Unit 8: The Cytoskeleton Flashcards
What is the cytoskeleton made up of?
microtubules, actin, and intermediate filaments
Why are filaments not linear?
To be more resistant to breakage
What is the advantage of dynamicity?
Provides ability to rapidly reorganize networks
What is the advantage of static structures?
Provides structural support
How do actin and microtubules help in transporting cellular cargoes.
provide “rail system”
What is the primary role of intermediate filaments
To provide mechanical support and help cells withstand mechanical stress
What motor protein walks toward the minus ends of microtubules
Dynein
What motor protein walks toward the plus ends of microtubules
Kinesin
What two proteins make up microtubules
Tubulin and GTP
What is the function of GTP within a microtubules?
GTP cap forms the growing end of microtubules and when hydrolyzed to GDP, forms the shrinking (depolymerizing end)
When do microtubules form the mitotic spindle?
During mitosis in metaphase
What is the purpose of the centrosome?
Nucelates, anchors, and organizes microtubules.
How do microtubules work in cilia and flagella
drive bending and therefore movement within them
What cellular structures are composed of microtubules
cilia and flagella
What tubulin is added to the plus end of microtubules?
GTP-bound tubulin
What does a GTP cap do and where is it found?
Stabilizes microtubule from depolymerizing
Can be bound by end binding proteins
What occurs when all tubulin in microtubule is GDP-bound
Catastrophe occurs and depolymerazion happens
Whats a benefit of depolymerizing microtubule?
Move chromosomes during anaphase, move mitotic spindle
What allows microtubules to nucleate more efficiently?
Gamma Tubulin ring complex is a template from which microtubules can grow
What do end binding (EB) proteins do?
binds to caps on the plus end of microtubules
What is the purpose of spastin and katanin?
sever/cut microtubules
What is G-actin?
The momomeric form of actin
What is F-actin?
Polymerized G-actin; forms long helical structures
What is treadmilling?
The steady state of actin where:
the plus end gains actin
the minus end loses actin
Where is treadmilling most notable?
at the leading edge of a crawling cell
What subunits are added to the plus end of actin when treadmilling?
ATP-actin
How does actin fall off the minus ends when treadmilling?
The once ATP bound actin is hydrolyzed to ADP bound actin which falls off when exposed to the minus end
What protein(s) causes actin to branch?
Arp2/Arp3 complex proteins
Where are branched actin found?
At the leading edge of a cell which is important for cell migration
How does Cofilin interact with actin?
Twists and Depolymerizes actin
What actin motor walks along F-actin?
Myosin
What are thick filaments in muscle contraction?
Myosin motors
What are the thin filaments in muscle contraction
actin filaments
Which filament has the most tensile strength?
intermediate filaments
Which filament is easily deformed and ruptured?
Microtubules
Which filament is not very flexible and ruptures easily
Actin
How do intermediate filaments strengthen a group of cells?
connect to desmosomes which link neighboring cells
Why are Intermediate filaments non-polar
They have two coiled coils bound that make symmetric tetramer
Which filament is rope-like?
Intermediate filaments
What are nuclear lamins?
subtype of intermediate filaments in the nucleus
How do Lamins protect the nucleus
Protect the nucleus from external forces with a mesh like network under nuclear envelope
What happens when there is a mutation to a lamin
Muscle degeneration diseases
What type of filament is keratin?
Intermediate filament
What happens if there is a mutation of the keratin?
skin cells have looser connections
What are neurofilaments?
intermediate filaments that provide strength and stability to long neuronal processes
What is desmin?
an I.F that supports muscle cells by distributing mechanical force generated by actin and myosin.
How are intermediate filaments different in size to the other two cytoskeleton components?
I.F’s are thicker than actin but smaller than microtubules
What are some cargoes dynein transports?
RNA’s, proteins, vesicles, and the nucleus
How do dynein move along microtubules?
With a power stroke, due to ATP binding and hydrolysis
What does dynein being a “non-processive” motor mean?
It does not go long distances along microtubules
What makes dynein more processive?
Dynein Activator which arranges them into a configuration that is optimal for motility
How do adaptors affect dynein?
Allow dynactin to bind and also links dynein specific cargoes; make sure they bind to the appropriate cargoes
