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The genes contained within the chromosomes found in the nucleus of cells serve as the hereditary blueprints for the construction of proteins. Each gene specifies at least one distinct protein with a unique sequence of amino acids that can be predicted from knowledge of the DNA oligonucleotide sequence of the gene. It is the precise order of four possible nucleotide bases (i.e. A,T,C and G) in a gene that is transcribed faithfully into a unique sequence of amino acids in a protein. Proteins are indirectly constructed from DNA information contained in genes via facsimile copies known as messenger RNA (mRNA). These mRNA oligonucleotide intermediates contain the same or similar nucleotides to their DNA counterparts in genes (i.e. A, U, C and G). Protein synthesis factories known as ribosomes translated the gene DNA sequence information in mRNAs to make proteins.

After the expenditure of over US$3 billion and the dedicated efforts of thousands of scientists, the nucleotide sequence of the human genome (approximately 2.9 billion nucleotides long) has been elucidated. This has revealed the existence of about 21,000 or so human genes. Remarkably, these genes account for less than 3% of the entire nucleotides in the human genome. Since 2001, all of this information (equivalent to 50,000 terabytes of data) has been available for scrutiny in the public domain. The genomes of the mouse, rat, dog, pig, frog and hundreds of other life forms (most of which are bacteria or viruses) have been also been sequenced in their entirety. These genomic studies have revealed how closely connected all of the organisms on the Earth are related to each other. Presently, it costs less than US$ 2,000 to sequence an entire genome, and efforts are underway to sequence the complete genomes of hundreds of thousands of people.
The discovery of all of the human genes is akin to amassing all of the pieces in an unassembled jigsaw puzzle with little guidance as to their purpose and proper arrangement. The real challenge is to connect the proteins encoded by these genes to furnish a clear picture of how physiological processes are mediated and regulated. In other words, we have a parts list and we now have to figure out how the parts fit together to create a working cell. This endeavor has been termed "functional genomics", although "functional proteomics" would be more apt phraseology. Recognition of the importance of this post-genomics research is reflected in the billions of dollars that world government agencies, disease-related charities and the pharmaceutical and biotechnology industry have already committed to this enterprise. Without such a commitment, this genetic legacy cannot realize its tremendous potential.

While all of the cells of the human body contain identical genes, they differ markedly in which genes are activated to produce proteins. With gene microarray technology, it has become feasible to monitor the state of activation of genes as reflected by the production of mRNAs from these genes. It is often assumed that specific mRNA levels correlate with protein levels. The investment of over US $ 1 billion annually on gene microarray analyses is based on this belief. However, it is now rapidly becoming apparent that gene microarray data can be extremely misleading about the actual concentration levels of the proteins encoded by specific mRNA. It is necessary to directly measure the levels of proteins in order to understand how they exert their diverse functions in cells, and how their malfunction leads to human disease.