DNA has two basic functions:
1) it determines the properties of the cell that directs the structure of all proteins, among which the enzymes that provide virtually all the chemical processes in the cell and
2) the transfer of these properties to the cell's genetic offspring when the cell divides.
The DNA contains all of our genes. Only in 1952 was the final proof that there is DNA and protein make up the hereditary material and specific genetic characteristics were related to precise parts of this molecule. DNA structure was described by the American biochemist James Dewey Watson (born 1928) and the British Biophysicists Francis Crick Harry Compton (1916-2004) in 1953. These findings represented the start of a long series of breakthroughs in genetics, and the study was the beginning of modern genetics and gene technology. DNA found in the nucleus of eukaryotic organisms. In addition to this, the mitochondria 's own DNA.
Structure DNA's, such as RNA , a nucleic acid ("acid core" of lazy. nucleus 'core', the designation of the nucleus). The molecule is built up as long chains of smaller units called nucleotides. In a DNA molecule enters into the four different nucleotides. A nucleotide consists of a phosphoric acid and a specific carbohydrate (deoxyribose). In addition, a nitrogenous base that can be either adenine, cytosine, guanine and thymine, commonly abbreviated A, C, G and T. The amino acid in a nucleotide is linked to carbohydrate in the next, so that the links in the chain alternately consisting of phosphoric acid and carbohydrate, forming a "sugar phosphate backbone." The bases are linked to carbohydrate. A DNA molecule is normally made up of two such chains, which are turned into a right-rotating double helix around a common axis.
In the inner spiral, the two chains are held together by the so-called hydrogen bonds between bases located opposite each other. The bases are paired not accidental. Above an adeninbase in one chain, is it always a thyminbase in the other. In the same way guanine paired with cytosine always. This base pairing principle forms the basis of all the features of DNA.
Double spiral - or dual helix that is often called - can be compared to a spiral staircase where the steps consist of the paired bases. The bases in the DNA molecule form four different "steps" in the twice helix: AT, TA, GC and CG. DNA molecule in a human cell consists of approx. three billion (3 × 10 9) such steps, and their sequence may vary indefinitely.
Genes The part of the DNA molecule that contains information about a gene, called a gene. DNA, or DNA amount, in a human cell weighs 7.3 × 10 -12 grams (0.000 000 000 0073 grams) and measures a total of 220 cm if it is extended. It must be packed very tightly to fit in the cell nucleus. This occurs when the DNA coils around special packaging proteins (histones). The function of DNA is closely associated with the molecular structure as mentioned above. Most genes whose task is to determine the composition of protein molecules. One gene acts as recipe for a particular protein. It is estimated that the genetic material in humans (the human genome) contains less than 30 000 genes that code for proteins.
The proteins are composed of long chains of amino acids (see proteins ), and it is the order of these different amino acids that determine the form, and thus the behavior, the various proteins. There are four distinctive "steps" in the DNA molecule, where the order can be combined freely. When dealing with a single strand of DNA molecule, forming the four different steps (nucleotides) a sequence of letters A, G, C and T. The information about the DNA molecule is in the order (sequence) of these nucleotides, so the order of letters forming words in a written language. A piece of DNA that has a specific sequence (nucleotide sequence) will determine aminosyrerekkefolgen in a particular protein. In this way, the sequence of nucleotides in the cell's DNA together described all the proteins that the cell can produce.
Since the DNA structure determines protein structure, there must be a direct link between the steps, ie nukleotidrekkefolgen in DNA and proteins in aminosyrerekkefolgen. Because there are 20 different amino acids, this wiring diagram had at least 20 dissimilar orders. In addition, it must contain as many orders as the number of amino acids found in each protein. Since there are further than four steps in the DNA molecule, a single order consists of more than one step. With two stages of each order can the four steps to create 4 × 4 = 16 different orders. So there is not sufficient with two steps to create an order. If an order on the other hand consists of three steps, one can construct the 4 × 4 × 4 = 64 orders or codeword. Since there are more code words than you strictly need, there are several code words for each amino acid. Such spare codes reduces the risk of genetic errors. This wiring diagram between code words on the DNA molecule and the various amino acids is called the genetic code.
The code word is read not as a whole step or base pairs, but the sequence of bases in one strand in the helix. The steps AT, GC, GC will, for instance. give the code word AGG. Such a code word of three nucleotides called a codon .
Protein synthesis Most of the cell's DNA found in the nucleus (nucleic acid does not really core acid). The cell builds up its proteins called ribosomes in the cytoplasm. DNA instructions must be transferred from the nucleus to the ribosomes, where protein synthesis takes place. This is done by using another type of nucleic acid called ribonucleic acid or RNA (the meadow. Ribonucleic acid).
RNA is constructed as DNA, but the deoxyribose is replaced with another carbohydrate, ribose. In addition, thymine (T) replaced by another base, uracil (U). In the same way as thymine, uracil, however, only can pair with adenine.
The synthesis of a protein starts with the DNA-instructions for this protein are copied in the form of an RNA molecule. This process - called transcription - carried out by means of base pairing. First break the hydrogen bonds between the bases in that part of the DNA helix that encodes for the protein, so that the double helix is opened. Then enzymes assemble an RNA molecule by using the order in one of the threads in the DNA molecule as a "recipe". RNA is uracil in which DNA has adenine, cytosis in which DNA has guanine, etc. Eg. is a DNA codon TTA that transcribed the AAU in the RNA copy.
There are several forms of RNA. The form that brings the coded instructions from the nucleus to a ribosome, called mRNA ("m" stands for eng. Messenger, 'messenger'). These are relatively large molecules, for they shall contain three nucleotides for each amino acid that is part of the protein. The structure of the protein in the ribosome involved a type of small RNA molecules called tRNA ("t" stands for eng. Transfer, 'transfer'). tRNA is located in the cytoplasm and transports amino acids up to the ribosome. A given tRNA molecule can bind only with one type of amino acid. tRNA molecule is equipped with an anticodon, a sequence of three nucleotides which is compatible with (is complementary to) a codon in the mRNA molecule. In this way, the tRNA molecules that "read" the pattern of mRNA, linking nucleotide sequence of the mRNA with aminosyrerekkefølgen of the protein. There are not as many different tRNA molecules as there are codons, as some tRNA molecules tolerate deviations in position three of codon.
Protein synthesis takes place while the ribosome moves along the mRNA molecule. One by one amino acids are linked together in the correct order, dictated by the order to "code words" in the RNA molecule.
Cell division Before a cell can divide, it must make copies of their DNA molecules so that the two new cells can be equipped with the same code instructions and build the same proteins as morcellen. This process is called replication, and also the place of base pairing.
First break the hydrogen bonds between the bases. Then rotate the double helix about its axis so that the two chains are wound from one another and appear as single chains. By using the old single chain pattern chain enzymes with a new DNA single chain to form two double spirals. Each of them consists of an old and a new chain. The nucleotide sequence of the new chain is due baseparingen "reverse identical" or complementary to the old one. Because the sequence of the old thread determines the exact sequence of the new cells can produce exact copies of genetic material, so that genetic characteristics can be passed from cell to cell.
Arts Development The genetic code is universal, meaning that the code is almost identical in all living organisms, from the simplest virus to humans. In some viruses the genetic material bearing RNA and not DNA, but the code is the same. When an RNA virus infects a cell, it can in the same way as DNA viruses use the chemical apparatus in the cell, and manufacture their own proteins. This code will probably not be encountered more than once in the history of life, may be inferred that all the organisms that live or have lived on Earth have a common origin at the molecular level.
The amount of DNA in the cells varies from species to species, but it is the same in all cells in individuals of the same species. (In gametes, which have half the chromosome number, however, the amount of DNA cut in half). One can use DNA analysis to detect relationships between species, eg. between different bacteria.
All cells of higher organisms have arisen from one fertilized egg cell. In these multicellular organisms are many different cell types, with very different functions. All these cells have the same composition of DNA (the same nucleotide sequence), but are different because they do not actively reading of (transcribe) the same set of genes. Different cells thus consists of various kinds of proteins. Also the distribution of different cell types and the way these types of cell builds up the organism is determined by the nucleotide sequence in DNA.
DNA replication is a conservative process that seeks to preserve the genetic material unchanged. The large number of species found, however, show that billions of years has caused countless "mistakes" when it comes to preserving the genetic material unchanged. These errors are called mutations . In real terms is very useful mutations, since they are a prerequisite for a development can take place. Without them life would not be able to adapt to new conditions.
There are different categories of mutations. Replacement of enkeltnukleotider, called point mutations. At the simplest is a base pair modified or replaced with another. This does not have to have major consequences. Far more serious is it if it is introduced or removed one or two nucleotides in a sequence. It results in the "rhythm" in the interpretation of the sequence is shifted, since codon read three and three in the hallway. The gene will then be read incorrectly. Such mutations will often be deadly in the offspring because the formation of a protein can not perform its function eg. in cellular metabolism.
A large number of hereditary diseases caused by enzyme defects that can be traced back to errors in the DNA code. This error stems from the egg or the sperm that became the fertilized egg. Such errors are then passed on to all the cells in the body. This is the reason that we still only have little opportunity to cure diseases caused by enzyme defects. Examples include a wide range of metabolic diseases, eg. phenylketonuria (Foaling disease).
Mutations derived from germ cells will be inherited from generation to generation. Mutations can also affect body cells and they are called somatic. Somatic mutations are not passed down from generation to generation, but extending to all descendants of that cell that was affected by the mutation. Such somatic mutations are common in cancer and the molecular cause of the cancer occurs.