Final answer:
Keratin-containing intermediate filaments are tethered to desmosomes and plasma membrane structures, providing tensile strength to cells and tissues, maintaining cell shape, and functioning in cell-to-cell adhesion.
Step-by-step explanation:
Keratin is a fibrous protein that forms intermediate filaments (IFs), which are one of the three main components of the cytoskeleton in cells. These intermediate filaments are predominant in epithelial cells and are tethered to desmosomes, which are specialized structures that function in cell-to-cell adhesion, providing tensile strength to tissues.
Keratin-containing IFs are also linked to the plasma membrane in epithelial cells and muscle cells, where they contribute to maintaining cell shape and transmitting forces during muscle contractions.
Additionally, keratin increases the rigidity of cells and tissues by forming disulfide bonds between cysteine residues in alpha-helices, which confer an elastic nature to keratin, enabling it to return to its original position when tension is released. Keratins are synthesized by keratinocytes in the stratum spinosum of the skin, where they release a water-repelling glycolipid as part of their function to form a barrier.