A Level Biology Practice Exam

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What defines fibrous proteins?

Proteins that are soluble in water
Short-chain, flexible proteins
Insoluble, structural proteins
Proteins involved in metabolic reactions

The correct answer is: Insoluble, structural proteins

Fibrous proteins are characterized by their structural role in organisms. These proteins are typically insoluble in water, which allows them to form strong, stable structures that provide support and strength to cells and tissues. For instance, keratin in hair, collagen in connective tissues, and silk fibroin in spider silk are all examples of fibrous proteins. Their elongated, chain-like structure contributes to their mechanical properties, making them suitable for their primary function in providing strength and support, as opposed to being involved in metabolic reactions or being soluble in water. This structural integrity is vital for maintaining the shape and function of cells and tissues in living organisms.