Microbiology 10: (Shackleton) Intermediate Filaments Flashcards

1
Q

Categories of intermediate filaments (IFs)? Where are they found?

A
Lamins - nuclei
Keratins - Epithelial cells
Vimentin - Fibroblasts
Neurofilaments - Neurons
Desmin - Muscle cells
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2
Q

IF general structure?

A

Conserved structure with a central alpha-helical domain that promotes dimerisation

Head domain - Rod - Tail domain
separated by rod (alpha-helical domain) coiled coils

Dimers can polymerise to form tetramers, eight tetramers to form filaments

filaments NOT POLAR in nature

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3
Q

Characteristics/properties of IFs?

A
  • Filaments are non-polar
  • More stable (less dynamic) than actin, microtubules
  • Bend easily but very difficult to break
  • Have great elastic properties
  • Prominent in cell types subject to mechanical stress e.g. skin, muscle
  • IFs provide cells with tensile strength + resistance to mechanical strain
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4
Q

Describe nuclear lamin function

- how was the function determined?

A

Form a proteinacious meshwork underneath the nuclear envelope - the nuclear lamina

Provides structural support to the nuclear envelope

Organises nuclear contents, including chromatin

Lmna knockout mice showed malformed chromatin organisation, nuclear lamina (showed function)

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5
Q

Describe Inherited disorders caused by Lmna mutation? Why so many?

A

Laminopathies

Emery-Dreifuss muscular dystrophy
- abnormally shaped nuclei susceptible to rupture through weakening of nuclear lamina

Partial lipodystrophy

Hutchinson-Gilford progeria syndrome
- proteins retain farensyl lipid group in mutation -> causes thickened lamina, loss of elastic properties and early cell senescence

Causes so many diseases due to LaminA/C proteins contributing to most nuclear processes (different mutations have different interactions)

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6
Q

Describe keratin structure - how do they interact with desmasomes

A

Formed of heterodimers of acidic and basic/neutral chains

Disulphide bonds cross-link the filaments forming very strong networks
- cysteine comprises 14% of residues in hair keratins

Keratins strengthen epithelia through desmosomes/hemi-desmosomes

  • Connections between neighbouring cells and with the basal lamina
  • (desmin plays similar role in heart muscle)
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7
Q

Mutations in keratin genes result in what?

A

Skin blistering diseases e.g. Epidermolysis bullosa simplex (weakened epithelial links)

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8
Q

What are neurofilaments? Types? Function?

A

Found in neurons - provide tensile strength to axons

3 types
NF-L (Light), NF-M (Medium), NF-H (Heavy)
- NF-L forms heterodimers with the 2 other types

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9
Q

Mutations in neurofilament genes lead to what? Example ?

A

Neurodegenerative disorders

e. g. Charcot-Marie-Tooth disorder
- Peripheral Neuropathy
- Neurofilament disruption leads to peripheral axon degeneration

  • Causes progressive weakening + loss of function
    of some muscles in foot (because longest axons found here)
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