prevents disassembly or reassembly, causes apoptosis
what is the function of accessory proteins?
cross links filaments into bundles and connects them to various structures, binds to chromosomes and nuclear lamina
you add a drug to a community of cells that are undergoing mitosis. this drug inhibits activity of the enzyme that phosphorylates nuclear lamina. what do you predict will happen?
what is progeria?
rare disorder that causes individuals to age prematurely
what is progeria caused by?
mutation in the LMNA gene and defect in nuclear lamin
what are microtubules?
long and relatively stiff hollow tubes composed of tubulin dimers
for what functions are microtubules crucial?
cell shape, cell locomotion, intracellular organelle transport, separation of chromosomes during mitosis
what are protofilaments?
dimers stacked together, have structural polarity
what does the centrosome consist of?
a pair of centrioles surrounded by a protein matrix
what does the protein matrix serve as?
a nucleation site (starting part) for the growth of one microtubule
describe the dynamic instability of microtubules:
fluctuate every few minutes between growing and shrinking
how do microtubules become stabilized?
the plus end binding to an accessory protein
what does dynamic instability stem from?
intrinsic capacity of tubulin dimers to hydrolyze GTP
what is the rate of tubulin dimer addition relative to?
the rate of GTP hydrolysis
when do microtubules have a GTP cap?
when GTP bound tubulin dimers are added more rapidly than GTP hydrolysis
what happens to GTP if the rate of polymerization slows?
it will hydrolyze to GDP, causing the GDP tubulin to dissociate
your cells are artificially supplied with nonhydrolyzable GTP. what effect would this have on microtubules?
how do microtubules influence mitosis?
their dynamic nature allows for mitotic spindle formation
how do cells utilize dynamic instability for differentiation?
it is suppressed by proteins that bind to microtubules and protect against disassembly
what is taxol?
cancer drug derived from pacific yew trees
how does taxol modify microtubule dynamics?
prevents tubulin loss
prevents mitotic spindle from shortening during anaphase
arrests cells in mitosis, triggering apoptosis
what are microtubule "roadways" utilized for?
moving transport vesicles and organelles
what is movement controlled by?
motor proteins
what are the most abundant cytoskeletal proteins of MOST cells?
actin filaments
what cell movements are actin filaments essential for?
mechanical support, cell shape, movement of the cell surface
what are actin monomers bound to?
ATP
is ATP an energy source?
NO
what does the hydrolyzation of ATP to ADP cause?
decrease in stability of the monomer in the actin filament
dissociation of filament at its end
what does treadmilling refer to?
the process of adding monomers to the (+) end and removing monomers from (-) end
what does treadmilling dictate?
the size of the actin filament
what do actin-binding proteins control?
location, organization, and behavior of actin filaments
in the budding yeast, activation of the GTP-binding protein Cdc42 occurs on binding of an external signal to a GPCR, promoting actin polymerization. what would happen if you added a toxin that binds to the GPCR?
what occurs simultaneously with protein sorting?
phospholipid synthesis/sorting
where does most protein synthesis begin?
ribosomes in the cytosol
what is the exception to location of protein synthesis?
few mitochondria and chloroplast proteins are synthesized by ribosomes inside the organelle
what does the fate of any protein synthesized in the cytosol depend on?
amino acid sequence (sorting signal)
what is the fate of proteins which lack a sorting signal?
remain permanently in the cytosol
what is the sorting signal?
sequence of 3-60 amino acids, often removed after protein is sorted
what are the two concentric membranes which form the nuclear envelope?
inner nuclear membrane, outer nuclear membrane
describe the inner nuclear membrane:
contains proteins which act as binding sites for chromosomes
provides anchorage for the nuclear lamina
describe the outer nuclear membrane:
similar to the membrane of the ER
continuous with ER
what are nuclear pore complexes?
small polar molecules and macromolecules, highly selective
what are nuclear fibrils?
unstructured regions of nuclear pore complexes
what do nuclear fibrils prevent?
passage of large molecules
what are nuclear localization signals?
specific amino acid sequence of proteins targeted for the nucleus
what is the function of importins a/B (nuclear transport receptors)?
bind to protein, directs it through pore complex
disrupt nuclear fibril interaction, allows passage of nuclear proteins
what does Ran control?
importins movement through the nuclear pore complex
what are the two forms of Ran?
RanGDP and RanGTP
describe RanGDP:
found in cytosol
guided into nucleus via NFT2
catalyzed to exchange GDP for GTP
describe RanGTP:
found in nucleus
decreases importin/protein interaction
binds to importin and guides its transport out of nucleus
catalyzed to hydrolyze GTP to GDP
what controls gene expression?
regulation of import and export of nuclear proteins
how does the mitochondria obtain proteins?
synthesizes them inside mitochondria (1%)
imports from free cytosolic ribosomes (99%)
why is importing of proteins complicated for the cell?
the double membrane of the mitochondria
what does cytosolic Hsp70 recognize?
proteins destined for the mitochondria
how does cytosolic Hsp70 utilize ATP hydrolysis?
to translocate mitochondrial proteins across the outer membrane
what are the two protein sorting pathways?
mim1 translocator, tom complex
what is the mim1 translocator utilized for?
single pass membrane protein in the outer membrane
what occurs as proteins are translocated across the tom complex?
chaperone proteins bind
what is the tim23 complex utilized for?
single pass membrane proteins
how do the tom complex and tim23 complex interact?
translocated protein attaches to tim23 and inserted into the tim23 complex
what is the tim22 complex utilized for?
multipass transmembrane proteins
what is oxal translocase utilized for?
single pass membrane proteins
what does mitochondrial hsp70 guide?
the protein to the oxal translocase
describe how membrane fluidity can affect proteins entering into the mitochondrial matrix:
what are the two pathways for proteins entering the ER:
stays embedded in the membrane OR leaves through the secretory pathway
what happens to proteins once they enter the ER?
they will NOT return to the cytosol
what do proteins require to enter the ER:
ribosomes synthesizing the proteins to be attached to the ER
what are the two protein components which help guide ER signal sequences to the ER membrane?
signal recognition particle (SRP) and SRP receptor
describe the signal recognition particle (SRP):
present in cytosol
bind to both the ribosome and the ER signal sequence as it emerges from the ribosomes
SRP receptor:
embedded in the ER membrane
recognizes the SRP
what are transport vesicles utilized for?
moving proteins to their destination
what are transport vesicles composed of?
phospholipids
what must transport vesicles do:
take with them only proteins appropriate to its destination
recognize and fuse with the appropriate organelle
when do vesicles shed?
after budding is complete
what function does the vesicle coat serve?
captures molecules for onward transport, shapes membrane into bud
what are cargo receptors?
transmembrane proteins that bind soluble proteins for transport
what is the function of adaptins?
secure clathrin coat to vesicle membrane
bind to cargo receptors, select cargo for transport
what is the function of dynamin?
forms ring around neck of each budding vesicle
pinches vesicle
binds GTP
you discover a cell line that forms coated pits of the vesicle but vesicle budding and the removal of the coat does not occur. what component of the budding process could be defective?
what must transport vesicles display in order to ensure specificity?
molecular markers on the cell surface
what are the two families of cytoplasmic microtubule motor proteins?
kinesins and dyneins
which direction do kinesins move in?
towards the plus end
what direction do dyneins move in?
towards the negative end
what is the function of tethering proteins?
bind to rab proteins of the vesicle
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