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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.
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.
Many repeat sequences are likely to be non-functional, decaying remnants of Transposable elements, these have been labelled "junk" or "selfish" DNA. [7] [8] [9] Nevertheless, occasionally some repeats may be exapted for other functions. [10]
A single-stranded non-circular DNA molecule has two non-identical ends, the 3' end and the 5' end (usually pronounced "three prime end" and "five prime end"). The numbers refer to the numbering of carbon atoms in the deoxyribose, which is a sugar forming an important part of the backbone of the DNA molecule. In the backbone of DNA the 5' carbon ...
The A form occurs under non-physiological conditions in partly dehydrated samples of DNA, while in the cell it may be produced in hybrid pairings of DNA and RNA strands, and in enzyme-DNA complexes. [54] [55] Segments of DNA where the bases have been chemically modified by methylation may undergo a larger change in conformation and adopt the Z ...
In 1977, work by the Sharp and Roberts labs revealed that genes of higher organisms are "split" or present in several distinct segments along the DNA molecule. [2] [3] The coding regions of the gene are separated by non-coding DNA that is not involved in protein expression.
Although DNA is a double-stranded molecule, typically only one of the strands encodes information that the RNA polymerase reads to produce protein-coding mRNA or non-coding RNA. This 'sense' or 'coding' strand, runs in the 5' to 3' direction where the numbers refer to the carbon atoms of the backbone's ribose sugar.
The split gene theory is a theory of the origin of introns, long non-coding sequences in eukaryotic genes between the exons. [1] [2] [3] The theory holds that the randomness of primordial DNA sequences would only permit small (< 600bp) open reading frames (ORFs), and that important intron structures and regulatory sequences are derived from stop codons.