Question

Silk contains a protein known as
A. Fibroin
B. Casein
C. Sericin
D. Both A and C

Answer 1

Hint: Silk is a secretion obtained from the silkworm. These secretions come from a silk gland which secretes two materials:- long silk thread and the other product is a gluing material which binds all the silk fibers together.
Complete step-by-step answer: Silk is a natural fiber obtained from Bombyx mori. It majorly feeds on mulberry leaves and produces fine-quality silk yarn. Silk is a natural animal protein which is made up of two proteins- 70% fibroin and 30% of sericin.70% fibroin forms the silk filament which is actually the lustrous silk and sericin, the remaining 30% of the protein fiber is responsible for keeping all the silk filaments together.
Fibroin is a long chain of amino acids such as Gly-Ser-Gly-Ala-Gly-Ala. It is a very delicate layer and hence needs to be protected. Fibroin is protected by the sticky outer coating of the protein sericin. It is a sticky layer that helps in the formation of intramolecular and intermolecular hydrogen bonding between the amino acids of the fibroin protein. These intramolecular and intermolecular hydrogen bonding which are formed makes the silk strand highly tensile and helps in keeping the silk fibers held together.
Therefore, the correct answer for the above question is option D- Both A and C.
Note: Sericulture is the method of rearing silkworms for the production of silk. The silk is secreted by the mouth of the insect and is proteinaceous in nature. Silk is composed of fibroin and sericin. Casein is the milk protein which is an amorphous white solid, which is colorless and odorless.