什麼是蛋白質

為數眾多的有機化合物，生物化學作用所需的複雜氨基酸聚合物。蛋白質中出現的氨基酸共有二十種，數百個到數千個單位串連起來。有效的蛋白質具有三層重要結構：一級結構（氨基酸序列）由基因決定；二級結構（幾何形狀，通常是螺旋）由氨基酸之間或內部共價鍵的角度來決定；三級結構（環狀或摺疊的整體形狀）由氫鍵與氨基酸側鏈來決定。三級結構具有突起、裂縫或囊穴的球形或片狀，掌握活動的關鍵。蛋白質有單純蛋白質（僅含氨基酸）與接合蛋白質（參閱conjugation），接合物件通常是飲食中少量需求的維生素或金屬。血紅蛋白是接合蛋白質。蛋白質會與醣類（醣蛋白）、磷（磷蛋白）或硫（硫蛋白）共價連結。構造上的蛋白質是膠原蛋白與角蛋白。幾乎都是蛋白質。生物其他的活性蛋白質包括激素（如胰島素、促腎上腺皮質激素、生長激素）；輸送蛋白質攜帶物質通過細胞膜或到身體不同的部位；還有抗體。蛋白質在工業上有黏著劑、塑膠與纖維等用途，不過大多還是用於食品。

protein

Any of numerous organic compounds, complex polymers of amino acids needed for biochemical processes. Twenty different amino acids can occur in proteins, in chains of hundreds to thousands of units. An active protein has three important levels of structure: primary (the amino acid sequence), determined by the genes; secondary (the geometric shape, often a helix), determined by the angles of the covalent bonds between (peptide bonds) and within amino acids; and tertiary (the looped and folded overall shape), determined by the hydrogen bonds (see hydrogen bonding) between amino-acid side chains. The tertiary structure, globular or sheetlike with ridges, crevices, or pockets, holds the key to an enzyme's activity. Some proteins are simple (amino acids only), some conjugated (see conjugation) to other groups, often vitamins or metals needed in tiny amounts in the diet. Hemoglobin is a conjugated protein. Proteins may be covalently linked to sugars (glyco-proteins), phosphorus (phospho-proteins), or sulfur (sulfo-proteins). Structural proteins include collagen and keratin. Almost all enzymes are proteins. Other biologically active proteins include hormones (e.g., insulin, ACTH, growth hormone); transport proteins, which carry substances across membranes or to different parts of the body; and antibodies. Proteins have industrial uses in adhesives, plastics, and fibers, but most uses are in foods.