From Molecules to Metabolism — III. When Chemistry Needed an Inside

A cycle can sustain itself.

But it cannot sustain itself from nothing.

Matter must enter.

Energy must enter.

Waste must leave.

So the chemical network must somehow regulate its relation to what surrounds it.

This creates a curious problem.

To have an organised inside, there must first be some difference between inside and outside.

But perhaps that difference does not need to appear all at once.

A chemical network can alter its local environment. Products accumulate. Gradients form. Surfaces concentrate molecules. Some reactions become more likely in one location than another.

Organisation begins to acquire a place.

And once processes become locally concentrated, the distinction between what belongs to the network and what does not becomes increasingly consequential.

The chemistry has begun to need an inside.

This does not mean that a membrane suddenly appears around an already completed organism.

It suggests something subtler.

Boundary and metabolism may have emerged together.

A boundary makes a chemical network more stable by controlling exchange. But the network can also contribute to maintaining or modifying the boundary. The two become mutually dependent.

Now something genuinely new is possible.

The system can preserve differences between itself and its surroundings while remaining open to them.

It can take in some things and exclude others.

It can retain useful products and release others.

It can maintain gradients rather than simply dissipating them.

The inside is no longer merely a location.

It has become a condition of organisation.

And this changes the meaning of the chemistry within it.

A molecule inside the system participates in a network of relations that would not exist in the same way outside it. The same reaction can have different consequences depending on where it occurs and what other processes surround it.

Chemistry has acquired context.

The network is beginning to constitute a world of its own.

But that world remains dependent on the larger world around it.

This is the strange architecture of life:

separation makes exchange possible.

A completely closed system would eventually run down.

A completely open system could not maintain its organisation.

Life occupies the relation between the two.

Perhaps the transition from chemistry to metabolism therefore requires more than reactions that sustain one another.

It requires a system capable of organising its own difference from its surroundings.

And once chemistry has an inside, we can ask the next question:

What happens when the chemistry inside begins to maintain the boundary that makes the inside possible?