Exon

Definition

An exon is a sequence of DNA that codes for a portion of a mature messenger RNA (mRNA) molecule. Exons are the regions of a gene that are ultimately expressed as the final protein product, and they are separated by non-coding regions called introns.

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 the final protein product.
2. The number and arrangement of exons within a gene can vary, and this diversity contributes to the complexity of gene expression and the production of different protein isoforms.
3. During transcription, the entire gene, including both exons and introns, is initially copied into a pre-mRNA molecule.
4. RNA splicing removes the introns and joins the exons together to create the mature, functional mRNA that can be exported from the nucleus and used as a template for protein synthesis.
5. Mutations in exon sequences can lead to changes in the amino acid sequence of the resulting protein, potentially affecting its structure and function.

Review Questions

• Explain the role of exons in the process of transcription and gene expression.
  • Exons are the coding regions of a gene that are transcribed into the initial messenger RNA (mRNA) molecule. During transcription, the entire gene, including both exons and introns, is copied into a pre-mRNA. However, the introns are then removed through the process of RNA splicing, leaving only the exons to form the mature, functional mRNA. This mRNA is then transported out of the nucleus and used as a template for the synthesis of the final protein product. The sequence of the exons directly determines the amino acid sequence of the resulting protein, making them a crucial component of gene expression.
• Describe the relationship between exons and introns, and explain how their arrangement within a gene can contribute to the complexity of protein isoforms.
  • Exons and introns are distinct regions within a gene. Exons contain the protein-coding sequences, while introns are the non-coding regions that are removed during RNA splicing. The arrangement and number of exons within a gene can vary, and this diversity can lead to the production of different protein isoforms. During the RNA splicing process, different combinations of exons can be included or excluded from the final mRNA, resulting in the translation of distinct protein variants from the same gene. This alternative splicing mechanism allows a single gene to encode multiple protein isoforms, which can have different structures and functions, contributing to the complexity of gene expression and protein diversity within the cell.
• Analyze the potential consequences of mutations occurring within exon sequences, and explain how these changes can impact the structure and function of the resulting protein.
  • Mutations in exon sequences can have significant consequences for the structure and function of the resulting protein. Since exons contain the protein-coding regions, any changes to the DNA sequence within these regions can lead to alterations in the amino acid sequence of the final protein product. Depending on the nature and location of the mutation, this can result in changes to the protein's three-dimensional structure, its stability, its interactions with other molecules, or its overall biological activity. For example, a missense mutation that substitutes one amino acid for another can disrupt the protein's folding or interfere with its catalytic activity. In more severe cases, nonsense mutations that introduce a premature stop codon can lead to the production of a truncated, non-functional protein. Understanding the impact of exon mutations is crucial for identifying genetic disorders and developing targeted therapies to address these genetic defects.

Related terms

Intron: Introns are the non-coding regions of a gene that are removed during the process of RNA splicing. Introns are transcribed into the initial RNA molecule but are then excised before the mature mRNA is exported from the nucleus.

Transcription: Transcription is the process of copying the genetic information from DNA into a single-stranded RNA molecule called messenger RNA (mRNA). This mRNA then serves as a template for the synthesis of a specific protein.

RNA Splicing: RNA splicing is the process of removing introns and joining the remaining exons to form the mature, functional mRNA molecule. This process is essential for the proper expression of genes in eukaryotic cells.