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13. Definere begreberne kodende og "junk" områder i DNA sekvenser
Devlin, s.74
http://www.psrast.org/junkdna.htm

The human genome codes for ca. 35000 genes.

Only 2-4% of DNA in mammalian cells codes for structural genes.
Some of the remaining DNA (2-3%) is found in telomeres, centromeres and DNA sequences that code for RNA.  

Over 95% of DNA has largely unknown function. It was called "junk-DNA" because molecular biologist weren’t able to ascribe any function to it. It was assumed to be molecular garbage. The idea that a major part of our DNA is "garbage" ignored the fact that a key feature of biologic organisms is optimal energy expenditure. To carry enormous amounts of unnecessary molecules is contrary to this fundamental energy saving feature of biological organisms.

If the non-coding DNA is mostly molecular garbage, then it should have had a completely random bas sequences. This is not the case.

Increasing evidence is now indicating many important features of junk DNA:

• junk DNA plays a vital role in the regulation of gene expression during embrionic development

• junk DNA enhances the transcription of proximal genes (genes close to the respective DNA)

• junk DNA acts as silencer for suppression of transcription of proximal genes

• junk DNA regulates translation of proteins 

Still, there is a little knowledge about the relationship between junk DNA and coding DNA. This adds to other factors making it impossible to foresee and control the effect of artificial insertion of foreign genes, fx. gene therapy.

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