ZOOHCC - 501: Molecular Biology (Theory)
Unit 4: Translation
Split genes
Split genes are genes found in eukaryotic organisms that are composed of coding regions called exons, which are separated by non-coding regions called introns. The process of splicing removes the introns from the pre-mRNA, resulting in a mature mRNA that contains only the exons, which are then translated into a protein. Split genes allow for greater flexibility and control in gene expression, and can also result in different mRNA isoforms from a single gene through alternative splicing.
Split genes are genes that consist of coding regions (exons) and non-coding regions (introns). Unlike simple organisms such as bacteria, where genes are usually uninterrupted coding sequences, eukaryotic genes are often split into multiple exons separated by introns.
The process of dividing genes into exons and introns is thought to have evolved in eukaryotes to provide greater flexibility and control of gene expression. Splicing of introns from the pre-mRNA (precursor mRNA) occurs during the transcription process, resulting in a mature mRNA containing only the coding region (exons). The splicing process is carried out by a complex composed of several small nuclear RNAs (snRNAs) and proteins called spliceosomes. Splitting the gene into exons and introns also allows for alternative splicing. In this case, different combinations of exons can be spliced together to generate different mRNA isoforms from a single gene. This increases the diversity of proteins that can be produced from a single gene and enables tissue-specific expression patterns.
The discovery of split genes and the mechanisms of intron splicing was a major breakthrough in molecular biology and awarded the 1993 Nobel Prize in Physiology or Medicine to Richard J. Roberts and Philip A. Sharp.
Concept of introns and exons
Introns and exons are two types of regions that are found within genes, particularly in eukaryotic organisms.
Exons are the regions of DNA that contain the genetic information that is used to code for a protein. Exons are transcribed into messenger RNA (mRNA), which carries the genetic information from the nucleus to the ribosomes in the cytoplasm, where it is translated into a protein.
Introns, on the other hand, are regions of DNA that do not code for protein. During transcription, the introns are transcribed into mRNA along with the exons, but then they are removed by a process called splicing, leaving only the exons in the mature mRNA.
The process of splicing is carried out by a complex of RNA and proteins called the spliceosome. The spliceosome recognizes the junction between the exon and the intron, cuts the RNA at these points, and then splices the exons together to form the mature mRNA.
The presence of introns allows for alternative splicing, where different combinations of exons can be joined together to produce different mRNA isoforms from the same gene. This process contributes to the diversity of proteins that can be produced by a single gene.
In summary, exons contain the genetic information that codes for a protein, while introns do not. Both exons and introns are transcribed into mRNA, but only the exons are spliced together to produce the mature mRNA that is translated into protein. The presence of introns allows for alternative splicing and contributes to the diversity of proteins that can be produced from a single gene.
Difference between Intron and exon
- Introns and exons are two distinct types of regions that are found within genes, particularly in eukaryotic organisms. Here are the main differences between introns and exons:
- Definition: Exons are the coding regions of DNA that contain the genetic information used to code for a protein, while introns are non-coding regions of DNA that do not contain any protein-coding information.
- Function: Exons contain the information that is used to produce a functional protein, while introns do not play a direct role in protein production.
- Splicing: During transcription, both exons and introns are transcribed into pre-mRNA. However, during RNA processing, introns are removed from the pre-mRNA through a process called splicing, leaving only the exons. Exons are then spliced together to produce the mature mRNA that is translated into protein.
- Size: Exons are generally shorter in length compared to introns, which can be quite long.
- Number: Genes can have multiple exons and introns, and the number of exons and introns can vary greatly between genes.
- Alternative splicing: The presence of introns allows for alternative splicing, which enables the production of multiple mRNA isoforms from a single gene by different combinations of exon splicing.
- Evolution: Intron-exon structures are common in eukaryotes, while prokaryotic genes generally do not have introns. The presence of introns is thought to have evolved in eukaryotes to allow for more complex regulation of gene expression and the production of multiple protein variants from a single gene.
In summary, exons are coding regions of DNA that contain the genetic information used to code for a protein, while introns are non-coding regions of DNA that do not contain any protein-coding information. During RNA processing, introns are removed, leaving only the exons, which are spliced together to produce the mature mRNA. The presence of introns allows for alternative splicing, which enables the production of multiple mRNA isoforms from a single gene.
