While the genome may be the blueprint for an organism, proteins are the structural and functional molecules required by virtually all life processes. Therefore, to truly understand how an organism functions, we need to understand more than just its genome – we need to understand the proteome and all the other 'omes' as well. For this reason, proteomics is one of the fastest-growing areas of biological research now that the human genome has been mapped. However, unveiling the proteome is not a simple task.

If sequencing the human genome was a massive undertaking, consider some of the challenges involved in creating a map of the human proteome:

• Firstly, there are far more proteins in an organism than there are genes.
  
  Part of the reason for this is that messenger RNA (mRNA), the mobile copy of DNA which is used as a template when a cell creates a protein, can undergo 'editing' after it is first copied. Segments of the RNA can be removed before a protein is created from it, meaning a number of different proteins can be created from the same gene. Even after the protein has been translated from the mRNA it can still undergo numerous transformations including the addition of chemical groups, the removal of sections of the protein, and combination with other proteins – any of which can alter the form and function of the finished molecule. An extreme example is a fruit fly gene which was discovered by scientists to code for 38,000 different proteins! So while we now know that humans have approximately 30,000 genes, our total number of proteins is still unknown – although estimates put the total at 100,000 or more.

• Secondly, while the genome remains relatively static in any given cell in an organism, the expression of the proteome changes from cell to cell and from moment to moment. Age, gender, health, and recent consumption of food or drugs all affect the proteome – the same cell, if examined at different times or under different conditions, can be expressing a different complement of proteins.

• Thirdly, cells from different tissues within the same organism express distinct sets of proteins.

These and other factors involved in making a map of the human proteome present a challenge worthy of the potential rewards it might offer.¹⁷