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The nonfunctional DNA in bacterial genomes is mostly located in the intergenic fraction of non-coding DNA but in eukaryotic genomes it may also be found within introns. There are many examples of functional DNA elements in non-coding DNA, and it is erroneous to equate non-coding DNA with junk DNA.
Pseudogenes are nonfunctional segments of DNA that resemble functional genes.Pseudogenes can be formed from both protein-coding genes and non-coding genes. In the case of protein-coding genes, most pseudogenes arise as superfluous copies of functional genes, either directly by gene duplication or indirectly by reverse transcription of an mRNA transcript.
Junk DNA (non-functional DNA) is a DNA sequence that has no known biological function. [ 1 ] [ 2 ] Most organisms have some junk DNA in their genomes —mostly, pseudogenes and fragments of transposons and viruses—but it is possible that some organisms have substantial amounts of junk DNA.
First generation (blue) where annotators used ab initio methods at a local scale, second generation (red) with genome-wide ab initio methods, third generation (green) characterized by a combination of ab initio methods and homology-based annotations, and the fourth generation (orange) in which an approach to identification of the non-coding ...
Exonucleases remove these unpaired nucleotides and the gaps are filled by DNA synthesis and repair machinery. [1] [3] Exonucleases may also cause shortening of this junction, however this process is still poorly understood. [4] Junctional diversity is liable to cause frame-shift mutations and thus production of non-functional proteins ...
Non-functional DNA elements such as pseudogenes and repetitive DNA, both of which are types of junk DNA, can also be found in intergenic regions—although they may also be located within genes in introns. [2] It is possible that these regions contain as of yet unidentified functional elements, such as non-coding genes or regulatory sequences. [3]
However, some DNA sequences that do not code protein may still encode functional non-coding RNA molecules, which are involved in the regulation of gene expression. [100] T7 RNA polymerase (blue) producing an mRNA (green) from a DNA template (orange) [101] Some noncoding DNA sequences play structural roles in chromosomes.
Gene structure is the organisation of specialised sequence elements within a gene.Genes contain most of the information necessary for living cells to survive and reproduce. [1] [2] In most organisms, genes are made of DNA, where the particular DNA sequence determines the function of the gene.