Cell Bio exam 4

for 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