Proteins can be broadly categorized into two main structural types: fibrous and globular proteins. This summary focuses on fibrous proteins, which are characterized by their relative insolubility in water and their arrangement in long, linear strands or sheets. Typically, fibrous proteins exhibit only one type of secondary structure, either alpha helices or beta sheets, leading to a simpler tertiary structure. Their primary role is structural, providing support, shape, and protection in various biological contexts.
Three notable examples of fibrous proteins include alpha keratin, collagen, and silk fibroin. Alpha keratin is a mammalian protein found in hair, skin, and nails, predominantly composed of alpha helices. In its structure, two alpha helices coil around each other to form a coiled coil motif, which further aggregates into protofilaments and ultimately forms alpha keratin filaments.
Collagen, another essential fibrous protein, is integral to connective tissues such as cartilage, tendons, and bones. Unlike alpha keratin, collagen consists of three intertwined polypeptide chains that do not form alpha helices but instead have turns that allow them to twist together. This structure contributes to its strength and stability in various tissues.
Silk fibroin, produced by insects like spiders, is a classic example of a protein featuring beta sheets. The silk fibroin structure is characterized by layers of antiparallel beta sheets that are hydrogen-bonded together, providing remarkable tensile strength and flexibility, which is crucial for the functionality of spider webs.
Understanding these fibrous proteins highlights their importance in biological systems, showcasing how their unique structures correlate with their specific functions in providing support and protection.
