Nucleic acids, biochemical compounds that control the structure of proteins. The first nucleic acid was detected in the late 1860s by Swiss F. Miescher, who isolated it from the cell nucleus. The compound reacted acid and was soluble in base. It was called nucleic acid, a name who is still used, although the nucleic acids have also been found in the cell cytoplasm.
Dividing the nucleic acids in two main groups: deoxyribonucleic acid, DNA and ribonucleic acid RNA. DNA is found mainly in the nucleus, but also in the cytoplasm mitochondria and chloroplasts, while the RNA preferentially found in the cytoplasm.
Nucleic acids are straight chain polymers, i.e the molecules are long chains made up of the same units. A protein is a polymer (polypeptide) with amino acids as building blocks. Similarly, nucleic acid's polynucleotide composed of nucleotides, and thus comes to consist of equal parts of pentose, phosphoric acid and an organic base. Nicely, Osen is ribose in RNA and deoxyribose in DNA. The four common bases are purinderivatene adenine and guanine, and thymine pyrimidinderivatene, uracil and cytosine. Thymine is found at most in DNA, uracil only in RNA. Nucleotides in the nucleic acid bound together by phosphoric acid molecules, which are testifier to the hydroxyl group at carbon atom 3 in one attractive mouth and the carbon atom 5 in the next pretty mouth. Chromosomes can be DNA molecules of several hundred million joints.
Genes and DNA structure
There was early aware of the genetic systems was associated with something in the cell nucleus, but only around 1950, attempts were made, which showed that the nucleic acids were carriers of the gene. It was such. Shown that when certain virus species, bacteriophages, attack bacteria and reproduce in them, only the DNA molecule from the attacker to penetrate the bacterial cell. The information transmitted from generation to generation, is, in other words, DNA molecules, encoded as a sequence of nucleotides. A gene is therefore, identical to a piece of a DNA molecule.
In 1953 JD Watson and Crick HC concluded that the DNA molecules consist of two polynucleotides which are twisted about each other into a double helix. Bases facing the axis, so that the basis of the two chains in pairs are in contact with each other via hydrogen bonds. Space and binding conditions in helix strukturen allow only two types of such base contacts, namely adenine (A) with thymine (T) and guanine (G) with cytosine (C). In higher organisms, we find that the DNA is bound to proteins, mainly histones. Histones form complexes such as DNA wrapped around. During cell division, there is a further strong oppkveiling of DNA molecules, so they are visible in the light microscope.
The spatial structure of DNA that Watson and Crick discovered, could, as they themselves pointed out, in a simple way to explain how the DNA molecule is replicated in principle. Consider Mon dobbelt heliksen, one sees that the two strands of helix correspond to each other. Is the base sequence in one strand given, then it is thus given also for the other. Base pairing rules determines the way the base in one strand is facing a given base in the other thread. We say that the strands are complementary.
Replication starts by hydrogen bonds between the two single strands of DNA are broken locally. New poly deoxyribonucleic kjeder formed by the enzyme DNA polymerase from the four deoksiribonukleik-triphosphate during disconnection of pyrophosphate. Step by step synthesized two new poly deoksyribonukleotid kjeder, complementary to the two original DNA strands, which here acts as template (model, mold). As the synthesis progresses, it will open new areas of DNA dobbelt heliksen. Finally, one has got two new dobbelt heliksen that are identical to each other, and identical with the original dobbelt heliksen. This form of DNA synthesis is called semi-conservative replication, because each of the two daughter DNA dobbelt heliksen contains a newly synthesized DNA strand and a DNA strand from the original DNA dobbelt heliksen. Replication by this model will also ensure separation of the new DNA dobbelt heliksen. The process is actually much more complicated. The participating proteins that help opptvinning of the spiral. DNA synthesis occurs in the form of bits that are later connected. Prior to this synthesis is the synthesis of an RNA-bit, a primer, which forms the starting point for DNA synthesis. This RNA then removed and replaced with DNA.
Bacteria have ring-shaped DNA molecules of approx. 4 million base pairs, where replikering start at a particular place and propagate in both directions. In higher organisms, there are several starting points in each DNA molecule, which is required for all DNA will prefer to be duplicated before the cell divides. Parts of the enzyme apparatus involved in replikering grabs also, together with certain other enzymes, when DNA molecules are damaged due to incorrect copying, radiation or chemicals. Hereby reduces the possibility of mutations, tumors or cell death.
RNA, the formation and function
RNA found in cells as a single-polymers. It is formed by a similar process of DNA replication by the so-called transcription. One of the DNA strands in a double helix serves as template together with the enzyme RNA polymerase and the four ribonucleoprotein adenosine, guanosine, cytidine and uridintrifosfat. RNA polymerase is DNA dobbelt heliksen to open up temporarily in a small area. In all cells formed three main types of RNA:
Messenger RNA, mRNA (messenger RNA), contains information on amino acid sequence of the different proteins.
Ribosomal RNA, rRNA, a group of RNA molecules that are involved in building up the cell protein synthetiseren apparatus, ribosomes.
Truck-RNA, tRNA, participates in protein synthesis by the amino acids to the ribosomes.
MRNA and rRNA are high-molecular compounds with from a few hundred to several thousand nucleotides, while the tRNA has approx. 80 nucleotides in the chain. Information decline in the cell is shown in the diagram (Fig. 1).
The synthesis of proteins on ribosomes, conducted by the mRNA is called translation (translation) because it is happening is a translation of the information that is available as a nucleotide sequence in DNA and mRNA into a amino acid number in a similar polypeptide. One polynucleotides respond directly to the polypeptide chain, allowing a group of 3 nabonukleotider, a codon, codes for one amino acid.
In this translation process, tRNA molecules play a key role. A tRNA molecule is so designed that it is associated with a particular amino acid at one end. At the other end is a loop, anticodon loop, which is complementary to the amino acid codon. When this codon in the mRNA comes to reading the ribosome, the correct amino acid is held fixed, via its tRNA, as with anticodon loop form AU-and GC-base pairs with the codons. (U in RNA has the same properties as T in DNA.) A tRNA molecule with the anticodon AAA will then bind to the mRNA when tripletten IUU should be read. The peptide bond is formed as the nano amino syren, held in position by the tRNA.
In addition to these classical families RNA, rRNA, mRNA and tRNA, the recent research has shown that it also formed RNA molecules with very different functions. RNA molecules are included in spliceosome which accounts for the removal of introns described above, see also RNA splicing . Both ribosomes and spliceosome RNA molecules play an active, catalytic role corresponding to the protein plays in most other processes in the cell, see ribozymes . Small RNA molecules is also shown to influence the regulation of gene activity at all levels, both in the reading of genes, the lifetime of the mRNA formed during the reading, and the efficiency of the ribosome synthesis of proteins with mRNA as a template. See the anti-sense oligonucleotides and RNA interference . Dual role of RNA molecules plays, both carriers of genetic information and molecules with the ability to catalyze biological processes, has led many to assume that RNA must have played a central role in early evolution, the so-called "RNA world hypothesis" .
Degradation of nucleic acids
Unless there is a matter of growing cells, the synthesis of nucleic acids is balanced by a corresponding deterioration. Nucleic acids attacked by exo-and endonucleases, attacking respectively from the end and inside the molecules. They produce less polynucleotides and free nucleotides. Nucleotidase liberate phosphoric acid from nucleotides, and finally removed pretty mouth. Nucleic acids that are taken into the food, degrade in a similar way by enzymes in the digestive tract.