US researchers say they have created a "virtual" model of all the biochemical reactions that occur in human cells.
Scientists can use the virtual model instead of working on real cells
They hope the computer model will allow scientists to tinker with metabolic processes to find new treatments for conditions such as high cholesterol.
It could also be used to individually tailor diet for weight control, the University of California team claimed.
Their development is reported in the journal, Proceedings of the National Academy of Sciences.
A team of six bioengineering researchers at the University of California analysed the human genome to see what genes corresponded to metabolic processes, such as those responsible for the production of enzymes.
They spent a year manually going through 1,500 books, review papers and scientific reports from the past 50 years before constructing a database of 3,300 metabolic reactions.
The information was then used to create a network of metabolic processes in the cell, similar to a traffic network.
Study leader Professor Bernhard Palsson said the network could be used to see what would happen if a drug was used to target a specific metabolic reaction, such as the synthesis of cholesterol.
Or it could be used to predict what would happen if you interfere with a metabolic reaction in a specific type of cell, such as a blood or heart cell.
And eventually it could even be used to create an individual network for a person.
"The new tool we've created allows scientists to tinker with a virtual metabolic system in ways that were, until now, impossible, and to test the modelling predictions in real cells," said Mr Palsson, who is professor of bioengineering and medicine.
"You can take a drug target and you can make the flow through that reaction more and more restrictive or you can calculate all the reactions that you have to go through to make a certain product."
Metabolic reactions in cells include those which convert food sources, such as fats, protein and carbohydrate into energy and to make other molecules used by the body.
There are hundreds of human disorders which are a result of problems with metabolism.
One example is haemolytic anaemia, a condition where red blood cells are broken down too rapidly.
To test the computer model, the team ran 288 different simulations, such as the synthesis of hormones, testosterone and oestrogen, and the metabolism of fat from the diet.
"We all have natural variation in the capacity of these pathways, for example in our ability to make cholesterol, so you could make a metabolic model for an individual person which is a tantalising prospect."
Keith Frayn, professor of human metabolism at the University of Oxford, said the model would allow scientists to spot potential problems with targeting certain reactions early on in their research.
"It's increasingly recognised there are these networks of metabolism and we need to know if we target something how that will spread out and this is potentially a way of dealing with that."
Dr Anthony Wierzbicki, consultant in specialist laboratory medicine at St Thomas's hospital, has done a lot of work on the role of cholesterol in heart disease.
"This is a potentially interesting tool for investigating metabolism of which cholesterol biochemistry forms a part," he said.
But he added that the model would have to be "sophisticated" enough to predict what happens in the production and breakdown of cholesterol as well how it is absorbed from the gut as the two were closely linked.