Noncoding DNA

As a non-coding deoxyribonucleic acid (English noncoding DNA, formerly junk DNA ) are those parts of the deoxyribonucleic acid ( DNA) are called that do not code for proteins. In higher organisms such as humans, animals and plants, the vast majority of the DNA in this sense " non-coding ". But these portions of the DNA have various functions.

Occurrence

Protein -encoding DNA is used as a template for messenger RNA which is in turn used in the synthesis of the protein as a template. The former is referred to as transcription, translation of the latter as. And non- coding DNA regions are transcribed frequently, the resulting RNAs are not used for the translation ( non-coding RNA ). Classic long-known examples are the ribosomal and transfer RNA, both of which have essential functions also in the translation, but do not serve as a template.

Non-coding DNA is especially characteristic of eukaryotes, where it accounts for the largest portion of the genome, whereas its share in prokaryotic genomes is only 5-20%.

In human DNA are currently about 95 % of the nucleotides are considered as non-coding DNA, which means that a maximum of 5 % of the nucleotides from which the DNA is encoding genetic information for proteins. The ENCODE project, in which the functional elements of the genome to be described, has come to the conclusion that these areas are nevertheless transcribed in large part, are thus transcribed into RNA. A new study contradicts this finding, however, and comes to the conclusion that noncoding regions are virtually non- transcribed.

Examples

Widely used are the so-called pseudo- genes, copies of genes, which are no longer functional due to mutation. They are considered in the context of evolutionary theory as a starting material for new genes with new functions.

Significant portions of the noncoding DNA make repetitive sequences, which consist of numerous repetitions of a base sequence.

And regular genes contain non-coding sections: the promoter region, which serves for the regulation of the activity of the gene ( gene expression ), and introns which, although transcribed by whose transcripts are, however, removed before translation ( splicing ). Other non-coding DNA segments that are not constituents of genes themselves, but involved by interacting with promoters in the regulation of gene expression, are the enhancers and silencers.

Non-coding further are telomeres, the ends of the chromosomes.

Functions

Today it is largely unknown how large the proportion of non-coding DNA, which fills a function. For the majority of non-coding DNA is unknown whether to get their functional tasks. For their dispensability speaks to a study, was removed at the two longer stretches of noncoding DNA from the genome of mice, which resulted in no appreciable differences in the phenotype.

A distinction is made ​​between a direct function in the body and a long-term evolutionary significance. Some types of non-coding DNA such as pseudogenes or transposable elements have played an important role in evolution, even if they fill no immediate function.