A base pair is a unit consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA. Dictated by specific hydrogen bonding patterns, Watson–Crick base pairs allow the DNA helix to maintain a regular helical structure, subtly dependent on its nucleotide sequence; the complementary nature of this based-paired structure provides a redundant copy of the genetic information encoded within each strand of DNA. The regular structure and data redundancy provided by the DNA double helix make DNA well suited to the storage of genetic information, while base-pairing between DNA and incoming nucleotides provides the mechanism through which DNA polymerase replicates DNA and RNA polymerase transcribes DNA into RNA. Many DNA-binding proteins can recognize specific base-pairing patterns that identify particular regulatory regions of genes. Intramolecular base pairs can occur within single-stranded nucleic acids.
This is important in RNA molecules, where Watson–Crick base pairs permit the formation of short double-stranded helices, a wide variety of non-Watson–Crick interactions allow RNAs to fold into a vast range of specific three-dimensional structures. In addition, base-pairing between transfer RNA and messenger RNA forms the basis for the molecular recognition events that result in the nucleotide sequence of mRNA becoming translated into the amino acid sequence of proteins via the genetic code; the size of an individual gene or an organism's entire genome is measured in base pairs because DNA is double-stranded. Hence, the number of total base pairs is equal to the number of nucleotides in one of the strands; the haploid human genome is estimated to be about 3.2 billion bases long and to contain 20,000–25,000 distinct protein-coding genes. A kilobase is a unit of measurement in molecular biology equal to 1000 base pairs of DNA or RNA; the total amount of related DNA base pairs on Earth is estimated at 5.0×1037 and weighs 50 billion tonnes.
In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC. Hydrogen bonding is the chemical interaction. Appropriate geometrical correspondence of hydrogen bond donors and acceptors allows only the "right" pairs to form stably. DNA with high GC-content is more stable than DNA with low GC-content. But, contrary to popular belief, the hydrogen bonds do not stabilize the DNA significantly; the larger nucleobases and guanine, are members of a class of double-ringed chemical structures called purines. Purines are complementary only with pyrimidines: pyrimidine-pyrimidine pairings are energetically unfavorable because the molecules are too far apart for hydrogen bonding to be established. Purine-pyrimidine base-pairing of AT or GC or UA results in proper duplex structure; the only other purine-pyrimidine pairings would be AC and GT and UG. The GU pairing, with two hydrogen bonds, does occur often in RNA. Paired DNA and RNA molecules are comparatively stable at room temperature, but the two nucleotide strands will separate above a melting point, determined by the length of the molecules, the extent of mispairing, the GC content.
Higher GC content results in higher melting temperatures. On the converse, regions of a genome that need to separate — for example, the promoter regions for often-transcribed genes — are comparatively GC-poor. GC content and melting temperature must be taken into account when designing primers for PCR reactions; the following DNA sequences illustrate pair double-stranded patterns. By convention, the top strand is written from the 5' end to the 3' end. A base-paired DNA sequence: ATCGATTGAGCTCTAGCG TAGCTAACTCGAGATCGCThe corresponding RNA sequence, in which uracil is substituted for thymine in the RNA strand: AUCGAUUGAGCUCUAGCG UAGCUAACUCGAGAUCGC Chemical analogs of nucleotides can take the place of proper nucleotides and establish non-canonical base-pairing, leading to errors in DNA replication and DNA transcription; this is due to their isosteric chemistry. One common mutagenic base analog is 5-bromouracil, which resembles thymine but can base-pair to guanine in its enol form. Other chemicals, known as DNA intercalators, fit into the gap between adjacent bases on a single strand and induce frameshift mutations by "masquerading" as a base, causing the DNA replication machinery to skip or insert additional nucleotides at the intercalated site.
Most intercalators are known or suspected carcinogens. Examples include ethidium acridine. An unnatural base pair is a designed subunit of DNA, created in a laboratory and does not occur in nature. DNA sequences have been described which use newly created nucleobases to form a third base pair, in addition to the two ba
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are proteins, but in non-protein coding genes such as transfer RNA or small nuclear RNA genes, the product is a functional RNA; the process of gene expression is used by all known life—eukaryotes and utilized by viruses—to generate the macromolecular machinery for life. Several steps in the gene expression process may be modulated, including the transcription, RNA splicing and post-translational modification of a protein. Gene regulation gives the cell control over structure and function, is the basis for cellular differentiation and the versatility and adaptability of any organism. Gene regulation may serve as a substrate for evolutionary change, since control of the timing and amount of gene expression can have a profound effect on the functions of the gene in a cell or in a multicellular organism. In genetics, gene expression is the most fundamental level at which the genotype gives rise to the phenotype, i.e. observable trait.
The genetic code stored in DNA is "interpreted" by gene expression, the properties of the expression give rise to the organism's phenotype. Such phenotypes are expressed by the synthesis of proteins that control the organism's shape, or that act as enzymes catalysing specific metabolic pathways characterising the organism. Regulation of gene expression is thus critical to an organism's development. A gene is a stretch of DNA. Genomic DNA consists of two antiparallel and reverse complementary strands, each having 5' and 3' ends. With respect to a gene, the two strands may be labeled the "template strand," which serves as a blueprint for the production of an RNA transcript, the "coding strand," which includes the DNA version of the transcript sequence.. The production of the RNA copy of the DNA is called transcription, is performed in the nucleus by RNA polymerase, which adds one RNA nucleotide at a time to a growing RNA strand as per the complementarity law of the bases; this RNA is complementary to the template 3' → 5' DNA strand, itself complementary to the coding 5' → 3' DNA strand.
Therefore, the resulting 5' → 3' RNA strand is identical to the coding DNA strand with the exception that Thymines are replaced with uracils in the RNA. A coding DNA strand reading "ATG" is indirectly transcribed through the “TAC” in the non-coding template strand as "AUG" in the mRNA. In prokaryotes, transcription is carried out by a single type of RNA polymerase, which needs a DNA sequence called a Pribnow box as well as a sigma factor to start transcription. In eukaryotes, transcription is performed by three types of RNA polymerases, each of which needs a special DNA sequence called the promoter and a set of DNA-binding proteins—transcription factors—to initiate the process. RNA polymerase. RNA polymerase II transcribes all protein-coding genes but some non-coding RNAs. Pol II includes a C-terminal domain, rich in serine residues; when these residues are phosphorylated, the CTD binds to various protein factors that promote transcript maturation and modification. RNA polymerase III transcribes 5S rRNA, transfer RNA genes, some small non-coding RNAs.
Transcription ends. While transcription of prokaryotic protein-coding genes creates messenger RNA, ready for translation into protein, transcription of eukaryotic genes leaves a primary transcript of RNA, which first has to undergo a series of modifications to become a mature mRNA; these include 5' capping, set of enzymatic reactions that add 7-methylguanosine to the 5' end of pre-mRNA and thus protect the RNA from degradation by exonucleases. The m7G cap is bound by cap binding complex heterodimer, which aids in mRNA export to cytoplasm and protect the RNA from decapping. Another modification is 3' polyadenylation, they occur if polyadenylation signal sequence is present in pre-mRNA, between protein-coding sequence and terminator. The pre-mRNA is first cleaved and a series of ~200 adenines are added to form poly tail, which protects the RNA from degradation. Poly tail is bound by multiple poly-binding proteins necessary for mRNA export and translation re-initiation. A important modification of eukaryotic pre-mRNA is RNA splicing.
The majority of eukaryotic pre-mRNAs consist of alternating segments called introns. During the process of splicing, an RNA-protein catalytical complex known as spliceosome catalyzes two transesterification reactions, which remove an intron and release it in form of lariat structure, splice neighbouring exons together. In certain cases, some introns or exons can be either removed or retained in mature mRNA; this so-called alternative splicing creates series of different transcripts originating from a single gene. Because these transcripts can be translated into different proteins, splicing extends the complexity of eukaryotic gene expression. Extensive RNA processing may be an evolutionary advantage made possible by the nucleus of eukaryotes. In prokaryotes and translation happen together, whilst in eukaryotes, the nuclear membrane separates the two processes, giving time for RNA processing to
Asparagine, is an α-amino acid, used in the biosynthesis of proteins. It contains an α-amino group, an α-carboxylic acid group, a side chain carboxamide, classifying it as a polar, aliphatic amino acid, it is non-essential in humans. It is encoded by the codons AAU and AAC. A reaction between asparagine and reducing sugars or other source of carbonyls produces acrylamide in food when heated to sufficient temperature; these products occur in baked goods such as French fries, potato chips, toasted bread. Asparagine was first isolated in 1806 in a crystalline form by French chemists Louis Nicolas Vauquelin and Pierre Jean Robiquet from asparagus juice, in which it is abundant, hence the chosen name, it was the first amino acid to be isolated. Three years in 1809, Pierre Jean Robiquet identified a substance from liquorice root with properties which he qualified as similar to those of asparagine, which Plisson identified in 1828 as asparagine itself; the determination of asparagine's structure required decades of research.
The empirical formula for asparagine was first determined in 1833 by the French chemists Antoine François Boutron Charlard and Théophile-Jules Pelouze. In 1846 the Italian chemist Raffaele Piria treated asparagine with nitrous acid, which removed the molecule's amine groups and transformed asparagine into malic acid; this revealed the molecule's fundamental structure: a chain of four carbon atoms. Piria thought. In 1886, the Italian chemist Arnaldo Piutti discovered a mirror image or "enantiomer" of the natural form of asparagine, which shared many of asparagine's properties, but which differed from it. Since the structure of asparagine was still not known – the location of the amine group within the molecule was still not settled – Piutti synthesized asparagine and thus determined its true structure. Since the asparagine side-chain can form hydrogen bond interactions with the peptide backbone, asparagine residues are found near the beginning of alpha-helices as asx turns and asx motifs, in similar turn motifs, or as amide rings, in beta sheets.
Its role can be thought as "capping" the hydrogen bond interactions that would otherwise be satisfied by the polypeptide backbone. Asparagine provides key sites for N-linked glycosylation, modification of the protein chain with the addition of carbohydrate chains. A carbohydrate tree can be added to an asparagine residue if the latter is flanked on the C side by X-serine or X-threonine, where X is any amino acid with the exception of proline. Asparagine can be hydroxylated in the HIF1 hypoxia inducible transcription factor; this modification inhibits HIF1-mediated gene activation. Asparagine is not essential for humans, which means that it can be synthesized from central metabolic pathway intermediates and is not required in the diet. Asparagine is found in: Animal sources: dairy, beef, eggs, lactalbumin, seafood Plant sources: asparagus, legumes, seeds, whole grains The precursor to asparagine is oxaloacetate. Oxaloacetate is converted to aspartate using a transaminase enzyme; the enzyme transfers the amino group from glutamate to oxaloacetate producing α-ketoglutarate and aspartate.
The enzyme asparagine synthetase produces asparagine, AMP, pyrophosphate from aspartate, ATP. In the asparagine synthetase reaction, ATP is used to activate aspartate, forming β-aspartyl-AMP. Glutamine donates an ammonium group, which reacts with β-aspartyl-AMP to form asparagine and free AMP. Asparagine enters the citric acid cycle in humans as oxaloacetate. In bacteria, the degradation of asparagine leads to the production of oxaloacetate, the molecule which combines with citrate in the citric acid cycle. Asparagine is hydrolyzed to aspartate by asparaginase. Aspartate undergoes transamination to form glutamate and oxaloacetate from alpha-ketoglutarate. Asparagine is required for function of the brain, it plays an important role in the synthesis of ammonia. The addition of N-acetylglucosamine to asparagine is performed by oligosaccharyltransferase enzymes in the endoplasmic reticulum; this glycosylation is important both for protein function. According to a 2018 article in The Guardian, a study found that decreasing levels of asparagine "dramatically" reduced the spread of breast cancer in laboratory mice.
The article noted. GMD MS Spectrum Why Asparagus Makes Your Pee Stink
Vitamin B12 known as cobalamin, is a water-soluble vitamin, involved in the metabolism of every cell of the human body: it is a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It is important in the normal functioning of the nervous system via its role in the synthesis of myelin, in the maturation of developing red blood cells in the bone marrow. Vitamin B12 is one of eight B vitamins, it consists of a class of chemically related compounds. It contains the biochemically rare element cobalt positioned in the center of a corrin ring; the only organisms to produce vitamin B12 are certain bacteria, archaea. Some of these bacteria are found in the soil around the grasses; because there are no common vegetable sources of the vitamin, vegans must use a supplement or fortified foods for B12 intake or risk serious health consequences. Otherwise, most omnivorous people in developed countries obtain enough vitamin B12 from consuming animal products including meat, milk and fish. Staple foods those that form part of a vegan diet, are fortified by having the vitamin added to them.
Vitamin B12 supplements are available in single multivitamin tablets. The most common cause of vitamin B12 deficiency in developed countries is impaired absorption due to a loss of gastric intrinsic factor, which must be bound to food-source B12 in order for absorption to occur. Another group affected are those on long term antacid therapy, using proton pump inhibitors, H2 blockers or other antacids; this condition may be characterised by limb neuropathy or a blood disorder called pernicious anemia, a type of megaloblastic anemia. Folate levels in the individual may affect the course of pathological changes and symptomatology. Deficiency is more after age 60, increases in incidence with advancing age. Dietary deficiency is rare in developed countries due to access to dietary meat and fortified foods, but children in some regions of developing countries are at particular risk due to increased requirements during growth coupled with lack of access to dietary B12. Other causes of vitamin B12 deficiency are much less frequent.
B12 is the most chemically complex of all the vitamins. The structure of B12 is based on a corrin ring, similar to the porphyrin ring found in heme; the central metal ion is cobalt. Four of the six coordination sites are provided by the corrin ring, a fifth by a dimethylbenzimidazole group; the sixth coordination site, the reactive center, is variable, being a cyano group, a hydroxyl group, a methyl group or a 5′-deoxyadenosyl group (here the C5′ atom of the deoxyribose forms the covalent bond with cobalt to yield the four vitamers of B12. The covalent C-Co bond is one of the first examples of carbon-metal bonds to be discovered in biology; the hydrogenases and, by necessity, enzymes associated with cobalt utilization, involve metal-carbon bonds. Vitamin B12 is a generic descriptor name referring to a collection of cobalt and corrin ring molecules which are defined by their particular vitamin function in the body. All of the substrate cobalt-corrin molecules from which B12 is made must be synthesized by bacteria.
After this synthesis is complete, the human body has the ability to convert any form of B12 to an active form, by means of enzymatically removing certain prosthetic chemical groups from the cobalt atom and replacing them with others. The four vitamers of B12 are all red-colored crystals and water solutions, due to the color of the cobalt-corrin complex. Cyanocobalamin is one form of B12 because it can be metabolized in the body to an active coenzyme form; the cyanocobalamin form of B12 does not occur in nature but is a byproduct of the fact that other forms of B12 are avid binders of cyanide which they pick up in the process of activated charcoal purification of the vitamin after it is made by bacteria in the commercial process. Since the cyanocobalamin form of B12 is easy to crystallize and is not sensitive to air-oxidation, it is used as a form of B12 for food additives and in many common multivitamins. Pure cyanocobalamin possesses the deep pink color associated with most octahedral cobalt complexes and the crystals are well formed and grown up to millimeter size.
Hydroxocobalamin is another vitamer of B12 encountered in pharmacology, but is not present in the human body. Hydroxocobalamin is sometimes denoted B12a; this is the form of B12 produced by bacteria, and, converted to cyanocobalmin in the commercial charcoal filtration step of production. Hydroxocobalamin has an avid affinity for cyanide ions and has been used as an antidote to cyanide poisoning, it is supplied in water solution for injection. Hydroxocobalamin is thought to be converted to the active enzymic forms of B12 more than cyanocobalamin, since it is little more expensive than cyanocobalamin, has longer retention times in the body, has been used for vitamin replacement in situations where added reassurance of activity is desired. Intramuscular administration of hydroxocobalamin is the preferred treatment for pediatric patients with intrinsic cobalamin metabolic diseases, for vitamin B12 deficient patients with tobacco amblyopia.
Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosomes, which are the non-sex chromosomes. Chromosome 1 spans about 249 million nucleotide base pairs, which are the basic units of information for DNA, it represents about 8% of the total DNA in human cells. It was the last completed chromosome, sequenced two decades after the beginning of the Human Genome Project; the following are some of the gene count estimates of human chromosome 1. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies. Among various projects, the collaborative consensus coding sequence project takes an conservative strategy. So CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes; the following is a partial list of genes on human chromosome 1. For complete list, see the link in the infobox on the right. DENN1B hypothesized to be related to asthma Partial list of the genes located on p-arm of human chromosome 1: Partial list of the genes located on q-arm of human chromosome 1: There are 890 known diseases related to this chromosome.
Some of these diseases are hearing loss, Alzheimer's disease and breast cancer. Rearrangements and mutations of chromosome 1 are prevalent in cancer and many other diseases. Patterns of sequence variation reveal signals of recent selection in specific genes that may contribute to human fitness, in regions where no function is evident. Complete monosomy is invariably lethal before birth. Complete trisomy is lethal within days after conception; some partial deletions and partial duplications produce birth defects. The following diseases are some of those related to genes on chromosome 1: National Institutes of Health. "Chromosome 1". Genetics Home Reference. Retrieved 2017-05-06. "Final genome'chapter' published". BBC NEWS. 2006-05-18. Retrieved 2017-05-06. "Chromosome 1". Human Genome Project Information Archive 1990–2003. Retrieved 2017-05-06
In biology, a gene is a sequence of nucleotides in DNA or RNA that codes for a molecule that has a function. During gene expression, the DNA is first copied into RNA; the RNA can be directly functional or be the intermediate template for a protein that performs a function. The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic trait; these genes make up different DNA sequences called genotypes. Genotypes along with developmental factors determine what the phenotypes will be. Most biological traits are under the influence of polygenes as well as gene–environment interactions; some genetic traits are visible, such as eye color or number of limbs, some are not, such as blood type, risk for specific diseases, or the thousands of basic biochemical processes that constitute life. Genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population; these alleles encode different versions of a protein, which cause different phenotypical traits.
Usage of the term "having a gene" refers to containing a different allele of the same, shared gene. Genes evolve due to natural selection / survival of the fittest and genetic drift of the alleles; the concept of a gene continues to be refined. For example, regulatory regions of a gene can be far removed from its coding regions, coding regions can be split into several exons; some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. Therefore, a broad, modern working definition of a gene is any discrete locus of heritable, genomic sequence which affect an organism's traits by being expressed as a functional product or by regulation of gene expression; the term gene was introduced by Danish botanist, plant physiologist and geneticist Wilhelm Johannsen in 1909. It is inspired by the ancient Greek: γόνος, that means offspring and procreation; the existence of discrete inheritable units was first suggested by Gregor Mendel. From 1857 to 1864, in Brno, he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring.
He described these mathematically as 2n combinations where n is the number of differing characteristics in the original peas. Although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics; this description prefigured Wilhelm Johannsen's distinction between phenotype. Mendel was the first to demonstrate independent assortment, the distinction between dominant and recessive traits, the distinction between a heterozygote and homozygote, the phenomenon of discontinuous inheritance. Prior to Mendel's work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilisation process and that the traits of the parents blended and mixed to produce the offspring. Charles Darwin developed a theory of inheritance he termed pangenesis, from Greek pan and genesis / genos. Darwin used the term gemmule to describe hypothetical particles. Mendel's work went unnoticed after its first publication in 1866, but was rediscovered in the late 19th century by Hugo de Vries, Carl Correns, Erich von Tschermak, who reached similar conclusions in their own research.
In 1889, Hugo de Vries published his book Intracellular Pangenesis, in which he postulated that different characters have individual hereditary carriers and that inheritance of specific traits in organisms comes in particles. De Vries called these units "pangenes", after Darwin's 1868 pangenesis theory. Sixteen years in 1905, Wilhelm Johannsen introduced the term'gene' and William Bateson that of'genetics' while Eduard Strasburger, amongst others, still used the term'pangene' for the fundamental physical and functional unit of heredity. Advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid was shown to be the molecular repository of genetic information by experiments in the 1940s to 1950s; the structure of DNA was studied by Rosalind Franklin and Maurice Wilkins using X-ray crystallography, which led James D. Watson and Francis Crick to publish a model of the double-stranded DNA molecule whose paired nucleotide bases indicated a compelling hypothesis for the mechanism of genetic replication.
In the early 1950s the prevailing view was that the genes in a chromosome acted like discrete entities, indivisible by recombination and arranged like beads on a string. The experiments of Benzer using mutants defective in the rII region of bacteriophage T4 showed that individual genes have a simple linear structure and are to be equivalent to a linear section of DNA. Collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, transcribed from DNA; this dogma has since been shown to have exceptions, such as reverse transcription in retroviruses. The modern study of genetics at the level of DNA is known as molecular genetics. In 1972, Walter Fiers and his team were the first to determine the sequence of a gene: that of Bacteriophage MS2 coat protein; the subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing and turned it into a routine laboratory tool.
An automated version of the Sanger method was used in early phases of the
Zinc is a chemical element with symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state, the Zn2+ and Mg2+ ions are of similar size. Zinc has five stable isotopes; the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia and the United States. Zinc is refined by froth flotation of the ore and final extraction using electricity. Brass, an alloy of copper and zinc in various proportions, was used as early as the third millennium BC in the Aegean, the United Arab Emirates, Kalmykia and Georgia, the second millennium BC in West India, Iran, Syria and Israel/Palestine. Zinc metal was not produced on a large scale until the 12th century in India, though it was known to the ancient Romans and Greeks; the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, as early as the 9th century AD when a distillation process was employed to make pure zinc.
Alchemists burned zinc in air to form what they called "philosopher's wool" or "white snow". The element was named by the alchemist Paracelsus after the German word Zinke. German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746. Work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the major application for zinc. Other applications are in electrical batteries, small non-structural castings, alloys such as brass. A variety of zinc compounds are used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide, dimethylzinc or diethylzinc in the organic laboratory. Zinc is an essential mineral, including to postnatal development. Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, diarrhea.
Enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc may cause ataxia and copper deficiency. Zinc is a bluish-white, diamagnetic metal, though most common commercial grades of the metal have a dull finish, it is somewhat less dense than iron and has a hexagonal crystal structure, with a distorted form of hexagonal close packing, in which each atom has six nearest neighbors in its own plane and six others at a greater distance of 290.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has low melting and boiling points; the melting point is the lowest of all the d-block metals aside from cadmium. Many alloys contain zinc, including brass. Other metals long known to form binary alloys with zinc are aluminium, bismuth, iron, mercury, tin, cobalt, nickel and sodium.
Although neither zinc nor zirconium are ferromagnetic, their alloy ZrZn2 exhibits ferromagnetism below 35 K. A bar of zinc generates a characteristic sound when bent, similar to tin cry. Zinc makes up about 75 ppm of Earth's crust. Soil contains zinc in 5–770 ppm with an average 64 ppm. Seawater has only 30 ppb and the atmosphere, 0.1–4 µg/m3. The element is found in association with other base metals such as copper and lead in ores. Zinc is a chalcophile, meaning the element is more to be found in minerals together with sulfur and other heavy chalcogens, rather than with the light chalcogen oxygen or with non-chalcogen electronegative elements such as the halogens. Sulfides formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, a form of zinc sulfide, is the most mined zinc-containing ore because its concentrate contains 60–62% zinc. Other source minerals for zinc include smithsonite, hemimorphite and sometimes hydrozincite. With the exception of wurtzite, all these other minerals were formed by weathering of the primordial zinc sulfides.
Identified world zinc resources total about 1.9–2.8 billion tonnes. Large deposits are in Australia and the United States, with the largest reserves in Iran; the most recent estimate of reserve base for zinc was made in 2009 and calculated to be 480 Mt. Zinc reserves, on the other hand, are geologically identified ore bodies whose suitability for recovery is economically based at the time of determination. Since exploration and mine development is an ongoing process, the amount of zinc reserves is not a fixed number and sustainability of zinc ore supplies cannot be judged by extrapolating the combined mine life of today's zinc mines; this concept is well supported by data from the United States Geol