Posted on 2024年 11月 6日
Introns and exons refer to regions of DNA and RNA that have different roles, especially found in eukaryotic genes. Exons are the parts that contain protein information, and introns are the non-coding regions in between. These regions play important roles in gene structure and function.
Exon
- Definition: An exon is a region of genetic information that encodes a protein and is the portion of RNA that remains when the RNA matures.
- Function: Exons form proteins as amino acid sequences when transcribed into mRNA and subsequently translated by the ribosome. Exons combine to sequence a specific protein and cause that protein to perform a function in the cell.
- Characteristics: Exons are always present in mRNA after introns have been removed because they are directly involved in protein synthesis.
Intron
- Definition: An intron is a non-coding region of a gene that contains no protein information. Introns are located between exons and are removed during mRNA maturation.
- Function: Introns do not directly code for proteins, but they help regulate gene expression and the production of diverse mRNAs. The presence of introns also enables “selective splicing,” in which different proteins are produced from the same gene.
- Characteristics: Introns do not remain in mature mRNAs and are removed in a process called splicing, but are thought to play an important role in gene regulation and evolution.
Splicing and Selective Splicing
- Splicing: The initial RNA (precursor mRNA) that is produced when a gene is transcribed also contains introns. In a process called splicing, introns are removed from the precursor mRNA and exons are joined to form mature mRNA.
- Selective splicing: a mechanism that produces different mRNAs from the same gene. Different combinations of exons are created during splicing to produce a variety of proteins. This allows a single gene to produce multiple proteins with different functions.
Significance of introns and exons
- Evolutionary significance: introns are thought to help genes in the process of adapting to new traits and have evolutionary advantages because they can efficiently produce diverse proteins through selective splicing.
- Regulation of gene expression: introns may contain signals that control gene expression and may also play a role in regulating gene function.
In general, introns dominate the ratio of introns to exons in eukaryotic genes. The specific ratios vary among species, but the following trends are observed:
- For humans: Human genes contain many introns, with introns accounting for about 90% or more of the total sequence, and exons for only 1% to 2%.
- For other eukaryotes: other mammals and plants also tend to have more introns than exons in their genes. For example, even in mouse and yeast, introns are abundant and exons make up a small percentage, about a few percent of the total gene.
Also, exons are usually short, averaging 100-200 bases, whereas introns are much longer by comparison and can be thousands of bases long.
Conclusion
Exons are protein-coding regions and are found in mature mRNAs. Introns, on the other hand, are non-coding regions that do not contain protein information and are removed by splicing, but contribute to the regulation of gene expression and the production of diverse proteins. The presence of introns and exons enables efficient management of genetic information and more diverse and complex biological activities.
- Introns: often account for more than 90% of the gene sequence (in humans).
- Exons: 1% to 2% of the gene sequence.
This ratio results in a structure in which introns make up a large portion of the gene structure and exons are efficiently utilized as protein coding regions.
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