microfilaments, microtubules and intermediate filaments Flashcards

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1
Q

what is the structure of a microtubule?

A

13 protofilaments, each polymers of aB-tubulin, which assemble into a hollow tube.
(-) end has an a-subunit exposed, (+) end has B-subunit exposed

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2
Q

what is the difference between the a and B subunits of the tubulin dimer?

A

a- subunit binds a trapped and non-hydrolysable GTP

B-subunit binds an exchangeable and hydrolysable GTP

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3
Q

what is the centrosome?

A

the microtubule organising centre that nucleates the radial array of microtubules in a non-mitotic cell

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4
Q

how do microtubules in a neuronal axon differ from other animal cells?

A

they are non-continuous

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5
Q

what are basal bodies?

A

MTOC of cilia and flagella

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6
Q

what is the role of the gamma tubulin ring complexes?

A

act as a template for microtubule nucleation and allow them to grow outwards

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7
Q

how is GTP hydrolysis involved in microtubule dynamics?

A

GTP hydrolysis changes the conformation of the subunits and weakens bonds in the polymer (cause catastrophe)

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8
Q

how is microtubule dynamics regulated?

A

the + end has a GTP B-tubulin cap, which keeps the microtubule straight and rigid, when the cap is hydrolysed, the protofilaments disassemble due to reduced stability of GDP

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9
Q

what are the roles of MAPs?

A
  • stabilise fillaments (growth)
  • destabilise filaments (catastrophe)
  • link filaments to other molecules or structures
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10
Q

how do we know the (+) end of a microtubule is responsible for dynamics?

A

in vivo, the minus end is anchored and protected at the centrosome

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11
Q

what is the role of kinesin-13?

A

destabilises microtubule ends to enhance the frequency of catastrophes

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12
Q

what are kinesins and how do they work?

A

(+) directed, ATP dependent motor proteins. transport organelles

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13
Q

how does kinesin-1 move?

A

consists of two heavy chains, each with N-terminal motor domain and two light chains that associate with cargo. conformational change upon ATP hydrolysis positions one head domain in front of the other

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14
Q

why is kinesin-1 highly processive?

A

it coordinates ATP hydrolysis between its two heads so that one head is always firmly bound to a microtubule

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15
Q

what are dyneins and how do they work?

A

minus end directed motor proteins, utilise a dynactin complex to link motor to cargo. utilise adaptor proteins to bind a variety of cargoes.

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16
Q

give three methods to investigate protein function

A

1) use an inhibitor
2) express a mutant that impairs protein function
3) knock down protein expression via RNAi

17
Q

what is nocodazole?

A

a microtubule inhibitor that depolymerises them by binding to free a/B dimers and prevents their incorporation into growing microtubules

18
Q

what is EHNA?

A

a dynein inhibitor

19
Q

how can kinesin function be studied by expressing a mutant protein?

A

generation of a dominant negative mutant which lacks head domain, and binds cargo to the tail domain. this mutant outcompetes endogenous protein and prevents transportation of cargo

20
Q

give an example of a MAP

A

the tau protein family stabilise and cross-link microtubules. they are highly expressed in neurons and bind to the side of the MT, keeping it straight and rigid

21
Q

list the functions of microtubules

A
  • main determinants of intracellular organisation and movement
  • positioning of organelles
  • intracellular trafficking of molecules
  • cellular polarity
  • they form the mitotic spindle during mitosis
22
Q

explain how positioning of the endoplasmic reticulum is controlled by microtubules

A

endoplasmic reticulum is carried to the periphery of the cell by kinesins

23
Q

what processes occur in the nucleus?

A

DNA replication

chromatin re-organisation and modification

24
Q

outline the structure of the inner and outer nuclear membranes

A

inner and outer membranes are continuous, yet maintain distinct protein compositions.
-inner membrane: binding sites for chromosomes and nuclear lamina
outer membrane: studded with ribosomes for protein synthesis

25
Q

how is peripheral heterochromatin silenced?

A

anchorage of peripheral heterochromatin to periphery and interaction with nuclear lamina

26
Q

where is actively transcribed chromatin found?

A

centre of the nucleus

27
Q

what is the role of the nuclear lamina?

A

provides structural support for nuclear envelope and anchors chromosomes to cytoskeleton

28
Q

what is the role of the nucleolus?

A

responsible for transcription and processing of non-coding RNAs: rRNAs, tRNAs and snRNAs. alongside ribosomal subunit assembly

29
Q

what is the role of nuclear pore complexes?

A

control movement in and out of the nucleus

30
Q

describe the structure of a nuclear pore complex

A

very large, multi-subunit complex that sits in the double membrane of the nucleus. anchored in place components inserted in the lumenal space

31
Q

how can small molecules leave the nucleus?

A

by diffusion; the nuclear pore is lined with proteins with extended conformations containing phenylalanine-glycine repeats, these help the NPC recognise proteins to assist in transport

32
Q

what are importins and exportins?

A

nuclear transport receptors; these recognise sorting signals on transported molecules and carry them through the pore

33
Q

what is an NLS?

A

nuclear localisation signal, targets a protein for the nucleus. usually consists of one or two stretches of basic residues