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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.
A non-coding RNA (ncRNA) is a functional RNA molecule that is not translated into a protein. The DNA sequence from which a functional non-coding RNA is transcribed is often called an RNA gene. Abundant and functionally important types of non-coding RNAs include transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), as well as small RNAs such as ...
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 ...
For example, only about 1.5% of the human genome consists of protein-coding exons, with over 50% of human DNA consisting of non-coding repetitive sequences. [98] The reasons for the presence of so much noncoding DNA in eukaryotic genomes and the extraordinary differences in genome size , or C-value , among species, represent a long-standing ...
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]
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.
Antisense oligonucleotides can be used to target a specific, complementary (coding or non-coding) RNA. If binding takes place this hybrid can be degraded by the enzyme RNase H. [12] RNase H is an enzyme that hydrolyzes RNA, and when used in an antisense oligonucleotide application results in 80-95% down-regulation of mRNA expression. [6]
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.