Historical Background and Scientific Foundations

Before the early nineteenth century, most chemists accepted the idea that only living organisms could produce biomolecules. Louis Pasteur popularized the principle of vitalism—the theory that some “vital force” present in living things was necessary to make biochemicals. However, in 1828 the German chemist Friedrich Wöhler (1800–1882) accidentally produced the biomolecule urea, a waste product of human metabolism, from the reaction of two different mineral compounds. This proved that the chemical processes within living beings could be understood within the same rules of the larger field of chemistry.

Much of the earliest work in biochemistry dealt with the fermentation of sugar into alcohol. Before yeast was recognized as a living organism, different researchers argued about its role in the process. Some thought it was totally uninvolved, others thought it was merely a catalyst—an agent that causes a chemical reaction but is not involved in the process itself. When Pasteur proved that natural fermentation does not take place without the presence of yeast, many scientists sought to determine how this happens. It was Eduard Buchner (1860–1917), a German chemist who proved that living yeast is not necessary to ferment sugar, but only the enzymes from within the yeast cells, a breakthrough for which he won the 1907 Nobel Prize in chemistry. This seemingly simple discovery led others to investigate the properties of enzymes and other proteins, eventually revealing the structures of these molecules.

Today, most biochemists accept the idea that the first biomolecules formed before any life was even present. In 1953 American chemists Stanley L. Miller (1930–2007) and Harold C. Urey (1893–1981) performed their famous experiment that showed that the chemical and weather conditions of the very young Earth could have produced organic biomolecules from nonliving mineral sources. Starting with water, methane, ammonia, and hydrogen, they added heat and electricity and allowed the experiment to circulate for several days. After a week, some of the simple compounds had formed amino acids, sugars, and lipids. Many of these biochemical units are able to combine to form more complex biopolymers, which could lead to the development of RNA, the genetic code of simple organisms. In other words, the first living things arose from nonliving molecules that now are known as what make up the basic units of life. It should be noted that no one has yet created living cells from an experiment of this type, but much research continues in this area.

The modern study of biochemistry centers around the isolation of new biomolecules from living organisms, learning about their structure and properties, understanding the complex cellular cycles and pathways in which they are used, and developing new uses for them. The four major types of molecules studied by biochemists are carbohydrates, lipids, proteins, and nucleic acids.

Some biomolecules are hybrids of these major classes or their components (e.g., high-density lipoproteins or HDL are hybrids of lipids and proteins, while chondroitin sulfate, a component of cartilage tissue and arthropod exoskeletons, is an amino-sugar chain). Each of these categories is very large, containing a vast number of very different biomolecules. Because of this great diversity, many biochemists specialize in a much smaller class of molecules, or even one particular molecule. Others might work to create better experimental methods or apply others' discoveries in new ways.