Difference Between Exome and Transcriptome

The main difference between exome and transcriptome is that the exome is the complete sequence of all exons in protein-coding genes in the genome whereas the transcriptome is the collection of messenger RNA molecules derived from protein-coding genes. Furthermore, exome covers 1-2% of the total genome sequence while transcriptome makes up less than 4% of the total RNA of the cell. 

Exome and transcriptome are two collections of sequences in protein-coding genes in the genome. Both have various applications in genomic studies as well as in disease diagnosis. 

Key Areas Covered 

1. What is Exome
     – Definition, Facts, Techniques
2. What is Transcriptome
     – Definition, Facts, Techniques
3. What are the Similarities Between Exome and Transcriptome
     – Outline of Common Features
4. What is the Difference Between Exome and Transcriptome
     – Comparison of Key Differences

Key Terms 

Exon, Exome, mRNA, Protein-Coding Genes, Transcriptome

What is Exome 

The exome is the collection of exons in the protein-coding genes of the genome of a particular organism. The coding sequence of the genome is clustered into genes, which can be either coded for proteins or RNA. In the prokaryotic genome, the coding sequence is not interrupted by other sequences while in the eukaryotic genome, the coding sequence of the gene is interrupted by non-coding sequences called introns. Hence, the clustered coding sequences are called exons.

Figure 1: Exons and Introns

In protein-coding genes, RNA polymerase transcribes introns as well as exons into the precursor mRNA during transcription. The incorporated introns are removed during the following post-transcriptional modifications. The main technology used in the study of the exome is the whole-exome sequencing (WES). WES is involved in the hybridization of the fragmented DNA of a particular genome in order to identify the target DNA sequences followed by sequencing. 

What is Transcriptome 

Transcriptome is the total set of mRNAs expressed in a cell. It accounts for less than 4% of the total RNA of the cell. Since transcriptome specifies the composition of the proteome, it determines the biochemical capacity of that particular cell. Also, transcriptome of a particular cell cannot be synthesized and it always comes to the daughter cell from the parent cell during cell division. Thus, transcription, which is the process of producing RNA is the step for the maintenance of the transcriptome.

Figure 2: Transcriptome of Pluripotent Cell

On the other hand, though each cell contains information for the production of the entire transcriptome of the species, the expressing genes in the cell depends on the environmental factors as well. The two main technologies used in the study of transcriptomes are microarray and RNA-seq. 

Similarities Between Exome and Transcriptome 

• Exome and transcriptome are two sets of nucleotide sequences found in the genome. 
• Both are associated with the information in the protein-coding genes. 
• They are made up of exons. 

Difference Between Exome and Transcriptome 

Definition 

Exome refers to the part of the genome consisting of exons, which code information for protein synthesis while transcriptome refers to the sum total of all the messenger RNA molecules expressed in the genes of an organism. The main difference between exome and transcriptome is thus self explanatory from this definition.

Significance 

Hence, the exome is the total set of exons in the protein-coding genes while the transcriptome is the total set of mRNAs expressed in the cell. 

DNA or RNA 

Also, the exome is made up of DNA while transcriptome is made up of RNA. 

Amount 

Exome represents 1-2% of the total genome while transcriptome represents less than 4% of the total RNA of the cell.

Level 

Another difference between exome and transcriptome is that the exome is in the genomic level while the transcriptome is in the transcription level. 

Techniques 

Furthermore, whole-exome sequencing is the technique to determine the exome while microarray and RNA-seq determine the transcriptome. 

Conclusion 

The exome is the entire set of exons in the genome determined by the WES of the genome. Hence, exome is a DNA-based concept. But, transcriptome is an RNA-based concept since it is the entire set of mRNAs of the cell. The main difference between exome and transcriptome is their concept. 

Reference:

1. Warr, Amanda et al. “Exome Sequencing: Current and Future Perspectives.” G3: Genes|Genomes|Genetics 5.8 (2015): 1543–1550. PMC. Web. 6 Sept. 2018. Available Here
2. Brown TA. Genomes. 2nd edition. Oxford: Wiley-Liss; 2002. Chapter 3, Transcriptomes and Proteomes. Available Here

Image Courtesy:

1. “DNA exons introns” By National Human Genome Research Institute –  (Public Domain) via Commons Wikimedia  
2. “The transcriptome of pluripotent cells” By Grskovic, M. and Ramalho-Santos, M., The pluripotent transcriptome (October 10, 2008), StemBook, ed. The Stem Cell Research Community, StemBook, doi/10.3824/stembook.1.24.1, http://www.stembook.org. – [1] DirectStemBook Figure 2 The transcriptome of pluripotent cells.Grskovic, M. and Ramalho-Santos, M., The pluripotent transcriptome (October 10, 2008), StemBook, ed. The Stem Cell Research Community, StemBook, doi/10.3824/stembook.1.24.1, http://www.stembook.org. (CC BY 3.0) via Commons Wikimedia