Excluding the water present in the human body, about one half of the remaining mass is composed of a class of molecules called proteins. It should therefore be of no surprise that proteins carry out many important biological processes.
At the surfaces of proteins are amino acid residues that interact with water. The amino acids are referred to as hydrophilic amino acids and include arginine, lysine, aspartic acid, and glutamic acid.
There is no task more important to the function of living cells than the synthesis of proteins. Because proteins carry out so many different tasks, the mechanism to synthesize them is intricate.
Protein translation is the process of synthesizing proteins from amino acids. This series of reactions translates the code provided to messenger ribonucleic acid or RNA (mRNA) by deoxyribonucleic acid or DNA into a sequence of amino acids that makes up the active protein molecule.
Quantum chemistry is the application of quantum mechanical principles and equations to the study of molecules. In order to understand matter at its most fundamental level, we must use quantum mechanical models and methods.
Many proteins are made up of a single, continuous polypeptide chain and are thus called monomeric. Other proteins are composed of two or more polypeptide chains called subunits.
Radiation takes many forms, including both electromagnetic waves and sub-nuclear particles. The electromagnetic spectrum consists of light waves ranging in length from very short (10−16 meters, or 3.937 × 10−15 inches) to very long (108 meters, or 621,400 miles).
All matter is potentially damaged when exposed to radiation. This article examines radiation exposure to living systems.
In 1896 Henri Bequerel, a French physicist, was studying the fluorescence of uranium compounds. He placed crystals of potassium uranyl sulfate on top of photographic film wrapped in dark paper and exposed the crystals to sunlight.
Radium is the last of the alkaline earth metals comprising the second column of the Periodic Table. While there are twenty-five known isotopes of radium (only four of which are found naturally), all of them are radioactive.
Radon is a member of the noble gas family and was the first radioactive gas to be discovered. It is colorless, odorless, and chemically inert (like the other noble gases), but it is a highly radioactive α-particle emitter.
In chemistry, there is much interest in how quickly reactant molecules are transformed into product molecules and in the reaction steps or "mechanism" by which the chemical transformation occurs.
Recombinant DNA (rDNA) is made of segments of DNA (polymers of deoxyribonucleotides) from two or more sources. Nature has been recombining DNA in living cells for eons, but humans have only recently discovered the means to carry out this operation in the test tube.
Remains of human settlements through the ages are characterized by garbage. Early human encampments are surrounded by discarded bones, shells, and broken tools and weapons.
A residue is a single molecular unit within a polymer. Residue is thus another term for monomer.
Restriction enzymes (also known as restriction endonucleases) are enzymes that cut double-stranded DNA at very specific recognition sites. They were originally discovered in bacteria that use them to restrict the growth of viruses but are now among the workhorse enzymes of biotechnology and recombinant DNA research.
Retinol, or vitamin A, is a necessary nutrient in all higher animals. It plays an important role in vision, in the maintenance of epithelial cell layers, in spermatogenesis, and in fetal development.
Rhenium was discovered in a sample of gadolinite in 1925 by Walter Noddack, Ida Tacke, and Otto Berg, and was named after the Rhine River. The concentration of rhenium in Earth's crust is on the order of 7 × 10−8 percent.
Rhodium was discovered in 1804 by the English chemist William Wollaston. Its name derives from the Greek word rhodos, meaning rose—the color of solutions containing rhodium salts.
Riboflavin, also known as vitamin B2, gets its name from its sugar alcohol (ribitol), and from its yellow color and its fluorescence under UV light (flavin comes from the Latin word for yellow). Its systematic names are 7,8-dimethyl-10-(D-ribo-2,3,4,5-tetrahydroxypentyl)isoalloxazine and 7,8-dimethyl-10-ribitylisoalloxazine; its formula is C17H20N4O6.
Ribonucleic acid (RNA) is a nucleic acid, like DNA, and is also made up of sugars, phosphates, and nitrogenous bases (or just a base). It contains a ribose sugar, whereas DNA contains a deoxyribose sugar.
Biochemists refer to RNA synthesis as transcription. Transcription is the process of synthesizing ribonucleic acid (RNA).
The Chinese, in the second century B.C.E., were the first to make simple rockets that used gunpowder for fuel. These simple rockets were fireworks that were used for religious ceremonies.
Chandrasekhara Venkata Raman described himself as a "child of nature"; he was indeed a profound student of nature all his life, a keen and resourceful observer of the world around him. In addition to discovering the physical effect that bears his name, he can also be considered the father of modern Indian experimental science.
William Ramsay, the only child of civil engineer and businessman William Ramsay and his wife Catherine, was born on October 2, 1852, in Glasgow, Scotland. Despite the scientific background of his family, he was expected to study for the ministry.
Most great chemists are remembered for their research. Ira Remsen, although he contributed significantly to the research of his time, is one of the few chemists remembered mainly for his teaching and mentorship.
An acknowledged giant of twentieth-century organic chemistry, Robert Robinson authored 700 research papers that continue to influence the way organic chemists think about synthesis, natural products, and reaction mechanisms.
In 1901 Wilhelm Conrad Röntgen (or Roentgen) was the recipient of the first Nobel Prize in physics, awarded to him "in recognition of the extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him." The "remarkable rays" Röntgen called x rays (for want of a better name), but in Germany they very quickly came to be called Röntgen rays. A very shy man, Röntgen declined to give the customary acceptance speech at the awards ceremony.