intron
in·tron
I0208950 (ĭn′trŏn)intron
(ˈɪntrɒn)in•tron
(ˈɪn trɒn)n.
| Noun | 1. | intron - sequence of a eukaryotic gene's DNA that is not translated into a protein |
| 单词 | intron | |||
| 释义 | intronin·tronI0208950 (ĭn′trŏn)intron(ˈɪntrɒn)in•tron(ˈɪn trɒn)n.
intronIntronIn split genes, a portion that is included in ribonucleic acid (RNA) transcripts but is removed from within a transcript during RNA processing and is rapidly degraded. Split genes are those in which portions appearing in messenger RNAs (mRNAs) or in structural RNAs, termed exons, are not contiguous in a gene but are separated by lengths of deoxyribonucleic acid (DNA) encoding parts of transcripts that do not survive the maturation of RNA (introns). Most genes in eukaryotes, and a few in prokaryotes, are split. These include not just a large number of different protein-coding genes but also genes encoding transfer RNAs (tRNAs) in such diverse eukaryotes as yeast and frogs, and genes encoding structural RNAs of ribosomes in some protozoa. Introns are also found in mitochondrial genes of lower eukaryotes and in some chloroplast genes. See Exon The number of introns in a gene varies greatly, from 1 in the case of structural RNA genes to more than 50 in collagen. The lengths, locations, and compositions of introns also vary greatly among genes. However, in general, sizes and locations—but not DNA sequence—are comparable in homologous genes in different organisms. The implication is that introns became established in genes early in the evolution of eukaryotes, and while their nucleotide sequence is not very important, their existence, positions, and sizes are significant. Speculation on the roles and the evolution of introns is mostly based on correlations that have been seen between domains of protein structure and the exons of genes that are defined by intervening introns. For example, the enzyme alcohol dehydrogenase (ADH) has two domains, one portion of the protein that binds alcohol, and another that binds the enzyme cofactor nicotinamide adenine dinucleotide (NAD). The ADH gene has an intron that cleanly separates the nucleotide sequences which encode each domain, and gene-sequence arrangements such as this are not uncommon. It has been suggested that introns became established in the genes of eukaryotes (and to a limited extent in bacteria) because they facilitate a genetic shuffling or rearrangement of portions of genes which encode various units of function, thus creating new genes with new combinations of properties. The introns allow genetic recombination to occur between the coding units rather than within them, thus providing a means of genetic evolution via wholesale reassortments of functional subunits or building blocks, rather than by fortuitous recombinations of actual protein-coding DNA sequences. See Gene, Genetic code, Recombination (genetics) intron[′in‚trän]intronin·tron(in'tron),intron(ĭn′trŏn)in·tron(in'tron)intronA non-coding segment of a DISCONTINUOUS GENE. Introns are lengths of DNA interposed between coding segments (EXONS) in a gene and are transcribed into MESSENGER RNA but are then removed from the transcript and the exons spliced together. Introns do not contain biological information.intronor (‘in’ for intervening) - an intervening nucleotide sequence in an INTERRUPTED split gene. Such sequences are transcribed into primary RNA transcripts, but then excised from the RNA, leaving behind the EXON sequences for the functional gene product. See RNA PROCESSING, RNA SPLICING.intron
Synonyms for intron
|
|||
| 随便看 |
|
英语词典包含2567994条英英释义在线翻译词条，基本涵盖了全部常用单词的英英翻译及用法，是英语学习的有利工具。