The human genome contains the complete set of genes required to build a functional human being. However, the genome is only a source of information. In order to function, it must be expressed.
The transcription of genes is the first stage of gene expression and is followed by the translation of messenger RNA to produce proteins. The proteome is the complete set of proteins produced by the genome at any one time.
The proteome is much more complex than either the genome or the transcriptome (see Transcriptomics ). This is because each protein can be chemically modified in different ways after synthesis. Many proteins have carbohydrate groups added to them. Others are phosphorylated or acetylated or methylated.
The proteome is also very dynamic. Most of our cells contain the same genome regardless of the cell type, developmental stage or environmental conditions. The proteome, however, varies considerably in these differing circumstances due to different patterns of gene expression and different patterns of protein modification.
Proteomics, the study of the proteome, is important because proteins represent the actual functional molecules in the cell. When mutations occur in the DNA, it is the proteins that are ultimately affected. Drugs, when they have beneficial effects, do so by interacting with proteins. Proteomics therefore covers a number of different aspects of protein function, including the following:
The techniques for proteome analysis are not as straightforward as those used in transcriptomics. However, the advantage of proteomics is that the real functional molecules of the cell are being studied. Strong gene expression, resulting in an abundant mRNA, does not necessarily mean that the corresponding protein is also abundant or indeed active in the cell.