Question

Protein in silk thread is:
A. Fibroin
B. Keratin
C. Albumin
D. Globulin

Answer 1

Larvae of silk worms feed voraciously on mulberry leaves and form a cocoon before moulting into an adult silkworm. The cocoon of silk worm is made of silk threads and the silk thread is formed by the silkworm larva through a silk gland which is a modified salivary gland. Silk is a very economical product derived from an insect and its production is an important subject for economic entomologists.

Complete answer:
Option A: The posterior region of the silk gland is involved in the production of fibroin which forms the most of the silk thread. Fibroin is a fibrous protein and forms very strong threads of silk.
So, option A is correct.
Option B: Keratin is usually found in nails, hairs, horns and hoofs of animals and is a hard protein and hence is not the protein found in silk threads.
So, option B is incorrect.
Option C: Albumin is an example of globular proteins while silk is an example of fiber and is essentially made of a fibrous protein.
Hence, option C is incorrect.
Option D: Globulin is also an example of globular protein and hence is not the type of protein found in the threads of silk fiber.
Hence, option D is incorrect.

Hence, Option A Fibroin is the correct answer.

Note:
Silk produced by silkworms consists of two important proteins which are a type of fibrous proteins. They are fibroin and sericin. The fibroin protein is the main structural part of the silk. The polypeptide chain of fibroin is composed of large amounts of glycine which leads to tight packing of fibroin making the silk fiber tough. Moreover, sericin and fibroin contain large amounts of hydrogen bonds in their structure.