Amino acids are organic compounds containing amine and carboxyl functional groups, along with a side chain specific to each amino acid. The key elements of an amino acid are carbon, hydrogen and nitrogen, although other elements are found in the side chains of certain amino acids. About 500 occurring amino acids are known and can be classified in many ways, they can be classified according to the core structural functional groups' locations as alpha-, beta-, gamma- or delta- amino acids. In the form of proteins, amino acid residues form the second-largest component of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis. In biochemistry, amino acids having both the amine and the carboxylic acid groups attached to the first carbon atom have particular importance, they are known as α-amino acids. They include the 22 proteinogenic amino acids, which combine into peptide chains to form the building-blocks of a vast array of proteins.
These are all L-stereoisomers, although a few D-amino acids occur in bacterial envelopes, as a neuromodulator, in some antibiotics. Twenty of the proteinogenic amino acids are encoded directly by triplet codons in the genetic code and are known as "standard" amino acids; the other two are selenocysteine, pyrrolysine. Pyrrolysine and selenocysteine are encoded via variant codons. N-formylmethionine is considered as a form of methionine rather than as a separate proteinogenic amino acid. Codon–tRNA combinations not found in nature can be used to "expand" the genetic code and form novel proteins known as alloproteins incorporating non-proteinogenic amino acids. Many important proteinogenic and non-proteinogenic amino acids have biological functions. For example, in the human brain and gamma-amino-butyric acid are the main excitatory and inhibitory neurotransmitters. Hydroxyproline, a major component of the connective tissue collagen, is synthesised from proline. Glycine is a biosynthetic precursor to porphyrins used in red blood cells.
Carnitine is used in lipid transport. Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food. Others may be conditionally essential for medical conditions. Essential amino acids may differ between species; because of their biological significance, amino acids are important in nutrition and are used in nutritional supplements, fertilizers and food technology. Industrial uses include the production of drugs, biodegradable plastics, chiral catalysts; the first few amino acids were discovered in the early 19th century. In 1806, French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet isolated a compound in asparagus, subsequently named asparagine, the first amino acid to be discovered. Cystine was discovered in 1810, although its monomer, remained undiscovered until 1884. Glycine and leucine were discovered in 1820; the last of the 20 common amino acids to be discovered was threonine in 1935 by William Cumming Rose, who determined the essential amino acids and established the minimum daily requirements of all amino acids for optimal growth.
The unity of the chemical category was recognized by Wurtz in 1865, but he gave no particular name to it. Usage of the term "amino acid" in the English language is from 1898, while the German term, Aminosäure, was used earlier. Proteins were found to yield amino acids after enzymatic acid hydrolysis. In 1902, Emil Fischer and Franz Hofmeister independently proposed that proteins are formed from many amino acids, whereby bonds are formed between the amino group of one amino acid with the carboxyl group of another, resulting in a linear structure that Fischer termed "peptide". In the structure shown at the top of the page, R represents a side chain specific to each amino acid; the carbon atom next to the carboxyl group is called the α–carbon. Amino acids containing an amino group bonded directly to the alpha carbon are referred to as alpha amino acids; these include amino acids such as proline which contain secondary amines, which used to be referred to as "imino acids". The alpha amino acids are the most common form found in nature, but only when occurring in the L-isomer.
The alpha carbon is a chiral carbon atom, with the exception of glycine which has two indistinguishable hydrogen atoms on the alpha carbon. Therefore, all alpha amino acids but glycine can exist in either of two enantiomers, called L or D amino acids, which are mirror images of each other. While L-amino acids represent all of the amino acids found in proteins during translation in the ribosome, D-amin
The Parvoviridae are a family of small, genetically-compact DNA viruses, known collectively as parvoviruses. There are >75 species in the family, divided among 13 genera and two subfamilies. Members of this family infect a wide array of animal hosts and have been divided into two subfamilies, which infect either vertebrates or invertebrates. Parvovirus B19 was the first pathogenic human parvovirus to be discovered and is best known for causing a childhood exanthem called "fifth disease", although it is associated with other diseases including arthritis. Canine parvovirus causes a contagious disease in dogs. In cats, a parvovirus causes feline distemper. Parvovirus particles have a durable non-enveloped protein capsid ~20–30 nm in diameter that contains a single copy of the linear single-stranded ~ 5kb DNA genome, which terminates in small imperfect palindromes that fold into dynamic hairpin telomeres; these terminal hairpins are hallmarks of the family, giving rise to the viral origins of DNA replication and mediating multiple steps in the viral life cycle including genome amplification and the establishment of transcription complexes.
However, they are refractory to detection by PCR amplification strategies since they tend to induce polymerase strand-switching. Many parvoviruses are exceptionally resistant to inactivation, remaining infectious for months or years after release into the environment. Viruses in this family have small protein virions, their capsid shells are assembled from 60 icosahedrally-ordered copies of a single core protein sequence, but some of these VP proteins have N-terminal extensions that are not visible in X-ray structures. Biochemical and serological studies indicate that these extensions become successively exposed at the particle surface during virus maturation and cell entry, where they contribute to virion stability and mediate specific steps in cell trafficking. Parvoviruses appear to be unique in encoding a broad spectrum phospholipase A2 activity in the N-terminus of the longest subset of their capsid proteins, deployed to mediate virion transfer across the lipid bilayer of host cells The viral genome is 4–6 kilobases in length and terminates in imperfectly-palindromic hairpin sequences of ~120–500 nucleotides that exhibit genus-specific secondary structures, can either be identical at the two ends of the genome or can differ in size and predicted secondary structure.
Homotelomeric viruses package DNA strands of both senses whereas heterotelomeric viruses package predominantly negative-sense DNA. All parvoviruses encode two major gene complexes: the non-structural gene that encodes the replication initiator protein, the VP gene, which encodes a nested set of ~2–6 size variants derived from the C-terminus of the single VP protein sequence. Members of the Parvovirinae encode a few small genus-specific ancillary proteins that are variably distributed throughout the genome, show little sequence homology to each other, appear to serve an array of different functions in each genus. Viruses in most genera are mono-sense, meaning that both viral genes are transcribed in a single direction from open reading frames in the same DNA strand, but members of one genus of homotelomeric invertebrate viruses show ambisense organization, with the NS and capsid proteins being transcribed in opposite directions from the 5’-ends of the two complementary DNA strands; the major non-structural protein, NS1, is a site- and strand-specific endonuclease belonging to the HuH protein superfamily, carries a AAA+ SF3 helicase domain.
NS1 initiates and drives the viral “rolling hairpin” replication mechanism, a linear adaptation of the more-common “rolling-circle” replication strategy used by many small circular prokaryotic and viral replicons. RHR is a unidirectional mechanism that displaces a single, continuous DNA strand, which folds and refolds to generate a series of concatemeric duplex replication intermediates. Unit length genomes are excised from these intermediates by the NS1 endonuclease, packaged 3’-to-5’ into preformed empty capsids driven by the SF3 helicase activity of NS1/Rep. Viral replication is nuclear. Entry into the host cell is achieved by attachment to host receptors, which mediate internalization via endocytosis. Capsids are metastable, undergoing a series of structural shifts during cell entry that sequentially expose peptides carrying PLA2 activity and trafficking signals; these signals mediate delivery of the intact virion into the cell nucleus, where genome uncoating allows the establishment of viral DNA replication and transcription complexes that rely predominantly upon the synthetic machinery of their host cell.
Replication follows the unidirectional strand displacement mechanism discussed above. Packaged virions from viruses in at least two genera have mechanisms that allow mature virions to be trafficked out of viable host cells prior to cell lysis, but members of most other genera are only released into the environment following death and lysis of the infected cell. Natural animal hosts for parvoviruses include a wide range of vertebrates and echinoderms. For viruses in the Parvovirinae transmission routes are fecal-oral or respiratory. A virion attaches to receptors on the surface of a potential host cell. In the case of B19
A DNA virus is a virus that has DNA as its genetic material and replicates using a DNA-dependent DNA polymerase. The nucleic acid is double-stranded DNA but may be single-stranded DNA. DNA viruses belong to either Group Group II of the Baltimore classification system for viruses. Single-stranded DNA is expanded to double-stranded in infected cells. Although Group VII viruses such as hepatitis B contain a DNA genome, they are not considered DNA viruses according to the Baltimore classification, but rather reverse transcribing viruses because they replicate through an RNA intermediate. Notable diseases like smallpox and the chickenpox are caused by such DNA viruses. Genome organization within this group varies considerably; some have circular genomes. Some families have circularly permuted linear genomes. Others have linear genomes with covalently closed ends. A virus infecting archaea was first described in 1974. Several others have been described since: most have head-tail morphologies and linear double-stranded DNA genomes.
Other morphologies have been described: spindle shaped, rod shaped, filamentous and spherical. Additional morphological types may exist. Orders within this group are defined on the basis of morphology rather than DNA sequence similarity, it is thought that morphology is more conserved in this group than sequence similarity or gene order, variable. Three orders and 31 families are recognised. A fourth order — Megavirales — for the nucleocytoplasmic large DNA viruses has been proposed; this proposal has yet to be ratified by the ICTV. Four genera are recognised. Fifteen families are enveloped; these include all three families in the order Herpesvirales and the following families: Ascoviridae, Asfarviridae, Fuselloviridae, Guttaviridae, Iridoviridae, Lipothrixviridae and Poxviridae. Bacteriophages belonging to the families Tectiviridae and Corticoviridae have a lipid bilayer membrane inside the icosahedral protein capsid and the membrane surrounds the genome; the crenarchaeal virus Sulfolobus turreted.
The genomes in this group vary from ~10 kilobases to over 2.5 megabases in length. The largest bacteriophage known is Klebsiella Phage vB_KleM-RaK2 which has a genome of 346 kilobases; the virophages are a group of viruses. A virus with a novel method of genome packing infecting species of the genus Sulfolobus has been described; as this virus does not resemble any known virus it has been classified into a new family, the Portogloboviridae. Another Sulfolobus infecting virus - Sulfolobus ellipsoid virus 1 - has been described; this enveloped virus may be classified into a new taxon. Species of the order Caudovirales and of the families Corticoviridae and Tectiviridae infect bacteria. Species of the order Ligamenvirales and the families Ampullaviridae, Clavaviridae, Globuloviridae, Guttaviridae and Turriviridae infect hyperthermophilic archaea species of the Crenarchaeota. Species of the order Herpesvirales and of the families Adenoviridae, Iridoviridae, Papillomaviridae and Poxviridae infect vertebrates.
Species of the families Ascovirus, Hytrosaviridae and Polydnaviruses and of the genus Nudivirus infect insects. Species of the family Mimiviridae and the species Marseillevirus, Mavirus virophage and Sputnik virophage infect protozoa. Species of the family Nimaviridae infect crustaceans. Species of the family Phycodnaviridae and the species Organic Lake virophage infect algae; these are the only known dsDNA viruses. Species of the family Plasmaviridae infect species of the class Mollicutes. Species of the family Pandoraviridae infect amoebae. Species of the genus Dinodnavirus infect dinoflagellates; these are the only known viruses. Species of the genus Rhizidiovirus infect stramenopiles; these are the only known dsDNA viruses. Species of the genus Salterprovirus and Sphaerolipoviridae infect species of the Euryarchaeota. Order Caudovirales Family Myoviridae—includes Enterobacteria phage T4 Family Podoviridae—includes Enterobacteria phage T7 Family Siphoviridae—includes Enterobacteria phage λ Order Herpesvirales Family Alloherpesviridae Family Herpesviridae—includes human herpesviruses, Varicella Zoster virus Family Malacoherpesviridae Order Ligamenvirales Family Lipothrixviridae Family Rudiviridae Unassigned families Family Adenoviridae—includes viruses which cause human adenovirus infection Family Ampullaviridae Family Ascoviridae Family Asfarviridae—includes African swine fever virus Family Baculoviridae Family Bicaudaviridae Family Clavaviridae Family Corticoviridae Family Fuselloviridae Family Globuloviridae Family Guttaviridae Family Hytrosaviridae Family Iridoviridae Family Lavidaviridae Family Marseilleviridae Family Mimiviridae Family Nudiviridae Family Nimaviridae Family Pandoraviridae Family Papillomaviridae Family Phycodnaviridae Family Plasmaviridae Family Polydnaviruses Family Polyomaviridae—includes Simian virus 40, JC virus, BK virus Family Poxviridae—includes Cowpox virus, smallpox Family Sphaerolipoviridae Family Tectiviridae Family Tristromaviridae Family Turriviridae Unassigned genera Dinodnavirus Salterprovirus Rhizidiovirus Unassigned species Abalone shriveling syndrome-associated virus Bandicoot papillomatosis carcinomatosis vi
In the fields of molecular biology and genetics, a genome is the genetic material of an organism. It consists of DNA; the genome includes both the genes and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA. The study of the genome is called genomics; the term genome was created in 1920 by Hans Winkler, professor of botany at the University of Hamburg, Germany. The Oxford Dictionary suggests the name is a blend of the words chromosome. However, see omics for a more thorough discussion. A few related -ome words existed, such as biome and rhizome, forming a vocabulary into which genome fits systematically. A genome sequence is the complete list of the nucleotides that make up all the chromosomes of an individual or a species. Within a species, the vast majority of nucleotides are identical between individuals, but sequencing multiple individuals is necessary to understand the genetic diversity. In 1976, Walter Fiers at the University of Ghent was the first to establish the complete nucleotide sequence of a viral RNA-genome.
The next year, Fred Sanger completed the first DNA-genome sequence: Phage Φ-X174, of 5386 base pairs. The first complete genome sequences among all three domains of life were released within a short period during the mid-1990s: The first bacterial genome to be sequenced was that of Haemophilus influenzae, completed by a team at The Institute for Genomic Research in 1995. A few months the first eukaryotic genome was completed, with sequences of the 16 chromosomes of budding yeast Saccharomyces cerevisiae published as the result of a European-led effort begun in the mid-1980s; the first genome sequence for an archaeon, Methanococcus jannaschii, was completed in 1996, again by The Institute for Genomic Research. The development of new technologies has made genome sequencing cheaper and easier, the number of complete genome sequences is growing rapidly; the US National Institutes of Health maintains one of several comprehensive databases of genomic information. Among the thousands of completed genome sequencing projects include those for rice, a mouse, the plant Arabidopsis thaliana, the puffer fish, the bacteria E. coli.
In December 2013, scientists first sequenced the entire genome of a Neanderthal, an extinct species of humans. The genome was extracted from the toe bone of a 130,000-year-old Neanderthal found in a Siberian cave. New sequencing technologies, such as massive parallel sequencing have opened up the prospect of personal genome sequencing as a diagnostic tool, as pioneered by Manteia Predictive Medicine. A major step toward that goal was the completion in 2007 of the full genome of James D. Watson, one of the co-discoverers of the structure of DNA. Whereas a genome sequence lists the order of every DNA base in a genome, a genome map identifies the landmarks. A genome map is less detailed than aids in navigating around the genome; the Human Genome Project was organized to sequence the human genome. A fundamental step in the project was the release of a detailed genomic map by Jean Weissenbach and his team at the Genoscope in Paris. Reference genome sequences and maps continue to be updated, removing errors and clarifying regions of high allelic complexity.
The decreasing cost of genomic mapping has permitted genealogical sites to offer it as a service, to the extent that one may submit one's genome to crowdsourced scientific endeavours such as DNA. LAND at the New York Genome Center, an example both of the economies of scale and of citizen science. Viral genomes can be composed of either RNA or DNA; the genomes of RNA viruses can be either single-stranded or double-stranded RNA, may contain one or more separate RNA molecules. DNA viruses can have either double-stranded genomes. Most DNA virus genomes are composed of a single, linear molecule of DNA, but some are made up of a circular DNA molecule. Prokaryotes and eukaryotes have DNA genomes. Archaea have a single circular chromosome. Most bacteria have a single circular chromosome. If the DNA is replicated faster than the bacterial cells divide, multiple copies of the chromosome can be present in a single cell, if the cells divide faster than the DNA can be replicated, multiple replication of the chromosome is initiated before the division occurs, allowing daughter cells to inherit complete genomes and partially replicated chromosomes.
Most prokaryotes have little repetitive DNA in their genomes. However, some symbiotic bacteria have reduced genomes and a high fraction of pseudogenes: only ~40% of their DNA encodes proteins; some bacteria have auxiliary genetic material part of their genome, carried in plasmids. For this, the word genome should not be used as a synonym of chromosome. Eukaryotic genomes are composed of one or more linear DNA chromosomes; the number of chromosomes varies from Jack jumper ants and an asexual nemotode, which each have only one pair, to a fern species that has 720 pairs. A typical human cell has two copies of each of 22 autosomes, one inherited from each parent, plus two sex chromosomes, making it diploid. Gametes, such as ova, sperm and pollen, are haploid, meaning they carry only one copy of each chromosome. In addition to the chromosomes in the nucleus, organelles such as the chloroplasts and mitochondria have their own DNA. Mitochondria are sometimes said to have their own genome referred to as the "mitochondrial genome".
The DNA found within the chloroplast may be referred to as the "plastome". Like the bacteria they originated from and chloroplasts have a circular chromosome
Africa is the world's second largest and second most-populous continent, being behind Asia in both categories. At about 30.3 million km2 including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area. With 1.2 billion people as of 2016, it accounts for about 16% of the world's human population. The continent is surrounded by the Mediterranean Sea to the north, the Isthmus of Suez and the Red Sea to the northeast, the Indian Ocean to the southeast and the Atlantic Ocean to the west; the continent includes various archipelagos. It contains 54 recognised sovereign states, nine territories and two de facto independent states with limited or no recognition; the majority of the continent and its countries are in the Northern Hemisphere, with a substantial portion and number of countries in the Southern Hemisphere. Africa's average population is the youngest amongst all the continents. Algeria is Africa's largest country by area, Nigeria is its largest by population. Africa central Eastern Africa, is accepted as the place of origin of humans and the Hominidae clade, as evidenced by the discovery of the earliest hominids and their ancestors as well as ones that have been dated to around 7 million years ago, including Sahelanthropus tchadensis, Australopithecus africanus, A. afarensis, Homo erectus, H. habilis and H. ergaster—the earliest Homo sapiens, found in Ethiopia, date to circa 200,000 years ago.
Africa encompasses numerous climate areas. Africa hosts a large diversity of ethnicities and languages. In the late 19th century, European countries colonised all of Africa. African nations cooperate through the establishment of the African Union, headquartered in Addis Ababa. Afri was a Latin name used to refer to the inhabitants of then-known northern Africa to the west of the Nile river, in its widest sense referred to all lands south of the Mediterranean; this name seems to have referred to a native Libyan tribe, an ancestor of modern Berbers. The name had been connected with the Phoenician word ʿafar meaning "dust", but a 1981 hypothesis has asserted that it stems from the Berber word ifri meaning "cave", in reference to cave dwellers; the same word may be found in the name of the Banu Ifran from Algeria and Tripolitania, a Berber tribe from Yafran in northwestern Libya. Under Roman rule, Carthage became the capital of the province it named Africa Proconsularis, following its defeat of the Carthaginians in the Third Punic War in 146 BC, which included the coastal part of modern Libya.
The Latin suffix -ica can sometimes be used to denote a land. The Muslim region of Ifriqiya, following its conquest of the Byzantine Empire's Exarchatus Africae preserved a form of the name. According to the Romans, Africa lay to the west of Egypt, while "Asia" was used to refer to Anatolia and lands to the east. A definite line was drawn between the two continents by the geographer Ptolemy, indicating Alexandria along the Prime Meridian and making the isthmus of Suez and the Red Sea the boundary between Asia and Africa; as Europeans came to understand the real extent of the continent, the idea of "Africa" expanded with their knowledge. Other etymological hypotheses have been postulated for the ancient name "Africa": The 1st-century Jewish historian Flavius Josephus asserted that it was named for Epher, grandson of Abraham according to Gen. 25:4, whose descendants, he claimed, had invaded Libya. Isidore of Seville in his 7th-century Etymologiae XIV.5.2. Suggests "Africa comes from the Latin aprica, meaning "sunny".
Massey, in 1881, stated that Africa is derived from the Egyptian af-rui-ka, meaning "to turn toward the opening of the Ka." The Ka is the energetic double of every person and the "opening of the Ka" refers to a womb or birthplace. Africa would be, for the Egyptians, "the birthplace." Michèle Fruyt in 1976 proposed linking the Latin word with africus "south wind", which would be of Umbrian origin and mean "rainy wind". Robert R. Stieglitz of Rutgers University in 1984 proposed: "The name Africa, derived from the Latin *Aphir-ic-a, is cognate to Hebrew Ophir." Ibn Khallikan and some other historians claim that the name of Africa came from a Himyarite king called Afrikin ibn Kais ibn Saifi called "Afrikus son of Abrahah" who subdued Ifriqiya. Africa is considered by most paleoanthropologists to be the oldest inhabited territory on Earth, with the human species originating from the continent. During the mid-20th century, anthropologists discovered many fossils and evidence of human occupation as early as 7 million years ago.
Fossil remains of several species of early apelike humans thought to have evolved into modern man, such as Australopithecus afarensis (radiometrically dated to 3.9–3.0 million years BP, Paranthropus boisei and Homo ergaster have been discovered. After the evolution of Homo sapiens sapiens 150,000 to 100,000 years BP in Africa, the continent was populated by groups of hunter-gatherers; these first modern humans left Africa and populated the rest of the globe during the Out of Africa II migration dated to 50,000 years BP, exiting the continent eith
A blood donation occurs when a person voluntarily has blood drawn and used for transfusions and/or made into biopharmaceutical medications by a process called fractionation. Donation may be of specific components directly. Blood banks participate in the collection process as well as the procedures that follow it. Today in the developed world, most blood donors are unpaid volunteers who donate blood for a community supply. In some countries, established supplies are limited and donors give blood when family or friends need a transfusion. Many donors donate as an act of charity, but in countries that allow paid donation some donors are paid, in some cases there are incentives other than money such as paid time off from work. Donors can have blood drawn for their own future use. Donating is safe, but some donors have bruising where the needle is inserted or may feel faint. Potential donors are evaluated for anything; the screening includes testing for diseases that can be transmitted by a blood transfusion, including HIV and viral hepatitis.
The donor must answer questions about medical history and take a short physical examination to make sure the donation is not hazardous to his or her health. How a donor can donate varies from days to months based on what component they donate and the laws of the country where the donation takes place. For example, in the United States, donors must wait eight weeks between whole blood donations but only seven days between plateletpheresis donations and twice per seven-day period in plasmapheresis; the amount of blood drawn and the methods vary. The collection can be done manually or with automated equipment that takes only specific components of the blood. Most of the components of blood used for transfusions have a short shelf life, maintaining a constant supply is a persistent problem; this has led to some increased interest in autotransfusion, whereby a patient's blood is salvaged during surgery for continuous reinfusion—or alternatively, is "self-donated" prior to when it will be needed. Blood donations are divided into groups based on.
An'allogeneic' donation is when a donor gives blood for storage at a blood bank for transfusion to an unknown recipient. A'directed' donation is when a person a family member, donates blood for transfusion to a specific individual. Directed donations are rare when an established supply exists. A'replacement donor' donation is a hybrid of the two and is common in developing countries such as Ghana. In this case, a friend or family member of the recipient donates blood to replace the stored blood used in a transfusion, ensuring a consistent supply; when a person has blood stored that will be transfused back to the donor at a date after surgery, called an'autologous' donation. Blood, used to make medications can be made from allogeneic donations or from donations used for manufacturing. Blood is sometimes collected using similar methods for therapeutic phlebotomy, similar to the ancient practice of bloodletting, used to treat conditions such as hereditary hemochromatosis or polycythemia vera; this blood is sometimes treated as a blood donation, but may be discarded if it cannot be used for transfusion or further manufacturing.
The actual process varies according to the laws of the country, recommendations to donors vary according to the collecting organization. The World Health Organization gives recommendations for blood donation policies, but in developing countries many of these are not followed. For example, the recommended testing requires laboratory facilities, trained staff, specialized reagents, all of which may not be available or too expensive in developing countries. An event where donors come to donate allogeneic blood is sometimes called a'blood drive' or a'blood donor session'; these can occur at a blood bank, but they are set up at a location in the community such as a shopping center, school, or house of worship. Donors are required to give consent for the process and this requirement means minors cannot donate without permission from a parent or guardian. In some countries, answers are associated with the donor's blood, but not name, to provide anonymity. If a potential donor does not meet these criteria, they are'deferred'.
This term is used. Blood banks in the United States may be required to label the blood if it is from a therapeutic donor, so some do not accept donations from donors with any blood disease. Others, such as the Australian Red Cross Blood Service, accept blood from donors with hemochromatosis, it is a genetic disorder. The donor's race or ethnic background is sometimes important since certain blood types rare ones, are more common in certain ethnic groups. In the United States donors were segregated or excluded on race, religion, or ethnicity, but this is no longer a standard practice. Donors are screened for health risks; some of these restrictions are controversial, such as restricting donations from men who have sex with men because of the risk of transmitting HIV. In 2011, the UK reduced its blanket
South America is a continent in the Western Hemisphere in the Southern Hemisphere, with a small portion in the Northern Hemisphere. It may be considered a subcontinent of the Americas, how it is viewed in the Spanish and Portuguese-speaking regions of the Americas; the reference to South America instead of other regions has increased in the last decades due to changing geopolitical dynamics. It is bordered on the west on the north and east by the Atlantic Ocean, it includes twelve sovereign states, a part of France, a non-sovereign area. In addition to this, the ABC islands of the Kingdom of the Netherlands and Tobago, Panama may be considered part of South America. South America has an area of 17,840,000 square kilometers, its population as of 2016 has been estimated at more than 420 million. South America ranks fourth in fifth in population. Brazil is by far the most populous South American country, with more than half of the continent's population, followed by Colombia, Argentina and Peru. In recent decades Brazil has concentrated half of the region's GDP and has become a first regional power.
Most of the population lives near the continent's western or eastern coasts while the interior and the far south are sparsely populated. The geography of western South America is dominated by the Andes mountains. Most of the continent lies in the tropics; the continent's cultural and ethnic outlook has its origin with the interaction of indigenous peoples with European conquerors and immigrants and, more locally, with African slaves. Given a long history of colonialism, the overwhelming majority of South Americans speak Portuguese or Spanish, societies and states reflect Western traditions. South America occupies the southern portion of the Americas; the continent is delimited on the northwest by the Darién watershed along the Colombia–Panama border, although some may consider the border instead to be the Panama Canal. Geopolitically and geographically all of Panama – including the segment east of the Panama Canal in the isthmus – is included in North America alone and among the countries of Central America.
All of mainland South America sits on the South American Plate. South America is home to Angel Falls in Venezuela. South America's major mineral resources are gold, copper, iron ore and petroleum; these resources found in South America have brought high income to its countries in times of war or of rapid economic growth by industrialized countries elsewhere. However, the concentration in producing one major export commodity has hindered the development of diversified economies; the fluctuation in the price of commodities in the international markets has led to major highs and lows in the economies of South American states causing extreme political instability. This is leading to efforts to diversify production to drive away from staying as economies dedicated to one major export. South America is one of the most biodiverse continents on earth. South America is home to many interesting and unique species of animals including the llama, piranha, vicuña, tapir; the Amazon rainforests possess high biodiversity, containing a major proportion of the Earth's species.
Brazil is the largest country in South America, encompassing around half of the continent's land area and population. The remaining countries and territories are divided among three regions: The Andean States, the Guianas and the Southern Cone. Traditionally, South America includes some of the nearby islands. Aruba, Curaçao, Trinidad and the federal dependencies of Venezuela sit on the northerly South American continental shelf and are considered part of the continent. Geo-politically, the island states and overseas territories of the Caribbean are grouped as a part or subregion of North America, since they are more distant on the Caribbean Plate though San Andres and Providencia are politically part of Colombia and Aves Island is controlled by Venezuela. Other islands that are included with South America are the Galápagos Islands that belong to Ecuador and Easter Island, Robinson Crusoe Island, Chiloé and Tierra del Fuego. In the Atlantic, Brazil owns Fernando de Noronha and Martim Vaz, the Saint Peter and Saint Paul Archipelago, while the Falkland Islands are governed by the United Kingdom, whose sovereignty over the islands is disputed by Argentina.
South Georgia and the South Sandwich Islands may be associate