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Scientists exploring the obscure world of human proteins have uncovered a large number no-one knew existed.

Regions of DNA not previously thought to code for proteins produced 193 of the novel molecules, whose functions remain a mystery.

The findings suggest that the human genome, or genetic code, is much more complex than had been assumed.

The findings suggest that the human genome, or genetic code, is much more complex than had been assumed. The researchers say 'You can think of the human body as a huge library where each protein is a book.'

The early first draft of the 'proteome', the complete protein catalogue, includes proteins encoded by 17,294 genes - 84% of all the known genes in the body.

Proteins are complex organic molecules responsible for the vast array of life processes.

They act as building blocks of living tissue, drivers of countless chemical reactions, and a fuel source.

Genes are stretches of DNA containing sequences of chemicals that provide the coded "instructions" for protein-making cell machinery.

While science has made a great deal of headway unravelling the secrets of DNA, it has only scratched the surface of proteins.

Professor Akhilesh Pandey, from Johns Hopkins University in the US, who led the new research reported in the journal Nature, said: 'You can think of the human body as a huge library where each protein is a book.

The early first draft of the 'proteome', the complete protein catalogue, includes proteins encoded by 17,294 genes - 84% of all the known genes in the body.

'The difficulty is that we don't have a comprehensive catalogue that gives us the titles of the available books and where to find them.

'We think we now have a good first draft of that comprehensive catalogue.'

The research team began by taking samples of 30 tissues, extracting their proteins, and using enzymes as 'chemical scissors' to cut them into smaller pieces.

The fragments, called peptides, were then run through a series of instruments designed to identify them and measure their abundance.

Many proteins were characterised for the first time, including some never predicted to exist.

The most unexpected finding was that 193 of these molecules could be traced to supposedly non-coding regions of DNA.

'This was the most exciting part of this study, finding further complexities in the genome,' said Prof Pandey.

'The fact that 193 of the proteins came from DNA sequences predicted to be non-coding means that we don't fully understand how cells read DNA, because clearly those sequences do code for proteins.'

He thought scientists would never finish cataloguing the proteome because it was so extensive and complex.

But the new work provided a 'solid foundation' other researchers could build on.