Cytoskeleton I Flashcards
What is the cytoskeleton?
System of filaments that creates a 3D transport network important for intracellular movement, structural support and control of cell shape
3 classes of cytoskeletal filament
microfilaments
microtubules
intermediate filaments
What are microfilaments made up of?
actin sub units
What are microtubules made up of?
tubulin subunits
Tubulin sub unit structure
alpha-beta heterodimer
What are intermediate filaments made up of?
cytokeratin proteins such as
desmin and vimentin
What type of polymers do the three classes of microfilaments involve?
long unbranched one dimensional polymers
Microtubule diameter
25nm
microfilament diameter
7nm
intermediate filament diameter
10nm
protofilament
filament of polymerised tubulin
13 protofilaments
make up the microtubules found in mammalian cells
Two main functions of intermediate filaments
- structural support
2. determination and maintenance of cell and nucleus shape
Microtubule involvement during interphase (3)
- movement of COP-II vesicles from ER to golgi
- Movement of vesicles through golgi and to the PM
- Movement through the endsomal system
Microtubule involvement during mitosis (1)
- chromosome movement
Which direction do dyneins walk towards?
minus end DN
Which direction do kinesins walk towards?
plus end KP
ER is at the +/- end of microtubule?
+ plus end
Golgi is at the +/- end of microtubule?
- minus end
What protein returns COP-I vesicles from golgi to ER?
kinesins
What protein returns COP-II vesicles from ER to golgi ?
dyneins
150 fold
microtubules are 150 fold more rigid than microfilaments
X
antiparallel tetramer alignment
what are nuclear lamins?
type of intermediate filament protein
where are nuclear lamins located?
forms a lattice-like nuclear lamina at the interface between inner nuclear envelope and chromatin
Function of nuclear lamina?
provides chromatin anchorage surface
Microtubule organising centers (MTOCs)
where minus ends of microtubules are anchored
Which tubulin sub unit can hydrolyse what?
beta tubulin is a GTPase (hydrolyse GTP)
Which tubuline sub unit is at the minus end, the less dynamic end of a microtubule?
alpha tubulin
GTP hydrolysis by beta tubulin is
slow
GTP cap
region at the end of a polymerising microtubule where GTP hydrolysis hasn’t yet occurred
When does a microtubule grow? (shrinks = vice versa)
when polymerisation rate exceeds GTP hydrolysis rate
Dynamic instability
rapid switching between growing (polymerising) microtubules and shrinking (depolymerising) microtubules.
microtubule catastrophe
sudden rapid shortening of microtubule and loss of GTP cap
microtubule rescue
regain GTP cap
What is dynamic instability caused by?
kinetics of GTP hydrolysis
microscopy
used to visualise dynamic growth and depolymerisation of microtubules
gamma tubulin ring complexes
x
How many microtubules in cells in interphase?
50
What can microtubules originate from?
centrosome
MTOCs
Microtubule associated proteins (MAPs)
proteins that regulate tubulin and microtubules and also transport cargo
Catastrophins
proteins associated with disassembly (depolymerisation) of microtubules, even from GTP capped ends
Kinesins walk along microtubules in ? steps
8nm steps
What do kinesins do at each step?
hydrolyse one molecule of ATP
What are mitotic spindles made up of?
microtubules
What are cilia and flagella made of?
microtubules
Basal bodies
microtubular structure originating from a centriole upon which cilia/flagella can assemble
Cilia basal body structure
9 outer doublet microtubules
2 inner singlet microtubules
(9+2 arrangement)
ciliary dynein accessory proteins
ciliary dyneins
large motor complexes present on teh ciliary outer doublet microtubules. Important for driving movement of cilia.
2 functions of cilia and flagella
- motion
2. sensing/signalling
What are bacterial flagella made of?
flagellin
what are eukaryotic flagella made of?
tubulin
microtubule nucleation
x
cellulose thing
x
