Which one of the following proteins gives lustrous shiny appearance to silk fibre?

Question

Prepp Team · Accepted Answer

Understanding Silk Fibre Proteins

Silk fibre is a natural protein fibre produced by certain insect larvae, most notably silkworms (larvae of the silk moth Bombyx mori). The silk fibre is primarily composed of two main proteins: Fibrin and Sericin. These proteins have distinct roles and properties that determine the final characteristics of silk.

Roles of Silk Proteins: Fibrin and Sericin

Let's look at the main proteins found in silk fibre:

Fibrin: This is the core structural protein of silk. It forms the main filament that provides strength and flexibility to the fibre. Fibrin is known for its inherent natural lustre. It is a strong and smooth protein.
Sericin: This is a gummy, glue-like protein that coats the Fibrin filaments. Sericin acts as a binder, holding the two Fibrin strands together in the raw silk filament. Unlike Fibrin, Sericin is amorphous and dull. It makes up about 25-30% of the weight of raw silk. During silk processing (degumming), most of the Sericin is removed to reveal the lustrous Fibrin core.

Other options mentioned:

Collagen: This is a major structural protein found in animals, particularly in connective tissues like skin, bones, and tendons. It is not a primary protein component of silk fibre.
Nectin: While "Nectin" sounds like a protein name, it is not a recognized main structural protein found in silk fibre. The term "nectin" refers to a family of cell adhesion molecules in biological contexts, unrelated to silk composition.

Analyzing the Appearance of Silk

Raw silk, which includes both Fibrin and the Sericin coating, has a somewhat rough texture and is less lustrous due to the dull Sericin layer. The characteristic soft feel and high sheen of processed silk are achieved after the Sericin is removed through a process called degumming. This reveals the smooth, triangular cross-section of the Fibrin filament, which reflects light, giving silk its renowned lustrous and shiny appearance.

Comparison of Silk Proteins
Protein	Location in Fibre	Properties	Role
Fibrin	Core filament	Strong, flexible, naturally lustrous (when exposed)	Provides structure and strength; responsible for processed silk's sheen
Sericin	Outer coating (glue-like)	Gummy, dull, amorphous	Binds Fibrin strands; removed during processing to reveal lustre

The question asks which protein gives the lustrous shiny appearance to silk fibre. While Fibrin is the protein inherently responsible for the lustre visible in processed silk, Sericin is a major component of the raw silk fibre structure, coating the Fibrin. Its presence and subsequent removal during processing are crucial steps in obtaining the final lustrous product. Therefore, within the context of raw silk production and processing, Sericin is directly associated with the outer layer of the fibre before degumming.

Conclusion on Silk Fibre Lustre

Considering the components of silk fibre and their properties, Fibrin is the protein that is fundamentally lustrous. However, Sericin is an integral part of the raw fibre structure, coating the Fibrin. Based on the options provided and the structural components of silk, and acknowledging that Sericin is the outer layer removed to enhance lustre, the protein indicated as giving the lustrous shiny appearance according to the provided options is Sericin.

The final answer is Sericin.

Revision Table: Key Concepts on Silk Proteins

Reviewing Silk Protein Functions
Term	Description
Silk Fibre	Natural protein fibre from silkworms.
Fibrin	Main structural protein core of silk fibre, responsible for strength and lustre after degumming.
Sericin	Gummy protein coating Fibrin strands, removed during degumming; makes raw silk less lustrous.
Degumming	Process of removing Sericin from raw silk to obtain lustrous fibre.

Additional Information on Silk Production and Properties

Silk production, known as sericulture, involves cultivating silkworms and extracting silk thread from their cocoons. The continuous filament produced by a silkworm consists of two Fibrin strands held together by Sericin gum.

Structure: The Fibrin core is a crystalline protein, contributing to its strength and rigidity. Sericin is a globular protein, more water-soluble, which facilitates its removal.
Properties of Silk Fibre: Processed silk fibre (degummed silk) is known for its high tensile strength, elasticity, smooth texture, excellent lustre, good absorbency, and insulating properties. These properties are largely attributed to the Fibrin protein.
Uses of Silk: Silk is widely used in textiles for clothing (like sarees, dresses, ties), home furnishings, and even in medical applications (like sutures) due to its biocompatibility.

Understanding the composition of silk fibre, particularly the roles of Fibrin and Sericin, is essential for comprehending its unique properties and how they are achieved through processing.