<P> Alpha - keratin, or α - keratin, is a type of keratin found in mammals . This protein is the primary component in hairs, horns, nails and the epidermis layer of the skin . α - keratin is a fibrous structural protein, meaning it is made up of amino acids that form a repeating secondary structure . The secondary structure of α - keratin is very similar to that of a traditional protein α - helix and forms a coiled coil . Due to its tightly wound structure, it can function as one of the strongest biological materials and has various uses in mammals, from predatory claws to hair for warmth . α - keratin is synthesized through protein biosynthesis, utilizing transcription and translation, but as the cell matures and is full of α - keratin, it dies, creating a strong non-vascular unit of keratinized tissue . </P> <P> α - keratin is a polypeptide chain, typically high in alanine, leucine, arginine, and cysteine, that forms a right - handed α - helix . Two of these polypeptide chains twist together to form a left - handed helical structure known as a coiled coil . These coiled coil dimers, approximately 45 nm long, are bonded together with disulfide bonds, utilizing the many cysteine amino acids found in α - keratins . The dimers then align, their termini bonding with the termini of other dimers, and two of these new chains bond length-wise, all through disulfide bonds, to form a protofilament . Two protofilaments aggregate to form a protofibril, and four protofibrils polymerize to form the intermediate filament (IF). The IF is the basic subunit of α - keratins . These IFs are able to condense into a super-coil formation of about 7 nm in diameter, and can be type I, acidic, or type II, basic . The IFs are finally embedded in a keratin matrix that either is high in cysteine or glycine, tyrosine and phenylalanine residues . The different types, alignments, and matrices of these IFs account for the large variation in α - keratin structures found in mammals . </P> <P> α - keratin synthesis begins near focal adhesions on the cell membrane . There, the keratin filament precursors go thorough a process known as nucleation, where the keratin precursors of dimers and filaments elongate, fuse, and bundles together . As this synthesis is occurring, the keratin filament precursors are transported by actin fibers in the cell towards the nucleus . There, the alpha - keratin intermediate filaments will collect and form networks of structure dictated by the use of the keratin cell as the nucleus simultaneously degrades . However, if necessary, instead of continuing to grow, the keratin complex will disassemble into non-filamentous keratin precursors that can diffuse throughout the cell cytoplasm . These keratin filaments will be able to be used in future keratin synthesis, either to re-organize the final structure or create a different keratin complex . When the cell has been filled with the correct keratin and structured correctly, it undergoes keratin stabilization and dies, a form of programmed cell death . This results in a fully matured, non-vascular keratin cell . These fully matured, or cornified, alpha - keratin cells are the main components of hair, the outer layer of nails and horns, and the epidermis layer of the skin . </P>

Alpha keratin is a protein present in which of the following things