Yes, some doors do have a metal coating. Metal-coated doors are especially common in commercial and industrial settings for their durability, security, and fire-resistance qualities. The coating could be made of various metals, including steel, aluminum, or even a zinc-alloy for added protection against corrosion. In residential settings, metal-coated doors are often used for entry or security doors, given their robustness and ability to withstand harsh weather conditions. The metal coating not only enhances the door's strength and longevity but can also contribute to its aesthetic appeal, with finishes ranging from sleek and modern to textured for a more traditional appearance. Moreover, the metal coating can be an integral part of the door's structure, offering a higher level of security and energy efficiency by providing better insulation than wood or fiberglass doors.

Cleaning matt emulsion painted walls involves gentle care to avoid damaging the paintwork. Start by dusting the walls with a soft brush or microfiber cloth to remove surface dust. For marks or stains, use a soft, lightly dampened sponge with water, being careful not to oversaturate the wall as excess water can damage the paint finish. For more stubborn stains, a mild detergent can be added to the water, testing on an inconspicuous area first to ensure it doesn't affect the paintwork. Avoid abrasive materials or harsh chemicals which can strip the paint. Rinse the area with a clean, damp cloth afterwards and pat dry with a towel to prevent watermarks. Always patch-test when trying a new cleaning solution.

An amino acid, the building block of proteins, is comprised of an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a unique side chain (R group) bound to a central carbon atom (alpha carbon). The properties and identity of the amino acid are determined largely by the side chain. In the formation of proteins, amino acids are linked by peptide bonds through a dehydration synthesis reaction, where the carboxyl group of one amino acid binds to the amino group of another. Additionally, amino acids can bind to various other molecules in biochemical pathways, serving as substrates or intermediates in metabolism, signaling, and regulatory functions. The specific binding interactions between amino acids and other molecules underlie the vast functionality and specificity seen in biological processes and structures.