Exon

Definition

An exon is a segment of DNA or RNA that codes for a portion of a protein. These sequences are important as they are expressed, or 'spliced' together during the process of transcription and translation to form mature messenger RNA (mRNA). Exons are interspersed with non-coding regions called introns, which are removed during RNA processing, highlighting their critical role in the overall flow of genetic information from DNA to functional proteins.

5 Must Know Facts For Your Next Test

1. Exons can vary in size and number within different genes, contributing to the diversity of proteins produced in an organism.
2. The process of splicing exons together is crucial for generating functional mRNA, which then directs protein synthesis in ribosomes.
3. Mutations in exon sequences can lead to diseases or abnormal protein functions, making their integrity vital for proper cellular functions.
4. In eukaryotic organisms, exons represent only a fraction of the total gene length due to the presence of introns.
5. Alternative splicing allows for different combinations of exons, enabling organisms to produce various protein isoforms from a single gene.

Review Questions

• How do exons and introns contribute to the complexity of gene expression in eukaryotes?
  • Exons and introns work together to regulate gene expression by allowing for alternative splicing. While exons are the coding sequences that will be expressed as proteins, introns are non-coding regions that need to be removed from the precursor mRNA. This unique arrangement enables eukaryotic cells to produce multiple protein variants from a single gene through alternative splicing, significantly increasing protein diversity and adaptability.
• Discuss the implications of mutations occurring in exon sequences compared to those occurring in intron sequences.
  • Mutations in exons have more direct implications for protein function because they can alter the amino acid sequence encoded by the corresponding mRNA, potentially leading to dysfunctional proteins. In contrast, mutations in intron sequences may not always affect protein coding since these regions are removed during RNA processing. However, if an intron mutation affects splice site recognition, it could disrupt normal exon splicing patterns and lead to abnormal protein production or disease.
• Evaluate the role of alternative splicing involving exons in generating proteomic diversity and its significance in cellular function.
  • Alternative splicing plays a pivotal role in generating proteomic diversity by allowing different combinations of exons to be included in mRNA transcripts. This process enables a single gene to produce multiple protein isoforms with potentially distinct functions, which is crucial for cellular specialization and adaptability. The significance lies in its impact on various biological processes such as development, differentiation, and response to environmental changes, underscoring how variations at the level of exons can lead to complex and dynamic cellular functions.

Related terms

Introns: Non-coding regions of a gene that are transcribed into precursor mRNA but are removed during RNA splicing.

Alternative splicing: A process that allows a single gene to code for multiple proteins by rearranging exons in different combinations during mRNA processing.

Codon: A sequence of three nucleotides in mRNA that corresponds to a specific amino acid or stop signal during protein synthesis.