Keratin
Definition and meaning of Keratin in chemistry.
Keratin is a tough, fibrous structural protein that forms the primary building blocks of hair, nails, horns, feathers, and the outermost layer of human skin. It is highly resistant to physical wear and tear and completely insoluble in water.
In more detail
Keratin is a remarkable family of structural proteins designed by nature to withstand intense mechanical stress and protect delicate underlying tissues. Unlike the globular proteins that function as enzymes or transporters, these proteins assemble into long, extremely durable fibers. The human body produces two main varieties: alpha-keratins, which are found in the hair, nails, and the epidermis of the skin, and beta-keratins, which are much harder and are found in reptile scales and bird feathers.
These proteins are specifically synthesized by specialized cells called keratinocytes. As these cells mature and move toward the surface of the skin, they fill themselves with the fibrous protein and die, creating a tough, waterproof barrier. The incredible physical strength of this biomolecule is derived from its unique chemical structure.
The protein chains contain an exceptionally high concentration of the amino acid cysteine. Cysteine molecules possess sulfur atoms that are capable of bonding with other sulfur atoms on adjacent protein chains. These strong connections are known as disulfide bridges.
Because disulfide bridges are actual covalent chemical bonds, they tightly lock the protein fibers together, making the resulting biological material highly resistant to tearing, stretching, and chemical degradation. The number of disulfide bridges directly determines the rigidity of the biological structure. For instance, the keratin in human hair has fewer sulfur cross-links, rendering it flexible and slightly elastic.
In contrast, the keratin in a rhinoceros horn or a human fingernail contains a massive number of these cross-links, resulting in a hard, rigid structure. The distinct smell of burning hair is caused by the sudden breaking and release of these sulfur compounds. Cosmetic treatments, such as hair perms or chemical straighteners, work by intentionally breaking these disulfide bonds and reforming them in a new shape.
Key facts
| Field | Biochemistry |
|---|---|
| Protein Type | Fibrous structural protein |
| Key Amino Acid | Cysteine |
| Primary Bond | Disulfide bridges (covalent sulfur-sulfur bonds) |
| Properties | Insoluble in water, high tensile strength |
| Locations | Hair, skin, nails, hooves, horns, and feathers |
The waterproof, protective outer layer of your skin is entirely composed of dead cells that are densely packed with rigid keratin fibers.
Frequently asked questions
Why is it completely insoluble in water?
The dense packing of the fibers and the strong covalent cross-links prevent water molecules from penetrating and dissolving the protein structure.
How do hair relaxers work chemically?
They use harsh chemicals to break the strong disulfide bridges within the hair's keratin, allowing the fibers to be physically straightened.
What is the difference between alpha and beta variations?
Alpha variations form helical structures found in mammals, while beta variations form pleated sheets found in harder materials like bird beaks and reptile scales.