**Proteins in Silk Fibre**

Silk is a natural protein fiber that is primarily composed of two proteins: fibroin and sericin. These proteins are secreted by certain insects and spiders to produce their silk fibers. The composition and arrangement of these proteins give silk its unique properties of strength, durability, and luster.

**Fibroin: The Main Component**

Fibroin is the main structural protein found in silk fibers. It is responsible for providing silk with its strength and elasticity. Fibroin is a long, fibrous protein made up of amino acids, which are the building blocks of proteins. The amino acids found in fibroin include glycine, alanine, and serine, which are arranged in a repetitive sequence. This arrangement gives fibroin its crystalline structure, allowing the silk fiber to be strong and resistant to breaking.

**Sericin: The Coating Protein**

Sericin is another protein present in silk fibers. It acts as a coating or adhesive to hold the fibroin filaments together. Sericin is produced by the silk gland along with fibroin and covers the fibroin filament, forming a protective layer. It is this sericin coating that gives silk its smooth and lustrous appearance. However, sericin is often removed during the processing of silk to enhance its softness and drape.

**Other Proteins and Variations**

In addition to fibroin and sericin, silk fibers may contain small amounts of other proteins, such as seroin and glue-like proteins. These proteins contribute to the overall properties and characteristics of silk.

It is important to mention that the specific proteins and their ratios may vary depending on the insect or spider species that produce the silk. For example, the silk produced by silkworms (Bombyx mori) is primarily composed of fibroin, while the silk produced by spiders contains a higher proportion of sericin.

In conclusion, silk fibers are mainly composed of fibroin and sericin proteins. Fibroin provides strength and elasticity to silk, while sericin acts as a coating or adhesive. The unique composition and arrangement of these proteins contribute to the exceptional properties of silk such as strength, luster, and durability.

Silk is made up of two type of proteins: Fibroin,Sericin. fibrin protein is the protein which form the silk fibres.