BIOL 2020 - actin and microtubules
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What is the role of a cytoskeleton?
To maintain the cell shape, organization and provide support
What are microfilaments made of?
actin
What are microtubules made of?
13 parallel protofilaments right
What are intermediate filaments made of?
keratin
what is tubulin?
a heterodimer formed from two closely related globular proteins
What makes a microtubule stiff and rigid?
The helical lattice due to their orientation giving them polarity
Which end grows in a microtubule?
The plus end
How does rapid microtubule growth occur?
by the addition of tubulin dimers
what is microtubule nucleation?
when multiple tubulin molecules interact to form a microtubule seed- it is a very slow process
what is dynamic instability?
when microtubules alternate between periods of growth and shrinkage
What is the role of Map2 and Tau?
to stabilize microtubule growth
What occurs if there is a mutation in Tau?
a neurodegenerative disease
what is it called when a microtubule goes from growth to shrinkage?
catastrophe
what is it called when a microtubule goes from shrinkage to growth?
rescue
how can we track microtubule dynamics?
through fluorescence microscopy
what does nucleation rely heavily on?
the y-tubulin ring complex
how does nucleation occur?
microtubules are nucleated from the microtubule organizing centre since it is the most enriched with y-tubulin and then worked outwards
where is the y-tubulin kept when not dividing?
centromere
what is the microtubule organizing centre called in an animal cell?
centrosome
What is kinesin?
a tetramer protein that carries cargo towards the plus end of a microtubule
Which part of the kinesin and dynein converts ATP?
the head
Which motor protein makes irregular steps and is large?
dynein
which motor protein makes consistent steps and is small?
kinesin
What is dynein?
a microtubule motor protein that carries cargo towards the minus end
how can we see kinesin dynamics?
through an in-vitro kinesin motility assay
what is different about kinesin-13?
it induces depolarization from both ends and is unable to move. it regulates microtubule dynamics to control spindle assembly
what is different about kinesin-14?
it moves towards the minus end
what must occur for kinesin to move towards the minus end?
kinesin must be inhibited by a kinesin binding protein
What is axonal transport?
when neurons transport vesicles via synapses
how does cilia move?
in a whiplike motion
how does flagella move and where is it found?
in a circular motion and is found on sperm
what are cilia and flagella?
bundles of microtubules
what are the cores of cilia and flagella?
the axoneme which is composed of microtubules and their proteins
what is axonemal dynein?
a protein that bends the axoneme causing cilium and flagellum to move
What does f-actin stand for?
filamentous actin
what does g-actin stand for?
globular actin
what makes up actin?
g-actin subunits
how does actin grow?
from the addition of g-actin on the plus end
what is the rate limiting step in actin formation?
nucleation
what is phalloidin?
a drug that stabilizes f-actin
what is lamellipodia?
a protrusive structure that resembles a branched network
what is filopodia?
a protrusive structure that resembles a tight bundle
what do actin binding proteins regulate?
length and polymerization of filaments
which proteins regulate polymerization?
monomer sequestering proteins and actin-polymerizing proteins
which proteins regulate length?
filament serving proteins and filament capping proteins
what do capping proteins do?
prevent g-actin addition and loss by binding to the plus end
what does cofilin do?
cuts actin filaments into small proteins
what is a-actin?
a rigid cross-linking protein that makes f-actin bundles
what is filamin?
a flexible actin cross-linking protein
what do actin branching proteins do?
make actin branches
what is Arp2/3?
a complex that promotes actin binding by initiating a new branched filament
how is actin cytoskeleton linked to the membrane?
by ERM proteins
what are ERM proteins?
Erzin, radixin and moesin
what needs to happen so that the binding sites for actin on the membrane become exposed?
erzin must be phosphorylated
What are three small GTPase?
rho, rac and Cdc42
what do GTPases signal?
the formation of different actin sturctures
Which proteins regulate the activity of GTPases?
GEF and GAP
Which protein activates Ran-GTP?
GEF actives Ran-GTP by phosphorylating GDP
Which protein inactivates Ran-GTP?
GAP inactivates Ran-GTP by removing a phosphate
What is the common trait among myosin’?
their motor domain
What is the role of MLCK?
phosphorylate the myosin light chains and unfold myosin 2 into its active state
Which type of myosin is unconventional and what does it form?
myosin 2 forms bipolar filaments
what will a mutant of myosin 1 resemble?
left/right introversion
what is the role of myosin 5?
transporting and dispersing cellular cargos
what are stress-fibers?
contractile actin bundles found in non-muscle cells
what is the myosin power stroke?
the force generating step that occurs when phosphate is released