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Cells > Mod4 - The Cytoskeleton and Molecular Motors > Flashcards

Mod4 - The Cytoskeleton and Molecular Motors Flashcards

1
Q

In what groups of organisms are the following found - actin microfilaments, microtubules, intermediate filaments?

A

Actin microfilaments = all eukaryotes; MTs = all eukaryotes, Intermediate Filaments = most animals

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2
Q

Describe the structure of microtubules

A

Unbranched cylinders assembled from α/ß tubulin heterodimers (25nm diameter)

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3
Q

Describe the “polar” nature of microtubules

A

“Plus ends” grow rapidly, with ß-tubulin exposed; “minus ends” grow slowly, if at all

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4
Q

How well can spontaneous MT formation occur in a test tube/in a cell?

A

TT: Tubulin + GTP + Mg2+ -> (37C) Microtubules!
Cell: Tubulin concentration too low for polymerisation to occur spontaneously

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5
Q

How do cells speed up MT polymerisation since tubulin concentration is low?

A

They use a template made of gamma-tubulin and other proteins (this is called nucleation)

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6
Q

How does nucleation speed up MT formation?

A

Spontaneous growth involves more unfavourable (slow) steps than growth from a preformed nucleus

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7
Q

Gamma tubulin rings are concentrated on specific structures - name two examples

A

Centromeres and Basal Bodies

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8
Q

Where in the cell are the plus and minus ends of MTs?

A

Plus ends at the periphery; minus ends at the cell centre (centrosome)

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9
Q

Describe the nature/order of growing and shrinking seen in MTs

A

Each MT grows and shrinks independently of its neighbours, and can switch between growing and shrinking (dynamic instability)

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10
Q

Describe the role of GTP in microtubules

A

Tubulin is a GTPase: GDP tubulin cannot polymerise, but GTP tubulin can. In a microtubule, GTP is gradually hydrolysed back to GDP

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11
Q

Describe the effect of the presence/absence of the GTP cap on MT growth

A

If a GTP cap is present, the MT will continue to grow; if the GTP cap is lost, MT will depolymerise; if a new GTP cap forms, the MT will start growing again

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12
Q

What can stabilise microtubules (3 things)?

A

Holding Microtubule-Associated Proteins (MAPs) all along the molecule; binding the drug Taxol; capture of MT plus ends by proteins at the cell cortex

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13
Q

How can MTs be experimentally depolymerised? (2 ways)

A

Putting cells on ice; using drugs that bind free tubulin dimers, preventing new assembly (e.g., Nocodazole, Colcemid, Colchicine)

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14
Q

Describe the structure of actin filaments

A

Thin, flexible, helical filaments, assembled from monomeric actin (7nm diameter)

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15
Q

Describe the polar nature of actin filaments

A

They have a plus end (ATP-bound actin) and a minus end (ADP-bound actin)

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16
Q

Name three natural small molecules which can alter actin polymerisation (and how)

A
  1. Phalloidin - stabilises AFs
  2. Cytochalasin - caps filament ends, preventing actin polymerisation from existing ends
  3. Latrunculin - binds to actin monomers, preventing actin polymerisation
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17
Q

What effect does formin have on actin filaments?

A

It is a Nucleating Protein - promotes polymerisation

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18
Q

What effect does the Arp2/3 complex have on actin filaments?

A

It alters filament length/dynamics

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19
Q

Name 4 types of proteins that alter actin filament organisation

A

Severing, cross-linking, bundling and capping proteins

20
Q

Name two types of proteins that control or drive movement along actin filaments

A

Site-binding protein, motor protein

21
Q

Name the two neuronal MAPs (microtubule-associated proteins) and one non-neuronal one

A

Neuronal: MAP2 and Tau
Non-Neuronal: MAP4

22
Q

Name the type of motor protein associated with actin filaments

A

Myosins

23
Q

What are the two actin-based structures which probe the environment at the leading edge of migrating cells?

A

Lamellipodia and Filopodia

24
Q

What does Arp2/3 complex do in Lamellipodia?

A

Binds to the side of existing actin filaments, causing branching - thus nucleating the assembly of new actin filaments AND preventing disassembly from the minus end

25
Q

What do capping proteins do in migrating cells?

A

Cap the plus ends of actin filaments, thus stabilising them and preventing further growth

26
Q

What proteins are associated with Filopodia, and what do these proteins do? (Note: they are attached to the plasma membrane)

A

Formins - they nucleate actins, allowing actin polymerisation to extend the filopodia

27
Q

How do cell protrusions adhere to the surface during cell migration

A

Focal contacts containing Integrins; Contractile actin bundles attach to focal contacts

28
Q

Which motor protein pulls the rear of the cell forward during migration?

A

Myosin II

29
Q

Name the three types of cytoplasmic (i.e., non-nuclear) intermediate filaments, and which cells they are found in

A

Keratin Filaments (epithelial cells); Vimetntin and vimentin-related IFs e.g., desmin (CT, Muscle) and Neurofilaments (nerve cells)

30
Q

Which types of organisms contain cytoplasmic and nuclear intermediate filaments?

A

Cytoplasmic: all animals except arthropods and hydra
Nuclear: ALL ANIMALS

31
Q

Which disease is caused by mutation in the nuclear lamina?

A

Progeria

32
Q

Describe the first three stages of Intermediate Filament structure assembly

A

alpha-helical region of monomer -> coiled-coil dimer -> staggered tetramer of two coiled-coil dimers

33
Q

Describe the structure of Intermediate Filaments (starting from staggered tetramer)

A

Lateral association of 8 tetramers -> addition of 8 tetramers to growing filament

34
Q

State 3 key distinguishing features of IFs compared to AFs/MTs

A

IFs do not bind nucleotides (GTP/ATP), are more stable (less dynamic) and are not polarised (due to staggering - two dimers face one way, two the other)

35
Q

Name the protein which links Intermediate Filaments with MTs, actin or desmosomes

A

Plectin

36
Q

Which direction do kinesin and dynein family members move in the cell (and which filament do they move along)?

A

Kinesins: towards + end
Dyneins: towards - end
(Of microtubules)

37
Q

How does cytoplasmic dynein transport different kinds of cargo when there is only one main type of dynein?

A

It binds to different adaptor proteins

38
Q

Name the partner complex with which dynein is associated

A

Dynactin

39
Q

Which type of motor proteins move the ER and Golgi within the cell?

A

ER (mainly) moves outward with the help of KINESINS; Golgi moves using cytoplasmic DYNEIN

40
Q

What type of microtubule motion occurs in cilia and flagella?

A

ANOXEMAL BEATING involving parallel sliding (caused by dynein - linker proteins result in bending instead of just sliding)

41
Q

What are the extra set of microtubules in cilia nucleated by?

A

Basal bodies

42
Q

Name the specialised stable microtubule structures found in cilia and flagella

A

Axonemes

43
Q

Describe the structure of myosin II (““muscle myosin””)

A

The myosin II molecule has a long coiled-coil tail, and can assemble into filaments

44
Q

What is the role of desmin in muscle?

A

Desmins form a scaffold to stabilise the z-discs in myosin filaments

45
Q

How does myosin actually cause muscle contraction?

A

It “walks along” actin filaments, bringing the z-discs closer together (shortening the sacromere)

46
Q

In what structures outside of muscles can contractile myosin II be found?

A

Stress fibres, and contractile rings of dividing cells

47
Q

Describe myosin I (structure and function)

A

Only has 1 head, helps reshape plasma membrane by pulling on underlying actin filaments

Cells (8 decks)

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