Exons

Definition

Exons are the coding sequences within a gene that are retained in the mature messenger RNA (mRNA) molecule and ultimately translated into the amino acid sequence of a protein. They represent the functional, protein-coding regions of a gene, in contrast to the non-coding introns that are removed during the process of RNA splicing.

5 Must Know Facts For Your Next Test

1. Exons contain the protein-coding sequences that are ultimately translated into the amino acid sequence of a protein.
2. The number and arrangement of exons within a gene can vary, and this diversity contributes to the complexity of gene expression and the potential for alternative splicing.
3. Exons are separated by non-coding sequences called introns, which are removed during the process of RNA splicing.
4. The 5' and 3' untranslated regions (UTRs) of the mRNA, which flank the coding exons, also play important roles in regulating gene expression and translation.
5. Mutations or variations within exons can have significant impacts on the structure and function of the resulting protein, potentially leading to genetic disorders or diseases.

Review Questions

• Explain the role of exons in the process of gene expression and protein synthesis.
  • Exons are the coding sequences within a gene that are retained in the mature mRNA molecule and ultimately translated into the amino acid sequence of a protein. During transcription, the genetic information from DNA is copied into a pre-mRNA molecule, which then undergoes RNA splicing to remove the non-coding introns and join the remaining exons. This processed mRNA is then transported to the ribosomes, where the exon-derived coding sequences are translated into a polypeptide chain, which folds and assembles into the final functional protein.
• Describe how the diversity of exon arrangement within a gene contributes to the complexity of gene expression and protein diversity.
  • The number and arrangement of exons within a gene can vary, and this diversity is a key contributor to the complexity of gene expression and the potential for alternative splicing. During RNA splicing, different combinations of exons can be retained or excluded from the final mRNA, leading to the production of multiple protein isoforms from a single gene. This allows for a single gene to encode several related, but distinct, proteins with potentially different structures and functions. This diversity in protein products is essential for the versatility and adaptability of living organisms, as it enables a single gene to fulfill multiple biological roles.
• Analyze the potential impact of mutations or variations within exons on the structure and function of the resulting protein, and discuss the implications for genetic disorders and diseases.
  • Mutations or variations within exons can have significant impacts on the structure and function of the resulting protein. Since exons contain the protein-coding sequences, changes in the DNA sequence of exons can lead to alterations in the amino acid sequence of the polypeptide chain. These changes can disrupt the proper folding, stability, or activity of the protein, potentially resulting in genetic disorders or diseases. For example, a single nucleotide substitution within an exon may cause a change in a critical amino acid, leading to the production of a dysfunctional protein that can no longer perform its intended biological role. Understanding the relationship between exon variations and their effects on protein structure and function is crucial for identifying the genetic basis of many inherited and acquired diseases, as well as developing targeted therapies to address these genetic defects.

Related terms

Introns: Introns are the non-coding sequences within a gene that are removed from the pre-mRNA during the process of RNA splicing. They do not contribute directly to the final protein sequence.

RNA Splicing: RNA splicing is the process of removing introns and joining the remaining exons to create a mature, functional mRNA molecule that can be translated into a protein.

Transcription:

Transcription is the process of copying the genetic information from DNA into a single-stranded RNA molecule, which then undergoes further processing to become a mature mRNA.