Mention the types and functions of intermediate filaments

Intermediate filaments (IFs) are one of the three major components of the cytoskeleton, along with microtubules and microfilaments. These filaments are made up of fibrous polypeptides and are about 10 nm in diameter, which is intermediate between actin filaments (thinner) and microtubules (thicker). They mainly provide mechanical strength and help maintain the shape of the cell. Based on the types of proteins (polypeptides) that form them, intermediate filaments are classified into five major types (according to traditional classification). However, based on new research, a sixth type has also been added recently.

Type I: Acidic Keratins

These are found in epithelial cells and are rich in acidic amino acids. They always form heterodimers with type II keratins to build stable filaments.

Function: Provide mechanical support to epithelial tissues and help in forming hair, nails and skin.

Type II: Basic Keratins

These are also found in epithelial cells but are basic in nature. They pair with type I keratins to form heterodimers.

Function: Together with type I keratins, they maintain cell shape and resist mechanical stress in epithelial cells.

Type III: Vimentin-like Filaments

This group includes vimentin (in mesenchymal cells), desmin (in muscle cells), glial fibrillary acidic protein or GFAP (in astrocytes), peripherin (in peripheral neurons) and syncoilin (also in muscle cells).

Function: These filaments anchor organelles like the nucleus and maintain cellular integrity and positioning.

Type IV: Neurofilaments

These are mainly found in neurons and include neurofilament proteins (NF-L, NF-M, NF-H), α-internexin, nestin and synemin.

Function: Provide structural support to axons and maintain their diameter which helps in nerve signal transmission.

Type V: Nuclear Lamins

This group includes Lamin A, Lamin C, Lamin B1 and Lamin B2, which form a mesh-like layer called the nuclear lamina beneath the inner nuclear membrane.

Function: Provide structural support to the nucleus and regulate important nuclear activities like DNA replication and RNA transcription.

Note (About Sixth Type):

Recent research has identified Nestin (previously grouped under Type IV) as being significantly different in function and structure. It is now classified under a new sixth type of intermediate filaments because of its development-specific expression in neural stem cells and its highly dynamic behavior, which differs from other stable neurofilaments.
Based on the types of proteins (polypeptides) that form them, intermediate filaments are classified into five major types (according to traditional classification). However, based on new research, a sixth type has also been added recently.








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