Starch is the chief storage form of carbohydrate in plants and the most important source of carbohydrate in human nutrition. A starch molecule is a polysaccharide assembled from the simple sugar glucose; it can contain anywhere from five hundred to several hundred thousand glucose molecules joined by covalent bonds into a single structure.
Steel is an alloy of iron with about 1 percent carbon. It may also contain other elements, such as manganese.
Steroids are a family of lipid molecules that includes cholesterol, steroid hormones, and bile salts. These amphipathic molecules (containing both hydrophobic and hydrophilic regions) are derived from two-carbon acetyl-CoA units, whose combination leads to the formation of isoprenoids (five-carbon isoprene molecular units), and finally to the formation of a seventeen-carbon tetracyclic hydrocarbon, the steroid skeleton.
The substances referred to as stimulants are a variety of compounds that excite the central nervous system or alter the body's metabolic activity. Some stimulants enhance alertness and increase energy whereas others affect emotions and oppose psychological depression.
Stoichiometry refers to the ratios of products and reactants in a chemical reaction. It is a fundamental concept in chemistry, and we shall give a more exact description later.
Storage proteins serve as reserves of metal ions and amino acids, which can be mobilized and utilized for the maintenance and growth of organisms. They are particularly prevalent in plant seeds, egg whites, and milk.
Strontium is the thirty-eighth element in the Periodic Table and the sixteenth most abundant element in Earth's crust. It was first recognized by Adair Crawford in 1790, who named the substance "strontianite," after the Scottish town of Strontian where samples were originally obtained.
A substrate is the substance upon which an enzyme acts in an enzymatic reaction. Enzymes are biological catalysts that increase the rate of chemical reactions by decreasing the activation energy required for that reaction.
Sulfa drugs were the first synthetic drugs with widespread antibiotic activity to be put into clinical use. In the 1930s German chemists observed that certain dyes used to stain bacteria stopped microbial growth.
Sulfur has been known since prehistoric times. Because it is flammable, alchemists regarded sulfur as essential to combustion.
Superconductivity, which is defined as the absence of resistance in a conducting material to a continuously flowing electric current, is a special property that a sizable number of substances attain suddenly at very low temperatures. The substances (called superconductors) include elements, alloys, compounds, and nonstoichiometric ceramic materials.
Wolfgang Pauli once stated that "the surface was invented by the devil," illustrating the complexity and difficulty of studying the surfaces of materials. This prompts a fundamental question: What is the surface of a material?
Most people agree that sustainable energy is energy that is derived from a fuel that is renewable or will never run out and that results in minimal environmental impact. Consequently, the fossil fuels coal, oil, and natural gas clearly do not provide sustainable energy.
Over twenty-one million chemical compounds were known as of 2003. Most have been synthesized by chemists; only a small fraction of these are compounds isolated from natural sources.
Tantalum was discovered in 1802 by Swedish chemist Anders Gustav Ekeberg while analyzing Scandinavian minerals. He named the third-row early transition metal after the Greek god Tantalus, the son of Zeus, because the oxide was difficult to dissolve in strong acids.
Two categories of chemical senses (gustation or taste and olfaction or smell) are important for organisms to respond appropriately to their environments. The sensation of taste detects environmental chemicals and may have initially helped organisms distinguish between new sources of food and potential poisons.
The discovery of technetium in 1937 by the Italian scientists Carlo Perrier and Emilio Segré was an important affirmation of the configuration of the Periodic Table. The table had predicted the existence of an element with 43 protons in its nucleus, but no such element had ever been found.
Tellurium was discovered in gold ores by Franz Joseph Müller von Reichenstein, the chief inspector of mines in Transylvania (Romania), in 1782. Tellurium was named, however, by M.
In everyday terms, temperature is a measure of the "hotness" or "coldness" of a substance. More technically, temperature indicates the direction in which energy flows (as heat) when two objects are in thermal contact: energy flows as heat from a high temperature region to a low temperature region.
Teratogen means, in Greek, "monster forming." Teratogens are chemicals that cause abnormalities in embryos. The most well-known is thalidomide, a drug originally designed to combat morning sickness in pregnant women.
In 1787, near Ytterby, Sweden, Swedish army officer Karl Axel Arrhenius discovered a mineral that he named ytterite. In 1794 Finnish chemist Johan Gadolin, working with ytterite, isolated a mixture of oxides (yttria) from which Carl G.
Wendell Stanley shared the Nobel Prize in chemistry in 1946 with John Northrop, awarded to them "for their preparation of enzymes and virus proteins in a pure form," and with James Sumner "for his discovery that enzymes can be crystallized." In 1926 Sumner had crystallized the enzyme urease; in 1930 Northrop had crystallized pepsin; and in 1935 Stanley had crystallized tobacco mosaic virus. Stanley's result and subsequent findings demonstrated that an infectious agent could possess some of the properties of a chemical molecule.
Hermann Staudinger was one of the most influential organic chemists of the twentieth century. His wide-ranging research interests included the investigation of many kinds of molecules, ranging from small organic compounds to large polymers.
John William Strutt was born at Langford Grove in Essex, England, and was the first child of John James Strutt, the second Baron Rayleigh. In 1861 Strutt ventured to Cambridge University where he studied at Trinity College, the same institute attended by Isaac Newton.
James Sumner received the Nobel Prize in chemistry in 1946 (which he shared with John Northrop and Wendell Stanley), "for his discovery that enzymes can be crystallized." In asserting that enzymes were proteins, Sumner had to battle the considerable opposition of European chemists for many years, particularly that of Richard Willstätter's group in Munich, who believed that enzymes belonged to an as yet unknown class of chemical compounds.
Theodor Svedberg was a physical chemist whose work significantly affected the development of biochemistry in the twentieth century. He was born in Flerang, Valbo, in Sweden on August 30, 1884.
Richard Laurence Millington Synge's fascination with biochemistry came into being when he was a young man. In his 1952 Nobel Lecture, he revealed that, at the age of nineteen, after reading Sir Frederick Hopkins's presidential address to the British Association for the Advancement of Science, he suddenly realized "that living things must have wonderfully precise and complicated working parts on the molecular scale, and that biochemists had the best chance of finding out how these are put together and do their work" (Synge, "Applications of Partition Chromatograpy").
Albert Szent-Györgyi was surely one of the most important scientists of the twentieth century. His research interests included vitamins, enzymatic oxidation mechanisms, muscle contraction, and cancer.