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Non-B DNA can have significant implications for DNA biology and human health. For example, Z-DNA has been implicated in immunity and autoimmune diseases, such as lupus and arthritis. [6] H-DNA has been implicated in genomic instability and cancer, and G-quadruplexes have been linked to telomere maintenance, [7] oncogene activation, and cancer. [8]
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 ...
Non-functional DNA is rare in bacterial genomes which typically have an extremely high gene density, with only a few percent being not protein-coding. [60] However, in most animal or plant genomes, a large fraction of DNA is non-functional, given that there is no obvious selective pressure on these sequences.
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 a type of junk DNA. Most non-bacterial genomes contain many pseudogenes, often as many as functional genes. This is not surprising, since various biological processes are expected to accidentally create pseudogenes, and there are no specialized mechanisms to remove them from genomes.
A comprehensive study of DNA sequences from multiple human samples inferred the existence of 4,930 species of microbes of which 77% were previously unreported. [33] Health-related findings include a prophage that might be associated with cirrhosis of the liver , [ 27 ] and seven novel sequences from children with type-1 diabetes that have ...
DNA sequences that carry the instructions to make proteins are referred to as coding sequences. The proportion of the genome occupied by coding sequences varies widely. A larger genome does not necessarily contain more genes, and the proportion of non-repetitive DNA decreases along with increasing genome size in complex eukaryotes. [38]
Mitochondrial DNA is a small portion of the DNA contained in a eukaryotic cell; most of the DNA is in the cell nucleus, and, in plants and algae, the DNA also is found in plastids, such as chloroplasts. [3] Human mitochondrial DNA was the first significant part of the human genome to be sequenced. [4]