Introns

Definition

Introns are non-coding sequences of DNA that are found within genes and are transcribed into RNA but are removed during the RNA processing before translation. Their presence in eukaryotic genes contributes to the complexity of gene expression and regulation, as well as mRNA maturation. In contrast, prokaryotic genes generally lack introns, leading to differences in transcription processes between these two domains of life.

5 Must Know Facts For Your Next Test

1. Introns can vary greatly in size and number among different genes and organisms, with some genes containing many introns while others have none.
2. In eukaryotes, the transcription process creates pre-mRNA, which includes both introns and exons before undergoing splicing to produce mature mRNA.
3. Introns may play a role in gene regulation, as they can contain regulatory elements that influence gene expression levels.
4. The existence of introns allows for alternative splicing, which increases protein diversity without needing to encode additional genes.
5. In prokaryotes, the lack of introns simplifies gene organization and enables immediate translation of mRNA without the need for splicing.

Review Questions

• How do introns affect the process of transcription and subsequent mRNA processing in eukaryotic cells?
  • Introns affect transcription by being transcribed along with exons into pre-mRNA. Once this pre-mRNA is synthesized, splicing occurs to remove introns and join exons, resulting in mature mRNA ready for translation. This added step in eukaryotic cells contrasts with prokaryotes, where mRNA is often immediately translated as it is synthesized because they lack introns.
• Discuss the significance of alternative splicing in relation to introns and how it contributes to protein diversity.
  • Alternative splicing is significant because it allows a single gene to produce multiple protein isoforms by varying which exons are included in the final mRNA. Introns play a crucial role in this process by providing the necessary sequences that can be included or excluded during splicing. This flexibility in splicing not only enhances protein diversity but also enables organisms to adapt more efficiently to varying cellular demands and environmental conditions.
• Evaluate the evolutionary implications of intron presence in eukaryotic genes compared to prokaryotic genes.
  • The presence of introns in eukaryotic genes suggests an evolutionary advantage related to genetic complexity and adaptability. Introns may facilitate regulatory mechanisms that enhance gene expression control and contribute to the evolutionary innovation through alternative splicing. In contrast, prokaryotic genes typically lack introns, resulting in more straightforward transcription and translation processes. This difference implies that eukaryotes have evolved more complex gene structures that allow for greater versatility in their biological functions compared to prokaryotes.

Related terms

Exons: Exons are the coding sequences of a gene that remain in the final mRNA after introns are spliced out, ultimately coding for proteins.

Splicing: Splicing is the process of removing introns from the pre-mRNA transcript and joining exons together to form mature mRNA.

Alternative Splicing: Alternative splicing is a regulatory mechanism by which different combinations of exons are joined together to produce multiple protein variants from a single gene.