Exam 3 Oakes Cytoskeleton II Flashcards
Microtubules:
_______ than actin
Play critical roles in ______ & ______
Microtubules:
More complex than actin
microtubules play a critical role in cell division and transport of proteins throughout the cells
Microtubules:
Explain their structure
Microtubules:
Long, hollow cylinders made of TUBULIN
More rigid than actin
One end is attached to a MTOC or “centrosome”
MTOC serves as a nuckeation site for tubulin to originate from and spread out from inside the cell
Explain Tubulin Structure:
Subunit is a ____
Filaments are ____
___ protofilaments per filament
Tubulin is an ______
Tubulin:
beta stacked ontop of alpha, giving it inherent polarity. Those are stacked ontop of each other, and those protofilaments are put together in a hollow tube
Subunit is a heterodimer (alpha and beta)
Filaments are polarized (beta always on top of alpha)
13 protofilaments per filament
Tubulin is an enzyme, it hydrolyzes GTP
Actin uses what energy source
Tubulin uses what energy source
Actin: ATP
Tubulin: GTP
The lamellapodia, aka the parts of the cell membrane that branch out, those are full of ____, specifically what type?
Lamellapodia: band of actin at the edges of the cell membrane, full of arp 2/3 branched actin
Explain how microtubules undergo hydrolysis (kinda like actin)
What is microtubule catastrophe?
Like actin, microtubules are enzymes that utilize hydrolysis (tubulin uses GTP instead of ATP), polar filament then grows preferentially at one end.
Microtubules will spontanouesly lose their GTP cap (which is a cap at growing end for protection), which results in rapid and stunning depolymerization of the filament
LIKE STRING CHEESE (causes individual protofilaments to peel back from the plus end of the microtubule as if you were peeling string cheese)
Explain microtubule nucleation:
____ acts as a seed pattern to grow the complex microtubule filament
There are a total of _______ in a “lock-washer spiral”
This causes an overlap, creating a “____”
Microtubule nucleation:
gamma-TuRC acts as a seed pattern to grow the complex microtubule filaments
Total of seven copies of gamma-TuSC in a “lock washer spiral”
This causes an overlap/ “seam” shape along the microtubule
About 2 protofilaments per TuSC
Explain how polymerization isn’t truly restricted to just the plus end
Rate limiting step of actin polymerization
Rate limiting step of tubulin polymerization
Actin rate limiting step: formation of the trimer
Microtubules rate limiting: seed forming in tubulin
How many protofilaments are there in a microtubule?
13 protofilaments
Explain the structure of the MTOC/ “centriole:
Centrosome: a collection of roughly 50 gamma tubulin ring complexes located near the nuclease and from which MOST microtubules are nucleated
Typically positioned in front of nucleus along direction of migration
Pair of centrioles inside MTOC
Centrioles: pair of structures consiting of ____ microtubules arranged in a ____ shape
Centrioles are duplicated during ______
Microtubules will self organize with the ____ ends clustered in the center even in the absence of MTOC - this provides a general coordinate system for the cell
Centrioles: pair of structures consisting of 9 microtubules arranged in a barrel shape
Centrioles are duplicated during mitosis
Microtubules will self organize with the minus ends clustered in the center even in the absence of MTOC
Top Hat Question:
Microtubules are different than actin in that…. (think energy)
Microtubules hydrolyze GTP instead of ATP (actin)
Explain the role of kinesin-13 vs XMAP215 in microtubule polymerization
Kinesin 13 promotes destabilization by increasing the frequency of catastrophes
XMAP215 promotes growth (frequency of catastrophes surpressed and growth rate enhanced)
Explain the microtubule crosslinkers:
MAP2 vs tau
What is more spread apart vs more clustered
Microtubule Crosslinkers:
MAP2 gives you more spread out structure
Tau: clustered
Kinesin is a motor protein that moves along microtubules, typically towards ______
Kinesin is structurally similar to ______
Kinesin is a member of a large protein super-family, ____ is the only common element
Kinesin is a motor protein that moves along microtubules, typically towards the + end
Kinesin is structurally similar to myosin
Kinesin is a member of a large protein super family, motor domain is the only common element
Explain the movement of kinesins across microtubules
Just like myosin and actin, kinesins use ATP hydrolysis to move along microtubules
There are two heads, the lagging head binds ATP, once ATP gets hydrolyzed to ADP, then once PI is released (just like on myosin), there is a conformational change where that foot will go in front. ADP falls off the foot in front, and so on and so on
_________ are perfect for carrying cargo, because they kind of walk along the microtubule which acts as a higway to direct trafic
KINESIN is perfect for carrying cargo
one end acts as legs walking down the highway while the other end of the kinesin binds the cargo
Dynein:
Unrelated structurally to myosin and kinesin but still couples _____ to ______
_________ cytoskeletal motor
Typically moves towards ____ end
Defects in transport are associated with
Dyenin:
Unrelated structurally to myosin and kinesin but still couples ATP hydrolysis to motion
MOST POWERFUL cytoskeletal motor
Typically moves towards the — (negative end)
Defects in transport related with a number of diseases
What mades up cilia and flagella?
Function of flagella, cilia
DYENIN and microtubules make up cilia and flagella
Flagella: used to motility, think sperm
Cilia: whip like motion in gut
9 + 2 configuration with additional crosslinks
What are the functions of the two drugs that affect microtubules: taxol and nocodazole
Taxol (chemotherapy): stabilizes microtubules
Nocodazole: depolymerizes by binding subunits
Top Hat Question:
Microtubules play a role in what processes?
A. cargo transport
B. cell division
C. polarity
D. A and B
E. A B and C
Microtubules do ALL three of those things
cargo transport, cell division, and polarity
IFs:
IFs are fromed from elongated molecules with a ________ domain…… ____ protofilaments form the intermedium filament
Lateral contacts make them __________
There are/are not binding sites for nucleotide triphosphates
IFs are formed from elongated molecules with an extended central alpha helical domain with eight protofilaments forming the intermedium filament
Lateral contacts make them difficult to break but easy to bend
There ARE NO binding sites for nucleotide triphosphates (so IFs are not enzymes)
Discuss the roles of IFs
overall role?
plectin
SUN/KUSH
IFs play a role in physical stress. They can oprevent the nucleus from damage. They also play a role in skin cells.
They can be crosslinked to microtubules via plectin
Nuclear IFs can be ancored to microtubules and actin via SUN/KUSH proteins
