exon

Examples of exon in the following topics:

• RNA Splicing

  • The regions of RNA that code for protein are called exons .
  • Splicing can be regulated so that different mRNAs can contain or lack exons, in a process called alternative splicing.
  • It can also occur if portions on an exon are excluded/included or if there is an inclusion of introns.
  • Exons A, B, and C can be translated together or Exons A, C, and D can be translated.
  • Once the introns are cleaved and removed, the exons are joined together by a phosphodiester bond.

• mRNA Processing

  • This is supported by the fact that separate exons often encode separate protein subunits or domains.
  • The process of removing introns and reconnecting exons is called splicing.
  • Then the spliceosme connects the 3' end of the first exon to the 5' end of the following exon, cleaving the 3' end of the intron in the process.
  • Then the 3' end of the just-released exon is joined to the 5' end of the next exon, cleaving the bond that attaches the 3' end of the intron to its adjacent exon.
  • This both joins the two exons and removes the intron in lariat form.

• Genome Evolution

  • Processes such as mutations, duplications, exon shuffling, transposable elements and pseudogenes have contributed to genomic evolution.
  • Exon shuffling is a mechanism by which new genes are created.
  • This can occur when two or more exons from different genes are combined together or when exons are duplicated.
  • Exon shuffling results in new genes by altering the current intron-exon structure.
  • Exon shuffling may introduce new genes into the genome that can be either selected against and deleted or selectively favored and conserved.

• Isotype Class Switching

  • The intervening DNA between the S-regions is subsequently deleted from the chromosome, removing unwanted μ or δ heavy chain constant region exons and allowing substitution of a γ, α or ε constant region gene segment.
  • The free ends of the DNA are rejoined by a process called non-homologous end joining (NHEJ) to link the variable domain exon to the desired downstream constant domain exon of the antibody-heavy chain.

• Applications of Genetic Engineering

  • Gene targeting is a different technique that uses homologous recombination to change an endogenous gene, and can be used to delete a gene, remove exons, add a gene, or introduce point mutations.

• Gene Families

  • The positions of exons within the coding sequence can be used to infer common ancestry.

• Genetically Engineered Vaccines

  • Gene targeting is a different technique that uses homologous recombination to change an endogenous gene, and can be used to delete a gene, remove exons, add a gene, or introduce point mutations.

• Antibodies: Classes and Affinity Maturation

  • The variable domain exon is rejoined through a process called non-homologous end joining (NHEJ) to the desired constant region (γ, α or ε).

• RNA and Protein Synthesis

  • The informational DNA segments that make up genes are called exons, and the noncoding segments are called introns.
  • Before the mRNA molecule leaves the nucleus, the nonsense bases that make up the introns are cut out, and the informationally useful exons are joined together in a step known as RNA splicing.