Question

You’re having a discussion with a colleague who insists that intermediate filaments, IFs, provide very little mechanical strength to cells. How can you rebut this and provide quantitative, experimental evidence to measure the strength of an intermediate filament using microscopy?   

Answer 1

The main function of intermediate filaments:-

• Structural, mechanical strength
• Not directly associated with motility, there are no specific molecular motors associated with IFs
• Cytoplasmic IFs found in multicellular eukaryotic cells.

Intermediate filaments structure and composition:-

• Solid, smooth filament of ~8-10 nm in diameter.
• All IFs have similar domine structure.

Benifits of intermediate filaments strength

• Are able to resist pulling force can sustain tension.
• Can help maintain structural integrity of epithelial tissue.
• Not easily solubilized( important for stable structural molecule)

Experimental evidence:-

​​​​​​Intermediate filaments are not assembled at the ends like(polarized MTs & MF's).

• Stable polymerized keratin(a type of IF in skin epithelial cells) IFs were injected with free keratin subunits, subunits are quickly incorporated into all parts of the IF filament and not at the end.
• Most likely phosphorylation is involved in the stability of polymerize form and I stability of depolymerized form.

Middle rod shaped, alpha helical, 45 NM long.

Globular heads can be more variable in sequence and size.