What is Keratin Its Structure Types and Functions in the Human Body
From numerous television commercials of hair oils and shampoos, it has become quite well known that keratin is found in the hair. It can be concluded that keratin is an essential protein for hair growth and development. Scientifically speaking, keratin protein is one of the families of fibrous structural proteins known as the scleroproteins.
In vertebrates like human beings, the variant of keratin protein available is the 𝛼-Keratin. This keratin is an essential structural protein not only for the growth and development of hair but also for making up the scalp, nails, feathers, horns, hooves, calluses, claws, and outer layer of the skin. The keratin protein is also responsible for the protection of epithelial cells from stress or damage.
Keratin Characteristics
Keratin is a structural protein which is extremely insoluble in water and organic solvents. The monomers of keratin protein come together to form bundles of intermediate filaments that are strong and tough. In reptiles, birds, amphibians, and some mammals they create a strong and unmineralized form of epidermal appendages such as hair follicles and sebaceous glands, etc.
Usually keratin in two types: soft and hard. The softer keratin is a primitive form found in all the vertebrates whereas the harder keratin is found in the epidermis of reptiles and birds. Keratin is strong and resists digestion from digestive juices. Owing to this reason, cats regurgitate hairballs as they are unable to digest the hair keratin.
Keratin is subdivided, based on its secondary structure, into two types of keratin: the 𝛼-Keratin and the β-Keratin. They are explained briefly as follows:
𝛼-Keratin: From the given introduction, it is known that 𝛼-Keratin is present in all the vertebrates and is responsible for the formation of hair, nails, feathers, horns, etc. The polypeptide chains under the influence of hydrogen-bonding are helical in this type of keratin.
β-Keratin: On the other hand, another type of keratin, the β-Keratin is found in the nails, claws, and scales of reptiles and in the feathers, claws, and beaks of birds due to its characteristic property of being hard. Sometimes this β-Keratin is also found in the shells of reptiles such as some species of tortoise. In this type of keratin, the polypeptide chains are arranged as parallel sheets.
Another characteristic of the structure of keratin is the composition of amino acids. Depending upon the localization of the keratin molecules in the body, the content of amino acids that make up keratin varies. Especially the cysteine residue is found to vary amongst the different structures of keratin as it is mainly responsible for the stability of the protein. An important part of the keratin structure is the formation of disulfide bridges amongst these cysteine residues. The degree of the disulfide bridge formation varies depending on the region where the keratin is present. For instance, the number of disulfide bridges in hair keratin is less than the number of disulfide bridges in the keratin present in the nails. In many of the keratin treatment of hair keratin the main focus are these disulfide bridges. An example of this includes the chemical-based treatment in which the disulfide bonds are broken in order to provide a straight strand of hair.
Keratin has a filamentous structure formed from the intermediate filaments. The fibers of keratin undergo a series of steps beginning with dimerization, and then further assembling into the tetramers and octamers eventually forming the filaments of unit length. These unit-length filaments are capable of annealing end-to-end into long filaments.
The length of the pure keratin fibers is dependent on the water content in it. Complete hydration of the keratin fibers increases their length by 10% to 12%. This is the reason for the growth of hair keratin and nail keratin.
Keratin Treatment of Hair
Keratin is the building block of the filaments of strands of hair. The amount of hair keratin is indicative of the health of the hair. A decent amount of keratin shows that the hair is healthy. But owing to certain lifestyle habits such as exposure to chlorinated water in swimming pools and other places and certain unavoidable circumstances such as harmful rays from the sun, the health of the hair diminishes with the decrease in the amount of keratin. Because of this many people prefer keratin treatment to keep their hair healthy.
Another reason for the preference of keratin treatment is stylizing of hair according to the needs, and interests of the person. For example, straightening of hair, a very common practice since the 1950s, is one of the most common uses of keratin treatment. There are many commercial products available for helping the consumers for use at home or at the salon. These products include keratin oil, shampoos, and conditioners containing keratin. One of the most common and famous products in this category is the loreal keratin products which are widely used amongst customers. As already disclosed above there are also many chemical keratin treatment techniques also available in the market that are used and applied by the consumers. Another evolving of such treatment techniques is the keratin hair spa which is some of the exclusive centers for keratin treatment. Although the opinions on the best keratin treatment vary from home remedies to professional salon techniques, the consumers are cautioned against repeated utilization in order to avoid hair damage as these can be harmful on regular use.
FAQs on Keratin Structure Properties and Biological Role
1. What is keratin in chemistry?
Keratin is a fibrous structural protein composed mainly of amino acids rich in sulfur, especially cysteine, that forms hair, nails, and the outer layer of skin. Chemically, keratin is a polypeptide made of long chains of amino acids linked by peptide bonds (–CO–NH–). Its structure is stabilized by:
- Disulfide bonds (–S–S–) between cysteine residues
- Hydrogen bonds between peptide backbones
- Hydrophobic interactions between nonpolar side chains
2. What type of protein is keratin?
Keratin is a fibrous protein with a highly ordered secondary structure designed for strength and protection. Unlike globular proteins (such as enzymes), keratin has:
- Long, parallel polypeptide chains
- Repetitive amino acid sequences
- Extensive cross-linking via disulfide bonds
3. What is the chemical composition of keratin?
Keratin is primarily composed of amino acids containing carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). The protein backbone consists of repeating –NH–CH(R)–CO– units formed by peptide bonds. Key chemical features include:
- High levels of cysteine (contains sulfur)
- Formation of disulfide bonds (–S–S–)
- Amide functional groups from peptide linkages
4. Why is keratin rich in cysteine?
Keratin is rich in cysteine because cysteine forms strong disulfide bonds (–S–S–) that increase mechanical strength and stability. When two cysteine residues oxidize, they form a disulfide bridge:
- 2 R–SH → R–S–S–R + 2H+ + 2e−
- Strengthen the protein structure
- Increase rigidity in hair and nails
- Make keratin resistant to chemical and physical stress
5. What is the difference between alpha-keratin and beta-keratin?
The main difference between α-keratin and β-keratin is their secondary structure: alpha-keratin forms helices, while beta-keratin forms sheets.
- α-Keratin: Composed of coiled alpha-helices; found in hair, wool, and skin.
- β-Keratin: Composed of beta-pleated sheets; found in feathers, claws, and reptile scales.
6. How do disulfide bonds affect the properties of keratin?
Disulfide bonds increase the strength, rigidity, and chemical resistance of keratin by covalently linking protein chains. These bonds form between cysteine residues and act as cross-links. Their effects include:
- Higher tensile strength
- Reduced solubility in water
- Greater resistance to heat and chemicals
7. Is keratin a primary, secondary, or tertiary structure protein?
Keratin contains primary, secondary, and tertiary protein structures, with a dominant secondary structure.
- Primary structure: Amino acid sequence linked by peptide bonds.
- Secondary structure: Alpha-helices (α-keratin) or beta-sheets (β-keratin).
- Tertiary structure: Folding stabilized by disulfide bonds and interactions.
8. How is keratin formed in the body?
Keratin is formed by protein synthesis in specialized cells called keratinocytes through transcription and translation of keratin genes. The process involves:
- Transcription of DNA to mRNA in the nucleus
- Translation of mRNA to a polypeptide chain at ribosomes
- Folding into alpha-helices or beta-sheets
- Cross-linking via disulfide bonds
9. Why is keratin insoluble in water?
Keratin is insoluble in water because it has extensive hydrophobic interactions and strong disulfide cross-links that prevent dissolution. Key reasons include:
- Nonpolar amino acid side chains that repel water
- Covalent –S–S– bonds that stabilize structure
- Tightly packed fibrous arrangement
10. What happens to keratin during chemical hair treatments?
During chemical hair treatments, the disulfide bonds in keratin are broken and reformed to change hair shape. For example:
- A reducing agent breaks –S–S– bonds into –SH groups.
- The hair is reshaped mechanically.
- An oxidizing agent reforms new disulfide bonds in the new position.
