Biochemistry is the study of the chemistry of living organisms. Researchers in this area of science study life on a molecular scale. Biochemistry has its roots in biology, chemistry, and physics. It is not clear when biochemistry was first considered a separate field of science, but the synthesis of urea, an organic compound, from non-organic reactants by Friedrick Wöhler in 1828 serves as a convenient benchmark. In 1953, James Watson and Francis Crick made history when they used methods from biology, chemistry, and physics to describe the double helix structure of DNA.
Although biochemistry is a relatively young field of science, its principles have been used by humans for thousands of years. People in ancient China, India and the Mediterranean region employed biochemistry for making bread with yeast, fermenting beer and wine, and treating diseases with plant and animal extracts. However, it wasn't until the early 19th century that people began to examine the chemical properties of life.
Discoveries in the biological sciences and in chemistry and physics from this point in history onward laid the groundwork for the development of biochemistry. In the field of biology, important advances included discoveries about cell structure and function, the laws of genetics, and DNA. From the fields of chemistry and physics, a foundation for biochemistry could be found in the syntheses of organic chemicals, advances in the understanding of metabolic pathways, and the uncovering of the secrets of molecular structure.
Researchers in the biological sciences were interested in describing life from the perspective of cell organization and function. Other researchers sought to apply physical and chemical laws to uncovering how living cells functioned. Both approaches were equally valid, but their combination provided an even more powerful approach.
Biochemistry has evolved rapidly in the fifty years since 1950. The field can now be divided into three general research areas: cellular structure and function, metabolism and energy flow, and storage and transfer of genetic information.
The chemical basis of life rests on the 28 elements that naturally occur in living organisms. Some of these elements are present in large quantities; others exist in very small amounts. The most abundant elements are carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus. Less abundant elements, which are equally necessary for life, include calcium, manganese, iron, and iodine. The elements found in living organisms serve as building blocks for molecules.
Cells are the smallest organized units in living matter that possess all the atributes of life. The molecules that make up living cells associate with one another to create very large molecules, called macromolecules. The four major components from which cells are constructed are proteins, carbohydrates, nucleic acids, and lipids. Proteins are formed when alpha amino acids are linked by peptide bonds. There are twenty common amino acids which combine to form proteins and they have different side groups with certain chemical properties. The sequence in which the amino acids combines determines the properties of the protein and its three-dimensional shape. This causes the surface of each protein to have certain unique features, which are responsible for the activity and function of the protein. The term carbohydrate is used to describe three types of molecules: monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides are simple sugars, while oligo- and polysaccharides are polymers of monosaccharides which vary in length. Carbohydrates have either structural functions (such as cellulose which forms the walls of plant matter) or energy-storage functions. Nucleic acids are polymers of nucleotides, which themselves are base-sugar-phosphate compounds. The shape of nucleic acids is due to the presence of hydrogen bonds between complementary nucleic acid strands. DNA, which is the genetic material of chromosomes, consists of two complementary polynucleotides coiled into a double helix. The relationship between the nucleotide sequence and the protein amino-acid sequence determines the genetic code. The different types of RNA, which are also nucleic acids, have varied functions in the duplication of the genetic code. Lipids, or fats and oils, have low solubility in water. Phospholipids are structural lipids and are the main component of membrane walls. Phospholipids are molecules which contain a portion that is hydrophobic (dislikes water) and a portion which is hydrophilic (likes water). The hydrophobic parts of two layer of molecules (phospholipid bilayer) form the center of the membrane wall. Water-soluble matter cannot pass through the phospholipid bilayer unless transported by a protein. Proteins present on or in the phospholipid bilayer also catalyze many other important reactions. Exploring the chemical properties of the cell membrane's components can reveal how the membrane accomplishes its tasks. For example, in 1943, Hans Adolf Krebs was largely responsible for the formulation of the citric acid or Krebs cycle. This cycle describes a principal way in which the oxidation of carbohydrates to water and carbon dioxide is carried out with the production of a number of high-energy molecules for each molecule of carbon dioxide that is formed.
There are many other structures associated with cells in addition to the cell membrane. The interior of a cell contains structures called organelles that can be compared to the organs in a body. The organelles handle processes such as metabolism and energy flow. When the cell absorbs nutrients, chemical processes come into play that allow the cell to use these nutrients to support life.
Explorations in the three areas of biochemistry have lead to advances in health, medicine, and nutrition. For example, our need for vitamins is due to the fact that they function as coenzymes in many metabolic processes. As a result, diseases such as diabetes, sickle cell disease, and cystic fibrosis are now known to be caused by problems at the molecular level. This knowledge has lead to therapies that can help people with these diseases. Further explorations may help fight diseases such as AIDS, cancer, and Alzheimer's disease.
Another advancement that has been fueled by biochemical studies is recombinant DNA technology. This technology forms the foundation for the development of plants that can resist disease and contain more nutrients, and for creating new drugs that will aid in the fight against disease. Biochemistry also helps advance the field of biotechnology in which cells, organelles, and biological processes can be used in a variety of ways from creating medicines to cleaning up oil spills and toxic wastes.
Researchers today continue to explore life on the molecular level. Their discoveries pave the way for understanding diseases and finding cures, improving nutrition, and advancing the frontiers of other fields such as biotechnology and molecular biology.
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