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 bigger 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
Angus Stickler was the lead reporter for the Bureau of Investigative Journalism until his resignation in December 2012. In 2006 he was named News Journalist of the Year at the 24th Sony Radio Academy Awards. In 2011 he won the Thomson Reuters Europe award for the Bureau's investigation into EU structural funds. In 2011 he won an Amnesty International Media Award for his work on the Bureau's website. Stickler made the headlines in November 2012 when an investigation he led for the BBC programme Newsnight was found to have falsely implicated a former senior Conservative politician in the North Wales child abuse scandal; the person, the focus of the Newsnight broadcast, despite not being named, was identified on the internet as the former Conservative Party Treasurer Lord McAlpine. Lord McAlpine issued a statement denying the accusations; this allegation was subsequently admitted by the BBC to be false. The broadcasting of the false claim led to the resignation of George Entwistle as Director-General of the BBC on 10 November 2012.
Silvio Marić is a Croatian former footballer who played as an attacking midfielder. Born in Zagreb, Marić began his professional career at Dinamo Zagreb in 1992. In the autumn of 1998, he appeared for Dinamo Zagreb in all of their six group matches in the UEFA Champions League and secured himself a move to English club Newcastle United on 4 February 1999 for a transfer fee of $5.8 million. He made his Premier League debut for Newcastle United on 10 March 1999 against Nottingham Forest, but never established himself as a regular in the side and, after making 23 Premier League appearances without scoring, moved to Portuguese club Porto in 2000. At Newcastle United, he was the first Croatian player to appear in an FA Cup Final, when he came on as a substitute in the Magpies' 2–0 defeat to Manchester United in the 1999 Final. During the final, with Newcastle trailing 2–0, Marić weakly shot past the post when exceptionally well placed to score; this summed up his Newcastle career in general. He did, score twice for Newcastle in their 1999-2000 UEFA Cup campaign, when he netted both home and away against Zürich.
After playing one season for Porto, where he never became a regular, he made his first comeback to Dinamo Zagreb and subsequently spent two seasons with the club before making another move abroad, to Greek club Panathinaikos in 2003. He subsequently spent two seasons at Panathinaikos and made nine UEFA Champions League appearances for the club before making his second comeback to Dinamo Zagreb in 2005, signing a two-year contract. However, with his role in the team diminished and the fact that he appeared as a substitute, he cancelled his contract upon the end of the 2005–06 season and thus finished his playing career. In his three spells with Dinamo, he appeared in a total of 146 league scored 41 goals. Marić made his international debut for the Croatian national team on 30 April 1997 in their 1998 FIFA World Cup qualifier against Greece and scored his first international goal in his second cap against Bosnia and Herzegovina on 6 September 1997 in this same qualifying session. Between 1995 and 1997, he made several appearances for the Croatian national under-21 team.
He was a member of the Croatian squad that won the bronze medal at the 1998 FIFA World Cup finals in France and appeared in four matches at the tournament, although he only started the final group match against Argentina. He won a total of 19 international caps for Croatia between 1997 and 2002, but his first international goal remained his only one, his last appearance for the Croatian national team came on 12 October 2002 in their second Euro 2004 qualifier, which they lost 2–0 to Bulgaria on the road. Dinamo Zagreb Prva HNL: 1992–93, 1995–96, 1996–97, 1997–98, 2002–03, 2005–06 Croatian Cup: 1996, 1997, 1998, 2002 Croatian Supercup: 2002Porto Taça de Portugal: 2001Panathinaikos Super League Greece: 2003–04 Greek Cup: 2003–04 Order of the Croatian Interlace - 1998 Silvio Marić – FIFA competition record Silvio Marić at National-Football-Teams.com