Synthetic life, near or far?

In the previous post I detailed some recent advances in the field of synthetic biology, and asserted, without saying why, that I don’t think the goal of creating an artificial living cell is as near as some optimistic researchers believe, such as Craig Venter.

To explain why, I’ll make a comparison between a living cell and one of our most complex artifacts: the computer. A computer consists of the following two main parts:

1. CPU (central processing unit): as its name indicates, it’s the control center and the place where programs are executed. One of its fundamental elements is the machine language, a relatively complex binary code that the circuits of the unit interpret and execute. Every program, in order to run, must be written in machine language.
2. Memory. There are several types: hard disk, which stores the programs and data accessed by the computer, including the operating system, although many of them will never be used; cache memory, faster than the hard disk, which stores those programs and data currently being used, to speed up their process; external memories (such as flash memory), used to transmit data and programs from one computer to another, or to save copies in case of loss of information.

If we establish a parallel between the computer and a living cell, the DNA of the cell plays a role equivalent to that of a computer’s hard drive. Indeed, its main role is to store all the genes and genetic data chains, but it cannot execute programs; to do this, it needs the collaboration of the rest of the cellular machinery.

Similarly, the messenger RNA of a cell plays the role of a cache memory, as it is an intermediary between DNA and the cellular machinery, transferring from one to the other a copy of a single gene.

Finally, the cell contains what we call cellular machinery: ribosomes, which decipher the information contained in RNA and synthesize proteins; along with other corpuscles, such as mitochondria, that perform the complete oxidation of glucose to supply the cell with energy; and chloroplasts, which carry out the chlorophyll function in those cells that can do it. It is clear that the cellular machinery, although decentralized among numerous cellular organelles, is equivalent to the central processing unit of a computer.

Craig Venter

(Note that the previous parallel is a simplification. If the memory of a computer is fully contained in the hard disk, the DNA of the living cell does not contain the entire memory of the cell. In addition to the genetic data, the cell uses others, called epigenetic, which are distributed in the cytoplasm. Therefore, it is not enough to know the genome (the list of nucleotides in the DNA) to be able to reconstruct a living being. Imaginings on the future construction of human beings from their genomes are, therefore, impossible).

Let us now analyze, in the light of this parallel, the advances made by Craig Venter and his team in recent years in the field of synthetic biology:

• Artificial construction of a viral DNA. It is equivalent to copying the information contained in a hard disk to another hard disk.
• Artificial construction of a mycoplasma DNA. The same as the previous case, only the hard disk contains more information.
• Transplant of DNA from a mycoplasma to a cell of a different related species. It is equivalent to replacing the hard disk of a computer with another hard disk coming from a computer that works with the same machine language, but contains a different operating system (for example, Linux rather than Windows). In principle, the computer with the transplanted hard disk should work with the new operating system.
• Transplant to a mycoplasma of a synthetically generated DNA molecule, slightly modified from the DNA of a different related species. It is equivalent to the previous case.

What is missing, before we can speak about living cell synthesis? In the parallel computer case, we’d have to build a new computer from scratch, with a central processing unit designed and made from elementary components (essentially transistor circuits), capable of understanding a coherent machine language. It will be noticed that this objective would be enormously distant, if all we can do is change hard drives, as is currently the case in the field of synthetic biology. In other words: what remains to be done is precisely the most difficult.

As a possible previous step, theoretically easier, we could try to bring a bacterium back to life: to make a dead bacterium function again as a living being. To make its cellular machinery, which has stopped working, work again. It wouldn’t be synthetic life, but it would be an advance in that direction.

Another question is whether it will be possible to do this sometime. There are philosophical reasons that put it in doubt. But that will be discussed in the next post.

The same post in Spanish
Thematic Thread on Synthetic and Artificial Life: Previous Next

Manuel Alfonseca