optyka: Zinc

Evidence: 100 • authority: 72

Zinc is a chemical element; it has the symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny blue whitish appearance when surface oxidation is removed. It is the first element in group 12 (IIB) of the periodic table. Zinc is the 24th most abundant element in Earth's crust, with an average concentration of 70 grams per ton. Zinc also has five stable isotopes; the most abundant of which, zinc-64, comprises nearly half of zinc's total abundance. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. The most common zinc ore is sphalerite (…

Evidence: 56 • authority: 72

Iron is a chemical element; it has symbol Fe (from Latin ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most abundant element in the Earth's crust. In its metallic state it was mainly deposited by meteorites. Extracting usable metal from iron ores requires kilns or furnaces capable of reaching 1,500 °C (2,730 °F), about 500 °C (900 °F) higher than that required to smelt copper. Humans started to master that process in Eurasia during the 2nd millennium BC and the use of iron tools and weapons began to disp…

Evidence: 49 • authority: 72

Arsenic is a chemical element; it has the symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is notoriously toxic. It occurs naturally in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. It has various allotropes, but only the grey form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is also a common n-type dopant in semiconductor electronic devices, and a component of the III–V compound semiconductor gal…

Evidence: 43 • authority: 92

Iron and Other Metal Ions in Human Health and Disease.. Iron is the most abundant trace element, driving both the commonest deficiency and ferroptosis. This review takes iron as the central theme and extends to copper, zinc, and calcium, spanning physiological functions, pathological mechanisms, risk factors, diagnostics, and therapeutics. We classify these ions into redox-active (iron, copper), which engage in catalytic electron transfer, and redox-inert (zinc, calcium), which serve structural and signaling roles without redox cycling. Iron deficiency remains the global leading micronutrient deficit, whereas iron overload triggers ferroptosis-mediated organ damage. Copper deficiency manife…

Evidence: 43 • authority: 72

Sulfur, also spelled as sulphur, is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with the chemical formula S8. Elemental sulfur is a bright yellow, crystalline solid at room temperature. Sulfur is the tenth most abundant element by mass in the universe and the fifth most common on Earth. Though sometimes found in pure, native form, sulfur on Earth usually occurs as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, and ancient Egypt. Historically and i…

Evidence: 37 • authority: 92

An Investigation of Heavy Metal Accumulation in Liver and Kidney Tissues of the European Hare (<i>Lepus europaeus</i> P.) in Samples Originating from Intensive Agricultural Environments in Hungary.. The aim of this study was to evaluate the concentrations of 17 heavy metals measured in the liver and kidney tissues of the European brown hare ( Lepus europaeus ) as a function of age, sex, organ type, and sampling area. In addition, we assessed the relationships between trace element profiles and reproductive parameters and highlighted their potential relevance from a food-safety perspective. Age-related comparisons revealed significantly higher concentrations of Ti, Fe, Cd, and Hg…

Evidence: — • authority: 72

Zinc is an essential element for all known forms of life. In humans, zinc is required for the function of over 300 enzymes and 1000 transcription factors, and is stored and transferred in metallothioneins. It is the second most abundant trace metal in humans after iron. It is the only metal which appears in all enzyme classes. In proteins, zinc ions are often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult. Roughly 2–4 grams of zinc are distributed throughout the human body. Most zinc is in the brain, musc…

Evidence: — • authority: 72

A holoprotein or conjugated protein is an apoprotein combined with its prosthetic group. Some enzymes do not need additional components to show full activity. Others require non-protein molecules called cofactors to be bound for activity. Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds (e.g., flavin and heme). Organic cofactors can be either coenzymes, which are released from the enzyme's active site during the reaction, or prosthetic groups, which are tightly bound to an enzyme. Organic prosthetic groups can be covalently bound (e.g., biotin in enzymes such as pyruvate carboxylase). An example of an enzyme that contains a cofactor is carbo…

Evidence: — • authority: 72

A restriction enzyme, restriction endonuclease, REase, ENase or restrictase is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class of the broader endonuclease group of enzymes. Restriction enzymes are commonly classified into five types, which differ in their structure and whether they cut their DNA substrate at their recognition site, or if the recognition and cleavage sites are separate from one another. To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix. These enzymes are found in bacteria and…

Evidence: — • authority: 72

An enzyme is a biological macromolecule, usually a protein, that acts as a biological catalyst, accelerating chemical reactions without being consumed in the process. The molecules on which enzymes act are called substrates, which are converted into products. Nearly all metabolic processes within a cell depend on enzyme catalysis to occur at biologically relevant rates. A metabolic pathway is typically composed of a series of enzyme-catalyzed steps. The study of enzymes is known as enzymology, and a related field focuses on pseudoenzymes—proteins that have lost catalytic activity but may retain regulatory or scaffolding functions, often indicated by alterations in their amino acid sequences…

Evidence: — • authority: 72

A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's role as a catalyst. Cofactors can be considered "helper molecules" that assist in biochemical transformations. The rates at which these happen are characterized in an area of study called enzyme kinetics. Cofactors typically differ from ligands in that they often derive their function by remaining bound. Cofactors can be classified into two types: inorganic ions and complex organic molecules called coenzymes. Coenzymes are mainly derived from vitamins and other organic essential nutrients in small amounts (some definitions limit the use of the term "cofactor" for inorganic substances; both types a…

Evidence: — • authority: 72

Silver is a chemical element; it has symbol Ag (from Latin argentum) and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity and reflectivity of any metal. Silver is found in the Earth's crust in the pure, free elemental form ("native silver"), as an alloy with gold (electrum) and other metals, and in minerals such as acanthite, argentite and chlorargyrite. Most silver is recovered as a byproduct of lead–zinc, copper and gold mining and refining. Silver has long been valued as a precious metal and coinage metal. It is one of the seven metals of antiquity, and has had an enduring role in monetary systems, jewellery…