Intermediate Filaments Flashcards
What are intermediate filaments?
Have a diameter of about 8-12 nm, making them intermediate in size between microtubules and microfilaments. They are the most stable and the least soluble constituents of the cytoskeleton. They likely serve as a scaffold to support the entire cytoskeleton framework
What is an abundant intermediate filament protein?
Keratin, an important component of structures like hair, claws, and fingernails
What makes class I of intermediate filament proteins?
Acidic keratins
Function: mechanical strength
What makes class II of intermediate filament proteins?
Basic or neutral keratins
Function: mechanical strength
KEY
Proteins of classes I an II make up the tonofilaments found in epithelial surfaces covering the body and lining the cavities
What makes class III of intermediate filament proteins?
Includes vimentin (connective tissue), desmin (muscle cells) and glial fibrillary acidic (GFA) protein (glial cells)
Function: maintenance of cell shape
What makes class IV of intermediate filament proteins?
Neurofilament (NF) proteins
Function: axon strength; determines axon size
What makes class V of intermediate filament proteins?
Includes the nuclear lamins A, B, and C
Function: form a nuclear scaffold/network to give shape to the nucleus
What makes class VI of intermediate filament proteins?
Nestin which make up neurofilaments in the nerve cells of embryos
Function: unknown
How do intermediate filaments assemble from fibrous proteins?
(a) The starting point for assembly is a pair of intermediate filament (IF) polypeptides. The central domains of the two polypeptides twist around each other, with their N- and C-terminal ends aligned. (b) Two dimers align laterally to form a tetrameric protofilament. (c) Protofilaments assemble into larger filaments by end-to-end and side-to-side alignment. (d) A fully assembled IF is thought to be eight protofilaments thick at any point.
What are some properties of IFs?
They are elastic and can withstand tensile forces. They are not static structures; they are dynamically transported and remodeled.
How does the nuclear lamina work?
The nuclear lamina, on the inner surface of the nuclear envelope is composed of three separate IF proteins (nuclear lamins A, B, and C). These lamins become phosphorylated and disassemble as a part of nuclear envelope breakdown at the onset of mitosis. After mitosis, lamin phosphatases remove the phosphate groups, allowing the nuclear envelope to reform.
What are plakins?
They are linker proteins that connect intermediate filaments, microfilaments, and microtubules
