Нуклеинске киселине

Поређење две главне нуклеинске киселине: РНК (лево) и ДНК (десно)

Шематски приказ структуре ДНК: жути кругови представљају фосфате, зелени дезоксирибозу, а црвени азотне базе;пуном цртом представљена је ковалентна веза, а испрекиданом водонична

Нуклеинске киселине су крупни и сложени органски молекули значајни за ћелију и одговорни за најзначајније процесе, као што су наслеђивање, синтеза протеина, у њој. Постоје два типа нуклеинских киселина: дезоксирибонуклеинска киселина и рибонуклеинска киселина. ДНК је носилац наследних информација у ћелији, док РНК учествују у преношењу тих информација и њиховом превођењу у протеине. Нуклеинске киселине су макромолекули чију јединицу грађе представљају нуклеотиди. Њих образује један пентозни шећер за који је везана фосфатна група и једна азотна, пуринска или пиримидинска база. Нуклеотиди међусобно повезују и на тај начин, захваљујући вези која се успоставља између фосфата и шећера, формирају ланац. Осим у вирусима, који садрже једну или другу нуклеинску киселину (никада обе), ДНК и РНК се налазе у свим врстама организама. Нуклеинске киселине се највише налазе у једру (lat. nucleus) па су по томе и добиле назив. Први их је изоловао Фридрих Мишер 1872. године. Нешто касније установљено је да се, осим у једру, налазе и у цитоплазми. Према данашњим подацима познато је да засебне нуклеинске киселине садрже и неке од ћелијских органела, какве су нпр. митохондрије и хлоропласти. Према грађи су полимери изграђени од мономера - нуклеотида.

У изградњи нуклеотида, који формирају ДНК учесвују:

• пентозни шећер дезоксирибоза,
• пуринске (деривати пурина) базе аденин и гуанин, или приримидинске(деривати пиримидин) базе цитозин и тимин
• киселински остатак фосфорне киселине.

У изградњи нуклеотида РНК учесвују:

• пентозни шећер рибоза,
• пуринске (деривати пурина) базе аденин и гуанин, или приримидинске(деривати пиримидина) базе цитозин и урацили
• киселински остатак фосфорне киселине.

Nucleic acids are naturally occurring chemical compounds that serve as the primary information-carrying molecules in cells and makeup the genetic material. Nucleic acids are found in abundance in all living things, where they create, encode, and then store information of every living cell of every life-form on Earth. In turn, they function to transmit and express that information inside and outside the cell nucleus to the interior operations of the cell and ultimately to the next generation of each living organism. The encoded information is contained and conveyed via the nucleic acid sequence, which provides the 'ladder-step' ordering of nucleotides within the molecules of RNA and DNA. They play an especially important role in directing protein synthesis.

Strings of nucleotides are bonded to form helical backbones—typically, one for RNA, two for DNA—and assembled into chains of base-pairs selected from the five primary, or canonical, nucleobases, which are: adenine, cytosine, guanine, thymine, and uracil. Thymine occurs only in DNA and uracil only in RNA. Using amino acids and the process known as protein synthesis, the specific sequencing in DNA of these nucleobase-pairs enables storing and transmitting coded instructions as genes. In RNA, base-pair sequencing provides for manufacturing new proteins that determine the frames and parts and most chemical processes of all life forms.

Историја

The Swiss scientist Friedrich Miescher discovered nucleic acids (DNA) in 1868. Later, he raised the idea that they could be involved in heredity.

• Nuclein were discovered by Friedrich Miescher in 1869 at the University of Tübingen, Germany.
• In the early 1880s Albrecht Kossel further purified the substance and discovered its highly acidic properties. He later also identified the nucleobases.
• In 1889 Richard Altmann creates the term nucleic acid
• In 1938 Astbury and Bell published the first X-ray diffraction pattern of DNA.
• In 1944 the Avery–MacLeod–McCarty experiment showed that DNA is the carrier of genetic information.
• In 1953 Watson and Crick presented the structure of DNA.

Experimental studies of nucleic acids constitute a major part of modern biological and medical research, and form a foundation for genome and forensic science, and the biotechnology and pharmaceutical industries.

Појава и номенклатура

The term nucleic acid is the overall name for DNA and RNA, members of a family of biopolymers, and is synonymous with polynucleotide. Nucleic acids were named for their initial discovery within the nucleus, and for the presence of phosphate groups (related to phosphoric acid). Although first discovered within the nucleus of eukaryotic cells, nucleic acids are now known to be found in all life forms including within bacteria, archaea, mitochondria, chloroplasts, and viruses (There is debate as to whether viruses are living or non-living). All living cells contain both DNA and RNA (except some cells such as mature red blood cells), while viruses contain either DNA or RNA, but usually not both. The basic component of biological nucleic acids is the nucleotide, each of which contains a pentose sugar (ribose or deoxyribose), a phosphate group, and a nucleobase. Nucleic acids are also generated within the laboratory, through the use of enzymes (DNA and RNA polymerases) and by solid-phase chemical synthesis. The chemical methods also enable the generation of altered nucleic acids that are not found in nature, for example peptide nucleic acids.

Молекуларни састав и величина

Nucleic acids are generally very large molecules. Indeed, DNA molecules are probably the largest individual molecules known. Well-studied biological nucleic acid molecules range in size from 21 nucleotides (small interfering RNA) to large chromosomes (human chromosome 1 is a single molecule that contains 247 million base pairs).

In most cases, naturally occurring DNA molecules are double-stranded and RNA molecules are single-stranded. There are numerous exceptions, however—some viruses have genomes made of double-stranded RNA and other viruses have single-stranded DNA genomes, and, in some circumstances, nucleic acid structures with three or four strands can form.

Nucleic acids are linear polymers (chains) of nucleotides. Each nucleotide consists of three components: a purine or pyrimidine nucleobase (sometimes termed nitrogenous base or simply base), a pentose sugar, and a phosphate group which makes the molecule acidic. The substructure consisting of a nucleobase plus sugar is termed a nucleoside. Nucleic acid types differ in the structure of the sugar in their nucleotides–DNA contains 2'-deoxyribose while RNA contains ribose (where the only difference is the presence of a hydroxyl group). Also, the nucleobases found in the two nucleic acid types are different: adenine, cytosine, and guanine are found in both RNA and DNA, while thymine occurs in DNA and uracil occurs in RNA.

The sugars and phosphates in nucleic acids are connected to each other in an alternating chain (sugar-phosphate backbone) through phosphodiester linkages. In conventional nomenclature, the carbons to which the phosphate groups attach are the 3'-end and the 5'-end carbons of the sugar. This gives nucleic acids directionality, and the ends of nucleic acid molecules are referred to as 5'-end and 3'-end. The nucleobases are joined to the sugars via an N-glycosidic linkage involving a nucleobase ring nitrogen (N-1 for pyrimidines and N-9 for purines) and the 1' carbon of the pentose sugar ring.

Non-standard nucleosides are also found in both RNA and DNA and usually arise from modification of the standard nucleosides within the DNA molecule or the primary (initial) RNA transcript. Transfer RNA (tRNA) molecules contain a particularly large number of modified nucleosides.

Литература

• Wolfram Saenger, Principles of Nucleic Acid Structure, 1984, Springer-Verlag New York Inc.
• Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter Molecular Biology of the Cell. 2007. ISBN 978-0-8153-4105-5. Fourth edition is available online through the NCBI Bookshelf: link
• Jeremy M Berg, John L Tymoczko, and Lubert Stryer, Biochemistry 5th edition, 2002, W H Freeman. Available online through the NCBI Bookshelf: link
• Astrid Sigel; Helmut Sigel; Roland K. O. Sigel, ур. (2012). Interplay between Metal Ions and Nucleic Acids. Metal Ions in Life Sciences. 10. Springer. ISBN 978-94-007-2171-5. doi:10.1007/978-94-007-2172-2. 
• Palou-Mir, Joana; Barceló-Oliver, Miquel; Sigel, Roland K.O. (2017). „Chapter 12. The Role of Lead(II) in Nucleic Acids”. Ур.: Astrid, S.; Helmut, S.; Sigel, R. K. O. Lead: Its Effects on Environment and Health. Metal Ions in Life Sciences. 17. de Gruyter. стр. 403—434. PMID 28731305. doi:10.1515/9783110434330-012. 

Спољашње везе

• Бионет школа
• Interview with Aaron Klug, Nobel Laureate for structural elucidation of biologically important nucleic-acid protein complexes provided by the Vega Science Trust.
• Nucleic Acids Research (Journal)
• Nucleic Acids Book (free online book on the chemistry and biology of nucleic acids)