Biology Reference
In-Depth Information
10
The biochemical factory that autonomously
fabricates itself: A systems biological view of the
living cell
Jan-Hendrik S. Hofmeyr
SUMMARY
The essence of life must lie somewhere between molecule and autonomously
living unicellular organism. Modern biology generally views organisms as beads
along the necklace of lineage; it attempts to explain life from an evolutionary
viewpoint, with reproduction (of cells) and replication (of DNA) as defining phe-
nomena. Systems biology, however, studies each bead per se as an autonomous
entity. I suggest that, for systems biology, the defining difference between a
living organism and any nonliving object should be that an organism is a sys-
tem of material components that are organised in such a way that the system
can autonomously and continuously fabricate itself, i.e. it can live longer than
the lifetimes of all its individual components. Systems biology, therefore, goes
beyond the properties of individual biomolecules, taking seriously their organi-
sation into a living whole.
The concept of autonomous self-fabrication of systems is of course not new;
it has a distinguished history. Although Maturana and Varela's concept of
autopoietic systems is perhaps most prominent in this history, I find that for the
purpose of formalisation it is less useful than either Rosen's theory of replica-
tive metabolism-repair systems or Von Neumann's theory of self-reproducing
automata based on the concept of a universal constructor. Rosen in particular
has shown, using category theory, how to describe such organisations in terms
of relational models, although he never realised his metabolism-repair systems
