37 cytoskeleton Flashcards
what are the 3 main subsystems of the cytoskeleton? (from larges to smallest)
microtubules
intermediate filaments
microfliaments
Microtubule role?
positions organelles involved in cell division
intermediate filaments role?
mechanical strength (less dynamic)
microfilament role?
gives cell shape- microvilli,cell surface and tracks for motor protein myosin
3 subsystems polarity?
microtubules=polar
intermediate filaments=not polar
microfilaments=polar
3 subsystem structures?
microtubules-base unit is alpha and beta tubulin heterodimer, hollow and cylindrical polymers (rigid tubes)
Intermediate filaments- no specific base unit,but helical units and coiled coiled tatramer (filaments interact to make ropelike filaments that can form fibres)
Microfilaments-base unit is G-actin monomer (also hollow tube) and G actins interact to form F (filament) actin. F-actin=2 helices
describe microtubule dynamics for alpha tubulin and beta tubulin
alpha tubulin=always in GTP (bound state)
beta tubulin= binds GTP AND hydrolyses it during polymerisation
consists of catastrophe and rescue
what is catastrophe and rescue?
catastrophe= disassembly which is the same as rapid depolarisation and peeling apart rescue= assembly and rapid repolarisation
Is GTP hydrolysis required growing microtubules? what does a cap of gtp bound subunits do?
yes. GTP hydrolysis triggers conformational change in beta sub unit. This means lattice is under stress and this energy is stored for work. Additionally growing microtubules are stabilized by a Cap of gtp-bound subunits.when the cap is lost the microtubule depolarizes
wjhat happens to microtubules when the cap is lost
it depolarises
why is dynamic assembly crucial
essential for cell division (errors can lead to disease)
define dynamic instability
Dynamic instability refers to the coexistence of assembly and disassembly at the ends of a microtubule. The microtubule can dynamically switch between growing and shrinking phases in this region
how are microtubules organised?
microtubules nucleate out from MTOCs( microtubule organising centres
what is the MTOC called when there is no growth/ground state?
a centromere are there is only 1 MTOC
when cells are dividing how many MTOCs are there and what are they called/
2
spindle poles
where do microtubules grow more quickly from? + or - end?
+ end
what does movement of organelles along microtubules require?
ATP hydrolysis
Motor proteins
what are 2 motor protein example for microtubules?
Kinesin
Dynein
what is the difference between KINESIN and DYNEIN motor proteins in microtubules?
kinesin- needs atp and is processive- only towards + end (stepwise walking)
Dynein-also needs ATP but requires accessory proteins to form Dynactin complex, also only aids growth on - end
colcichine?
from meadow saffron,binds tubulin dimers and inhibits polymerization and relieves joint pain from gout
Taxols?
inhibits mitosis and is used to treat breast and ovary cancer
how do organelles get moved along microtubules?
1) ATP binding site initiates movement of neck linker
2) trailing head hydrolyses ATP
3) ADP is exchanged for ATP on the leading strand to restart the process
Do intermediate filaments bind specific nucleotides?
No
intermediate filaments are tissue specific. give 2 examples
Keratin- hair,nails –> tissue strengt his due to the fact they are rich in disulphide bonds
Lamins- for nuclear lamina, meshwork of integrated proteins, aids shape and stability,interacts with proteins and inner membrane and chromatin, thsi is dissambled during mitosis
do intermediate filaments hav motor proteins?
no. they are not dynamic
what and do actin filaments grow faster at?
+ end
- end is where ADP-actin disassembles from
What do profilin and cofilin do?
profilin is an actin-binding protein involved in the dynamic turnover and restructuring of the actin cytoskeleton –> it recharges ADp-actin
cofilin- binds ADP F actin adn destabilizes filament
explain actin organisation
organised by crosslinking proteins
where do filaments attach to actin?
filaments attach laterally to + end to the plasma membrane
polarity= important
what is treadmilling?
movement by ATP hydrolysis
moltor protein requyired is myosin which always binds actin the same way and moves along actin tracks
what type of motor proteins do microfilaments have?
1 type MYOSIN 9but there are different versions)
myosin 2
muscle contraction
moves to + end
myosin 4
transports vesicular cargo and endocytosis
moves to - end
what are myofibrils
chains of sarcomeres
what are sarcomeres made up of ?
actin and myosin
what has lots of mycofibrils?
skeletal muscle
what drives myosin movement along actin filament?
myosin binds and hydrolyses ATP
what mechanism is used for muscles to contract?
sliding filament mechanism
Explain the sliding filament mechanism of contraction.What is this driven by?
actin filament is anchored to + end to z disc
contraction-actin and myosin slide past each other without shortening. This is driven by myosin heads walking towards + end of actin filament.
what does each cycle of contraction through sliding filament mechanism involve?
myosin binding and hydrolysing 1 ATP molecule
