Proteins are complex, large molecules that perform a vast array of functions within living organisms. They are fundamental to the structure, function, and regulation of the body’s tissues and organs. Proteins consist of smaller units called amino acids, linked together in long chains, and their specific arrangement dictates their unique three-dimensional shape and biological role.
Early Scientific Insights
Before the formal concept of “protein” emerged, early chemists began to analyze the fundamental components of organic matter. In the late 18th century, Antoine Lavoisier, a French chemist, revolutionized chemistry by introducing quantitative methods. He conducted experiments on elemental analysis, studying substances like waxes, oils, and fats, and determined that organic compounds consistently contained carbon, hydrogen, and oxygen.
Lavoisier’s work laid the groundwork for understanding the basic elemental composition of organic substances, even though the exact proportions of these elements remained a challenge to determine precisely at the time. His rigorous approach shifted chemistry from a qualitative to a quantitative science, providing a foundation for future investigations into the chemical nature of life’s building blocks.
The Naming of Protein
The term “protein” was officially coined in 1838 by the Swedish chemist Jöns Jacob Berzelius. He proposed this name, derived from the Greek word “prota” meaning “primary” or “of prime importance,” due to his belief in the fundamental significance of these substances in biological systems. Berzelius’s suggestion followed the work of Gerardus Johannes Mulder, a Dutch chemist who performed extensive chemical analyses of various organic compounds.
Mulder’s research revealed that many of these substances, despite their different origins, shared a common chemical core and consistently contained nitrogen. He proposed a general formula for this common core, recognizing its widespread presence and importance. This understanding of a shared foundational element, combined with the recognition of their universal occurrence and diverse roles, led Berzelius to formalize the term “protein,” establishing a distinct category for these vital molecules.
Unraveling Composition and Structure
Following the naming, scientists began to unravel the precise composition and intricate structure of proteins. It was established that proteins are long chains made up of about 20 different types of amino acids, linked by what Emil Fischer termed “peptide bonds.” Fischer, a German chemist, significantly advanced this understanding in the late 19th and early 20th centuries by synthesizing short chains of amino acids, known as peptides, and proving the existence of these bonds.
A major breakthrough in understanding protein structure came with Frederick Sanger’s work on insulin in the 1950s. Sanger, a British biochemist, successfully determined the complete amino acid sequence of insulin, demonstrating that proteins have a precise, defined, and unique order of amino acids.
The ultimate revelation of protein structure arrived with the use of X-ray crystallography to determine their three-dimensional shapes. John Kendrew and Max Perutz, working at Cambridge University, pioneered this technique for proteins. Kendrew determined the structure of myoglobin in 1959, while Perutz deciphered the more complex structure of hemoglobin shortly thereafter. Their work revealed how these amino acid chains fold into precise, intricate three-dimensional arrangements, which are essential for their biological functions.
Discovering Biological Functions
As scientists gained a clearer picture of protein composition and structure, their diverse biological functions also became apparent. A significant early insight involved enzymes, which are proteins that act as biological catalysts. Eduard Buchner’s work in 1897 demonstrated that cell-free yeast extracts could carry out fermentation, proving that living cells were not strictly necessary for enzymatic activity and that enzymes could function independently. Further cementing the understanding of enzymes, James Sumner crystallized the enzyme urease in 1926, conclusively showing that enzymes were indeed proteins.
Beyond catalysis, proteins were found to serve as structural components, such as collagen in connective tissues and keratin in hair and nails. Proteins also play roles in transport, with hemoglobin carrying oxygen in the blood, and in immune defense, as antibodies recognize and neutralize foreign invaders. Additionally, proteins function as signaling molecules, transmitting information between cells, and as contractile elements, like actin in muscle movement. These discoveries collectively highlighted why proteins are so fundamental to life.