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Cell Biology > Cytoskeleton: Intermediate filaments & Microtubules > Flashcards

Cytoskeleton: Intermediate filaments & Microtubules Flashcards

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1
Q

What does the cytoskeleton allow ?

A

Allows shape alteration, internal organisation, motility and mechanical
interaction with environment

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2
Q

What are the 3 main components of cytoskeleton?

A

Intermediate filaments, microtubules and actin filaments

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3
Q

Where is the Cytoskeleton ?

A

Present in bacteria but not as prominent or complex

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4
Q

Functions of Cytoskeleton ?

A
  • Highly dynamic structure
  • Continuously reorganized in response to
    cell shape alteration, cell division and
    environmental changes
  • Aids cell motility (e.g. sperm cells)
  • Controls organelle location and transport of
    molecules between them
  • Directs chromosome segregation during
    mitosis
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5
Q

What are the different protein composition of the 3 types of cytoskeleton ?

A
  • IFs – Fibrous proteins
  • Microtubules – Globular tubulin subunits
  • Actin – Globular actin subunits
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6
Q

What are Intermediate filaments basic properties ?

Keratin and Vimentin

A
  • Ropelike fibers
  • “Intermediate” diameter of - Composed of fibrous proteins
  • Very flexible
  • Provide tensile strength
  • Protect cells against mechanical
    stress (stretching)
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7
Q

What are some more basic properties of intermediate filaments ?

A 
- Toughest and most durable cytoskeletal
component
- Survive concentrated salt solutions and
nonionic detergents
- Extend across cytoplasm and beyond
cell periphery
- Anchored to plasma membrane at cell to cell junctions (desmosomes)
- Found in nucleus (lamina)
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8
Q

What is the structure of the intermediate filaments ?

A
  • Dimers anti-parallel so ends are the same (no structural polarity) and filaments
    associate by noncovalent bonding alone
  • Combined strength of overlapping tetramers along protein provides overall tensile
    strength
  • Central domains homogenous (tight packing), end domains heterogenous
    (interaction specificity in cytoplasm)
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9
Q

What is the function of intermediate filaments ?

A 
- Prominent in cells subject to mechanic
stress e.g. muscles, nerve cell axons,
skin etc
- Spread locally applied forces to prevent
tearing and rupturing
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10
Q

How any of the intermediates are cytoplasmic and nuclear?

A

There are 4 major types

- 3 cytoplasmic and 1 nuclear

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11
Q

Explain intermediate filaments in Keratins ?

A
  • Largest and most diverse group
  • Further subdivided into acidic and basic keratins
  • Composed of keratin filament subunit mixtures
  • Span entire cell diameter, ends anchor to desmosomes on plasma membrane and indirectly connect with IFs on neighbouring cells
  • Also specialised keratin in hair, teeth and nails/claws
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12
Q

Diseases of keratins - epidermolysis bullosa simplex (EBS)

A
  • Rare inherited human genetic disease (1-3/million births)
  • Caused by mutation in keratin gene (K5 or 14 commonly) – produces truncated keratin proteins which fail to assemble correctly into filaments in the epidermis
  • Skin highly sensitive to mechanical stress – blistering, bruising, bleeding, scarring
  • No cure – lifestyle management, pain management, antiseptic washes
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13
Q

Explain Intermediate filaments for Nuclear Lamina?

A
  • Form 2D meshwork structure on inside layer
    of nuclear envelope
  • Constructed from lamin filaments
  • Disassembles and reforms during cell division
    allowing chromosomal duplication
  • Lamin degradation controlled by
    phosphorylation
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14
Q

What is a disease of lamins? and explain ?

A

Progeria
- Rare human genetic diseases (4-8/million births)
- Caused by mutation in lamin A gene – nucleus unstable and
misformed
- Children age prematurely (10 years per year)
- No cure – survival rare beyond 40’s

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15
Q

What are the basic properties of Microtubules ?

A
  • Stiff hollow tubes
  • Radiate from centrosome
  • Rapid assemble/disassembly
  • Key organisers in the cell
  • Form mitotic spindle in mitosis
  • Power mechanical beat of cilia and
    flagella
  • Transport of vesicles, organelles and
    macromolecules
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16
Q

What is the structure of Microtubules ?

A
  • Composed of globular tubulin subunits
  • a-tubulin and b-tubulin dimers form by
    non-covalent bonding
  • Dimers stack to form wall of hollow
    cylindrical tube
  • 13 parallel protofilaments with
    alternating tubulin forms
  • Structural polarity provided by
    asymmetrical ends
  • a-tubulin = -ve end
  • b-tubulin = +ve end
17
Q

What is the relation of centrosomes to microtubules?

A
  • MTs extend from organizing structures
    called centrosomes
  • Control location, number and orientation of
    microtubules
  • Consist of paired centrioles orientated
    perpendicular to each other
  • Hundreds of ring-like structures consisting
    of g-tubulin – serve as start point
    (nucleation site) for new MT
18
Q

Explain the dynamic instability of microtubules ?

A
  • Following nucleation MTs radiate out rapidly in minutes by addition of
    a/b-tubulin dimers to +ve end
  • Can suddenly shrink or disappear through loss of dimers at free +ve
    end - could regrow after shrinking, or start a new MT growth from a gtubulin ring
  • Process of rapid polymerisation and depolymerisation known as
    dynamic instability
19
Q

+ve ends protected from depolymerisation through ?

A

Binding specific

proteins – can bias location of stable MT formation

20
Q

Dynamic instability driven by?

A

Intrinsic capacity of

tubulin dimers to hydrolyse GTP

21
Q

Free tubulin dimers contain?

A

One molecule of

GTP bound to β-tubulin

22
Q

GTP hydrolyzed to GDP upon?

A

Addition of dimer

to growing MT

23
Q

During rapid polymerization, dimers link faster

than?

A

The rate of GTP hydrolysis

24
Q

End of growing MT formed entirely of ?

A

GTPtubulin which forms “GTP-cap”

25
Q

GTP-dimers associate more strongly and tightly

than ?

A

GDP-dimers – promotes polymerisation

26
Q

Drugs can inhibit both ?

A

MT assembly

Colchicine) and disassembly (Taxol

27
Q

Dynamic instability increases for ?

A

Mitotic spindle formation

28
Q

During differentiation MTs ?

A

Stabilised more readily

29
Q

Motor proteins transport?

A

Macromolecules/organelles using MT ‘tracks’ using

small, awkward, jerky steps

30
Q

What is this powered by ?

A

Powered by repeat cycles of ATP hydrolysis

31
Q

Kinesins direct traffic toward?

A

+ve end

32
Q

Dyneins direct traffic toward?

A

–ve end

33
Q

MTs organize and maintain the ?

A

Position of organelles in the cell

34
Q

Kinesins help stretch ?

A

ER out like a tent across the cell

35
Q

Dyneins pull ?

A

Golgi in close towards the nucleus (except in secreting cells!)

36
Q

Spatial arrangement maintained ?

A

During cell growth (drugs can interfere)

37
Q

MTs in cilia and flagella slightly different ?

A

To cytoplasmic MTs

Cell Biology (16 decks)

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