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cell architecture communication and junctions > 37 cytoskeleton > Flashcards

37 cytoskeleton Flashcards

1
Q

what are the 3 main subsystems of the cytoskeleton? (from larges to smallest)

A

microtubules
intermediate filaments
microfliaments

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2
Q

Microtubule role?

A

positions organelles involved in cell division

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3
Q

intermediate filaments role?

A

mechanical strength (less dynamic)

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4
Q

microfilament role?

A

gives cell shape- microvilli,cell surface and tracks for motor protein myosin

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5
Q

3 subsystems polarity?

A

microtubules=polar
intermediate filaments=not polar
microfilaments=polar

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6
Q

3 subsystem structures?

A

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

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7
Q

describe microtubule dynamics for alpha tubulin and beta tubulin

A

alpha tubulin=always in GTP (bound state)
beta tubulin= binds GTP AND hydrolyses it during polymerisation

consists of catastrophe and rescue

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8
Q

what is catastrophe and rescue?

A 
catastrophe= disassembly which is the same as rapid depolarisation and peeling apart
rescue= assembly and rapid repolarisation
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9
Q

Is GTP hydrolysis required growing microtubules? what does a cap of gtp bound subunits do?

A

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

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10
Q

wjhat happens to microtubules when the cap is lost

A

it depolarises

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11
Q

why is dynamic assembly crucial

A

essential for cell division (errors can lead to disease)

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12
Q

define dynamic instability

A

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

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13
Q

how are microtubules organised?

A

microtubules nucleate out from MTOCs( microtubule organising centres

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14
Q

what is the MTOC called when there is no growth/ground state?

A

a centromere are there is only 1 MTOC

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15
Q

when cells are dividing how many MTOCs are there and what are they called/

A

2

spindle poles

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16
Q

where do microtubules grow more quickly from? + or - end?

A

+ end

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17
Q

what does movement of organelles along microtubules require?

A

ATP hydrolysis

Motor proteins

18
Q

what are 2 motor protein example for microtubules?

A

Kinesin

Dynein

19
Q

what is the difference between KINESIN and DYNEIN motor proteins in microtubules?

A

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

20
Q

colcichine?

A

from meadow saffron,binds tubulin dimers and inhibits polymerization and relieves joint pain from gout

21
Q

Taxols?

A

inhibits mitosis and is used to treat breast and ovary cancer

22
Q

how do organelles get moved along microtubules?

A

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

23
Q

Do intermediate filaments bind specific nucleotides?

A

No

24
Q

intermediate filaments are tissue specific. give 2 examples

A

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

25
Q

do intermediate filaments hav motor proteins?

A

no. they are not dynamic

26
Q

what and do actin filaments grow faster at?

A

+ end

- end is where ADP-actin disassembles from

27
Q

What do profilin and cofilin do?

A

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

28
Q

explain actin organisation

A

organised by crosslinking proteins

29
Q

where do filaments attach to actin?

A

filaments attach laterally to + end to the plasma membrane

polarity= important

30
Q

what is treadmilling?

A

movement by ATP hydrolysis

moltor protein requyired is myosin which always binds actin the same way and moves along actin tracks

31
Q

what type of motor proteins do microfilaments have?

A

1 type MYOSIN 9but there are different versions)

32
Q

myosin 2

A

muscle contraction

moves to + end

33
Q

myosin 4

A

transports vesicular cargo and endocytosis

moves to - end

34
Q

what are myofibrils

A

chains of sarcomeres

35
Q

what are sarcomeres made up of ?

A

actin and myosin

36
Q

what has lots of mycofibrils?

A

skeletal muscle

37
Q

what drives myosin movement along actin filament?

A

myosin binds and hydrolyses ATP

38
Q

what mechanism is used for muscles to contract?

A

sliding filament mechanism

39
Q

Explain the sliding filament mechanism of contraction.What is this driven by?

A

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.

40
Q

what does each cycle of contraction through sliding filament mechanism involve?

A

myosin binding and hydrolysing 1 ATP molecule

cell architecture communication and junctions (9 decks)

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