Cell Bio 406 Lecture 7
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Cell Bio 406 Lecture 7
Cellular Biology 406
What is the cytoskeleton made of?
What does the cytoskeleton being dynamic mean?
it is constantly gaining or loosing units
What does the cytoskeleton form?
a scaffold within the cytoplasm, flagella, cilia, and lamellipodia.
What is the cytoskeleton required for
structure, cell division, signaling, intracellular transport
What are the functions of the cytoskeleton?
generates cell movements and provides mechanical support for the cell
What are the cytoskeletal elements?
microtubules, actin filaments, and intermediate filaments
What are microtubules?
polymers of tubulin subunits
What do microtubules do?
function with molecular motors to move cargo along their surface
What do microtubules do during mitosis?
separate replicated chromosomes
What forms the core of motile structures?
How many chains of subunits make a microtubule?
What are the linear chains of subunits that make up microtubules called?
What stabilizes the microtubule?
lateral bonds between protofilamens
What limits addition and subtraction to microtubule ends?
Which end of microtubules assembles faster?
+ end crowned by b tubulin
What end of a microtubule assembles slower?
the - end crowned by a-tubulin
What is required for microtubule function?
What is dynamic instability?
the switch between phases of growth and shortening of microtubules
Transition from growing to shortening is called?
transition between shortening to growing is called?
What regulates tubulin association and dissocation rates?
GTP or GDP tubulins at microtubule ends
What leads to growth at a microtubule end?
What leads to catastrophe of a microtubule?
transition of GTP to GDP
What forces microtubule end to be straight?
What regulates dynamic instability?
a cap of GTP-tubulin subunits.
what happens to the GTP cap?
It is hydrolyzed to GDP shortly after a sununit adds to a microtubule
What is the bulk of microtubule made of?
What do GTP-tubulins form?
straight protofilaments maintaining adjacent contacts and allowing protofilament growth
What do GDP-tubulins form?
curved protofilaments that break lateral bonds with adjacent subunits.
What is MTOC?
microtubule-organizing center- mediate the nucleation of tubulin into microtubules.
What are centrioles?
contain tubulin and other proteins organized into centrosomes.
What are basal bodies?
a type of MTOC able to organize microtubules into the parallel arrays at the center of cilia and flagellae.
What is different about plant MTOCs?
the microtubles nucleate from microtuble-associated proteins that may be embedded in the nuclear envelope
What is the centrosome?
a pair of centrioles surrounded by the pericentriolar material
What are centrioles?
small barrel shaped organized at right angles i the center of the centrosome
How many microtubules form a centriole?
9 three triplets- one complete A tubule and two partial B and C tubules
What mediates the nucleation of microtubules?
the PCM- pericentriolar material has y-tubulin
What serves as a template for the microtubule at the minus end?
y-tubulin and a number of associated proteins form a large complex (yTuRC)
When is the centrosome duplicated?
What is the MTOC for cilium and flagellum?
What do MTOCs for cillium and flagelum do?
serve as templates for assembly of axoneme.
What is axoneme?
bundle of microtubules that form the core of cilia and flagella and is reponsible for its movement.
What is FRAP used for?
Flouorescent recover after photobleaching is used to track the regrowth of microtubules.
Why do microtubules need to be dynamic?
with motor proteins, they direct cargo to proper destination.
What are molecular motors?
enzymes that generate force and walk along microtubules toward the plus or minus end
What does the head do?
binds microtubules and generates force.
What does the tail do?
binds membrane and other cargo.
Where does kinesis go?
toward the plus end.
Where does dyne in go?
toward the minus end
What is an anchored microtubule for?
What is an anchored motor for?
rearrangement of the cytoskeleton
what mediates binding of cargo?
What associates with the motor to bind cargo?
What regulates microtutuble assembly?
MAPs- Microtubule-associated proteins by stabalizing or destabilizing microtubules.
WHere do MAPs bind?
on the side or at the tip or to the tubulin dimers
How is the activity of MAPs regulated?
What else can MAPs do?
link membranes or protein complexes to microtubules.
How do microtubules and actin function?
they work together during cell locomotion and division
microtubules direct where and when actin assembles or generates contractile forces
What are linker proteins?
bind together actin and microtubules
What controls actin assembly and cell contraction?
subset of G proteins- Rac1 which turns off oncoprotein 18
What does actin do?
creates force in muscle cells
lamellipodia and filopodia of migrating cells
What isoforms are expressed for actin?
alpha in muscles cells
beta and y in non-muscle cells
What is an actin monomer calls?
What is an actin linear polymer calld?
What are the steps to actin polymerization?
nucleation and elongation
What end of actin grows fastest?
What is actin nucleation?
monomer to dimer
what is actin elongation?
what is steady state?
growth and death at same rate.
How does actin cytoskeleton drive motility?
cell controls polymerization and depolymerization
What influences the organization of actin filaments?
Actin binding proteins associate with monomers or filaments
What influences polymerization?
actin monomer-binding proteins
What does profilin do?
asoociates with the barbed end of actin monomers and helps regulate actin polymerization by allowing incorporation of hte monomers only at the barbed end
What controls the time and place of de novo filament formation?
What nucleates filaments in vivo?
Arp2/3 complex generate a branched filament network
formins nucleate unbranched filaments
What regulates the length of actin filaments?
capping proteins inhibit elongation of depolymerization
What caps the pointed end of actin filaments?
How do cross-link proteins work?
organize actin filaments into bundles or orthogonal networks
What do actin bundles do?
help form stereocilia and filopodia
What do actin networks do?
for sheets (lamellae)
What are stereocilia?
similar to villi, they absorb, secrete and mechanically transduce
What are filopodia?
required for cell adhesion to the ECM of migrating cells
what are lamellipodia?
extension of migratory cells
What causes cell locomotion?
What is activated to induce lamellipodia formation?
What is incudes to form filopodia?
What is induces to form contractile filaments?
What is myosin?
actin-based molecular motors that use ATP
What binds loosely to actin?
ATP and ADP-Pi
what causes power stroke?
phosphate release after myosin-ADP-Pi rebinds
What binds strongly to actin?
What determines myosin function?