Natural fiber Keratin is a structural protein located at the hard surfaces in many vertebrates. Keratin has two forms, α-keratin and β-keratin and are used by different classes of animals. The naming convention for proteins follows that for keratin, alpha keratin is helical and beta keratin is sheet like. Alpha keratin is found in mammalian hair, skin, nails, horn and quills, while beta keratin can be found in avian and reptilian species in scales, feathers, and beaks. The two different structures of keratin have dissimilar mechanical properties, as seen in their dissimilar applications. The relative alignment of the keratin fibrils has a
Hair cell They have also improved frequency selectivity (frequency discrimination), which is of particular benefit for humans, because it enabled sophisticated speech and music. Outer hair cells are functional even after cellular stores of ATP are depleted. The effect of this system is to non-linearly amplify quiet sounds more than large ones so that a wide range of sound pressures can be reduced to a much smaller range of hair displacements. This property of amplification is called the cochlear amplifier. The molecular biology of hair cells has seen considerable progress in recent years, with the identification of the motor protein (prestin) that