Fundamentals of Molecular Biology. Part 2: Molecular Genetic Mechanisms - A. N. Ogurtsov 2011

Genomics and Proteomics
Genome Size

The combination of sequencing techniques and computational Gene-finding algorithms has made it possible to identify all protein-coding genes in numerous organisms. Figure 116 illustrates the total number of protein-coding genes in several fully sequenced Eukaryotic Genomes.

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Figure 116 - Comparison of the total number and specialization of protein-coding genes across various eukaryotic genomes

The Functions of approximately half of the Proteins encoded in these genomes are either already known or have been predicted based on computer-assisted sequence comparisons with homologs. It turns out that genome size does not correlate with our intuitive perception of an Organism's biological complexity.

For instance, the nematode roundworm Caenorhabditis elegans possesses more genes than the fruit fly Drosophila melanogaster, even though the latter has a much more complex Organization and significantly more diverse behavior than the worm.

Even more unexpected is the fact that The Human Genome is only about twice the size of the nematode genome, despite the colossal difference in their anatomy and physiological functions.

Clearly, a simple "arithmetic" difference in gene count cannot serve as a criterion for the biological complexity of organisms. However, certain biological processes can significantly diversify the "repertoire" of expressed proteins in higher eukaryotes.

1. First, this is The phenomenon of alternative pre-mRNA splicing, which makes it possible to generate various functional mRNA copies from a single gene.

2. Second, various post-translational modifications of proteins lead to The Emergence of functional diversity among them.

3. And finally, in different organisms, functional variations can be explained by qualitative differences in Protein-Structure/156.html">Protein Interactions, their diverse associations, and differences in their integration into Various metabolic pathways.

To this day, the specific functions of many genes and proteins predicted by genomic sequence comparisons remain unidentified. As researchers investigate a growing number of specific proteins across an increasing number of organisms and unravel the details of their interactions, our understanding of the complexity and multifaceted Nature of the genetic foundations underlying complex biological systems will continue to grow.