An organism's genome is the complete set of genetic instructions, passed from one generation to the next. The genome consists of a set of instructions for building each of the components of a living cell or virus.
Germanium has chemical and physical properties similar to those of silicon. It was predicted as an element ("eka-silicon") by Dimitri Mendeleev in 1871 from calculations made during the construction of his periodic table, and it was discovered by Clemens Winkler in 1886.
Glass is a state of matter. It is a solid produced by cooling molten material so that the internal arrangement of atoms, or molecules, remains in a random or disordered state, similar to the arrangement in a liquid.
The term "global warming" refers to an increase in Earth's mean global temperature because a part of Earth's outgoing infrared radiation is retained by several trace gases in the atmosphere whose concentrations have been increasing because of human industrial, commercial, and agricultural activities. These gases have the ability to absorb radiation, leading to the tendency of the atmosphere to create warmer climates than would otherwise be the case.
In a globular protein, the amino acid chain twists and folds in a manner that enhances the protein's solubility in water by placing polar groups of atoms at the protein's surface (where they can participate in attractive interactions with water molecules). This twisting and folding that determine the overall shape of a protein molecule (its tertiary structure) are due largely to the very complex interplay of intramolecular forces that exists among different groups of atoms within the molecule, and to intermolecular forces acting between groups of atoms on the protein and molecules in the protein's immediate surroundings.
Glycolysis is the sequence of enzymatic reactions that oxidize the six-carbon sugar glucose into two three-carbon compounds with the production of a small amount of adenosine triphosphate (ATP). Glycolysis has two basic functions in the cell.
Glycoproteins are proteins that contain covalently attached sugar residues. The hydrophilic and polar characteristics of sugars may dramatically change the chemical characteristics of the protein to which they are attached.
Gold is a soft, malleable yellow metal. If finely divided, it may be black, ruby, or purple.
Green chemistry is also known as environmentally benign chemistry, or sustainable chemistry. Perhaps the most widely accepted definition of green chemistry is the one offered by chemists Paul Anastas and John Warner, who defined green chemistry as the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.
Hafnium was discovered in 1923 by Danish chemist Dirk Coster working together with Hungarian physicist György K. Hevesy.
Hair has no vital function in the human body but provides an outward sign of health and social communication. The history of hair coloring dates from ancient dynasties of Egypt and China where mineral and plant dyes were widely available to cosmeticians.
The halogens are the family of chemical elements that includes fluorine (atomic symbol F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The halogens make up Group VIIA of the Periodic Table of the elements.
Heat is the transfer of energy that results from the difference in temperature between a system and its surroundings. At a molecular level, heat is the transfer of energy that makes use of or stimulates disorderly molecular motion in the surroundings.
Even at a very low level, heavy metal ions can cause serious health effects, including reduced growth and development, cancer, organ damage, nervous system damage, and in extreme cases, death. The most common heavy metal toxins are aluminum, arsenic, cadmium, lead, and mercury.
Helium, a colorless gas at room temperature, is the first element in the noble gas group, and forms few compounds. It is rare in the atmosphere (1 part in 200,000) and recovered on Earth principally by its separation from natural gas obtained in underground wells.
Hemoglobin is an iron-containing protein found in the blood of nearly all vertebrates and many invertebrates. It transports oxygen from the lungs or gills of an animal to the tissues.
Herbicides are chemicals used to destroy unwanted plants (terrestrial or aquatic) called weeds. Herbicides fall into two broad categories: inorganic (e.g., copper sulfate, sodium chlorate, and sodium arsenite) and organic (e.g., chlorophenoxy compounds, dinitrophenols, bipyridyl compounds, carbamates, and amide herbicides).
A member of the lanthanide, or rare earth, series of elements, holmium is a gray, somewhat shiny, soft metal. It is usually found in minerals containing several of the lanthanides.
Hydrogen was first recognized as a gaseous substance in 1766 by English chemist and physicist Henry Cavendish. The abundance of hydrogen in Earth's crust is 1,520 parts per million.
Hydrolases are hydrolytic enzymes, biochemical catalysts that use water to cleave chemical bonds, usually dividing a large molecule into two smaller molecules. Examples of common hydrolases include esterases, proteases, glycosidases, nucleosidases, and lipases.
Josiah Willard Gibbs was born in New Haven, Connecticut, on February 11, 1839, into a family of academics whose connection to higher education dates back to the 1600s. Gibbs entered Yale University (where his father served as librarian) in 1854, graduated in 1858 with distinction in mathematics and Latin, and continued his studies there, in 1863 earning the first Ph.D.
Charles Goodyear was born in New Haven, Connecticut, on December 29, 1800. Goodyear began his work on rubber in 1834, when rubber from Brazilian trees (Hevea brasiliensis) was first being imported to the United States in large quantities.
Fritz Haber, born in Breslau, Prussia (now Wroclaw, Poland), successfully applied physical chemistry to technological problems. In 1918 he won the Nobel Prize in chemistry for his synthesis of ammonia from the elements, an important starting material in the production of fertilizers and explosives.
Although aluminum is now widely used as a structural material, this was not always the case. Common in Earth's crust, aluminum is difficult to win from its ore because it is such a reactive metal.
More so than any other physicist of the twentieth century, Werner Karl Heisenberg challenged our fundamental notions of the surrounding world. It could be argued that as the author of papers on quantum mechanics and the uncertainty principle, he nailed the coffin shut on the deterministic Newtonian version of the universe.
Germain Henri Hess is noted today for two fundamental principles of thermochemistry: the law of constant summation of heat (known simply as Hess's law) and the law of thermoneutrality. These discoveries were remarkable in that they were postulated without any supporting theoretical framework and took place in a field of study almost totally neglected by his contemporaries.
Jaroslav Heyrovský was born on November 20, 1890, in Prague (then part of the Austro-Hungarian Empire), where he also died on March 27, 1967. He began studying chemistry and physics at Prague University in 1909.
The most powerful technique for determining the structure of a chemical compound is x-ray crystallography. In this technique, a beam of x rays is focused on a crystal of a compound.