page_title: Intermediate filament
section_title: Types I and II – acidic and basic keratins
hierarchical_section_title: Intermediate filament / Types / Types I and II – acidic and basic keratins
caption_attribution_description: English: Cultured MDCK en:wikipedia:epithelial cells were stained for en:wikipedia:keratin, desmoplakin, and en:wikipedia:DNA. The stained cells were visualized by scanning laser confocal microscopy. The image shows how keratin cytoskeletal filaments are concentrated around the edge of the cells and merge into the desmoplakin which is located at en:wikipedia:desmosomes of the surface membrane. The network of keratin to desmosome to keratin linking the cells of an epithelial sheet is what holds together tissues like skin. Slovenščina: Celice epitelija, obarvane za keratin, dezmoplakin in DNK.
context_page_description: Intermediate filaments are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
  Intermediate filaments are composed of a family of related proteins sharing common structural and sequence features. Initially designated 'intermediate' because their average diameter is between those of narrower microfilaments and wider myosin filaments found in muscle cells, the diameter of intermediate filaments is now commonly compared to actin microfilaments and microtubules. Animal intermediate filaments are subcategorized into six types based on similarities in amino acid sequence and protein structure. Most types are cytoplasmic, but one type, Type V is a nuclear lamin. Unlike microtubules, IF distribution in cells show no good correlation with the distribution of either mitochondria or endoplasmic reticulum.
context_section_description: These proteins are the most diverse among IFs and constitute type I (acidic) and type II (basic) IF proteins. The many isoforms are divided in two groups: 
  epithelial keratins (about 20) in epithelial cells (image to right)
  trichocytic keratins (about 13) (hair keratins), which make up hair, nails, horns and reptilian scales.
  Regardless of the group, keratins are either acidic or basic. Acidic and basic keratins bind each other to form acidic-basic heterodimers and these heterodimers then associate to make a keratin filament.
caption: Keratin intermediate filaments (stained red) around epithelial cells.
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