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The common theme is that the original proponents of junk DNA thought that all non-coding DNA was junk. [2] [6] This claim has been attributed to a paper by David Comings in 1972 [28] where he is reported to have said that junk DNA refers to all non-coding DNA. [19] But Comings never said that.
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. [31]
Satellite DNA consists of very large arrays of tandemly repeating, non-coding DNA. Satellite DNA is the main component of functional centromeres , and form the main structural constituent of heterochromatin .
Antisense transcripts are stretches of non coding mRNA that are complementary to the coding sequence. [7] Genome wide studies have shown that RNA antisense transcripts occur commonly within nature. They are generally believed to increase the coding potential of the genetic code and add an overall layer of complexity to gene regulation.
Other segments of DNA are transcribed into RNA molecules called non-coding RNAs (ncRNAs). Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.
Long non-coding RNA/lncRNA: Non-coding RNA transcripts that are more than 200 nucleotides long. Members of this group comprise the largest fraction of the non-coding transcriptome other than introns. It is not known how many of these transcripts are functional and how many are junk RNA. transfer RNA/tRNA; micro RNA/miRNA: 19-24 nucleotides (nt ...
The non-intron sequences that become joined by this RNA processing to form the mature RNA are called exons. [3] Introns are found in the genes of most eukaryotes and many eukaryotic viruses, and they can be located in both protein-coding genes and genes that function as RNA (noncoding genes). There are four main types of introns: tRNA introns ...
De novo gene birth is the process by which new genes evolve from non-coding DNA. [ 1 ] [ 3 ] De novo genes represent a subset of novel genes, and may be protein-coding or instead act as RNA genes. [ 4 ]