The Vital Question

My review of Nick Lane's book The Vital Question in The Times:

Nick Lane is not just a writer of words about science, he is
also a doer of experiments and a thinker of thoughts. And these
days he is hot on the trail of one of the biggest ideas in the
universe: the meaning of the word “life”. In this, his third book
about energy and life, he comes triumphantly close to cracking the
secret of why life is the way it is, to a depth that would boggle
any ancient philosopher’s mind. He can now tell a story of how,
when and where life started, and what happened to it in its early
days. Most of that story looks as if it is true.

Life uses information (stored in DNA) to capture energy (which
it stores in a chemical called ATP) to create order. Humans burn
prodigious amounts of energy — we generate about 10,000 times as
much energy per gram as the sun. The sun is hotter only because it
is much bigger. We use energy to create and maintain intricate
cellular and bodily complexity, the opposite of entropy, just as we
do in the economy, where the harnessing of power from burning fuel
enables us to build skyscrapers and aeroplanes. But we — and here
“we” means all living creatures, including bacteria — have an
idiosyncratic way of trapping energy to make it useful. We pump
protons across lipid membranes.

During every second of your life you pump a billion trillion
protons across membranes in the thousand trillion mitochondria that
live inside your body. Mitochondria are the topic of recent
parliamentary debates (about “three-parent embryos”), the central
characters in this book and the descendants of bacteria. Their job
is to oxidise carbon and hydrogen so as to pump protons and fuel
life.

The collapse of these proton gradients is the true definition of
death. Cyanide is a poison because it blocks the proton pump, and
cells commit suicide (to rid the body of bad mutations) by
deliberately collapsing their proton gradients. A freshly dead body
is, to all intents and purposes, identical to a living one, except
that on a minuscule, invisible scale, its ability to keep protons
the right side of membranes has suddenly ceased.

Professor Lane, a biochemist at University College London, and
his colleagues have worked out why this is and what it means. His
exploration of the story takes him deep into conundrums that have
fascinated human beings for millennia: species, death, sex, gender,
ageing, fertility and health. In 2000 a new kind of alkaline,
warm-water vent was found on the ocean floor in the mid-Atlantic
(it was dubbed the Lost City because of its huge carbonate chimneys
and towers), where protons diffuse across thin, semi-conducting
walls of iron, nickel and sulphur into minuscule pores, causing
organic molecules to accumulate and interact.

This, Lane and others now think, was how life got started some 4
billion years ago, inside these rocky pores, where the natural
proton gradients came by accident to drive the generation of
molecular complexity. The details of the detective story that gets
him from this point to the first bacterium-like cell are
challenging (to understand), intricate and compelling, but well
worth the journey.

Life seems to have diverged very early on into two different
kinds with different chemistry sets. We call them bacteria and
“archaea”, but they both look like microbes. It was only when we
read their genes that we realised how different they were — one
uses right-handed forms of lipids, the other left-handed, for
instance. For a staggering two billion years they were all there
was on this planet. They both had great biochemical diversity but
small size and structural simplicity.

Only after this time did large cells and complex creatures
emerge — protozoa, plants, animals, fungi. These things have huge
internal complexity in their cells as well as bodies that are often
multicellular. They all share a single common ancestor because
their basic machinery is always the same: plants and animals are
mere variations on a theme. And yet this lurch to complexity has
left little trace — there are no surviving intermediate creatures
with bits of the machinery, but not other bits. How could complex
(“eukaryotic”) life have sprung fully formed, like Athena from the
head of Zeus?

Solving this mystery leads Lane into a world of ideas that only
Lewis Carroll could make sense of. Six impossible things become
believable before breakfast when you are reading a Lane book, and
there are plenty here.

What seems to have happened is that a single archaeal cell
engulfed a single bacterial cell that turned into a specialised
energy generator and gradually passed most of its genes to the
host.

This caused a problem because it brought rogue DNA sequences, or
digital parasites — a bit like computer viruses — into the
operating system of the host. We are still plagued by them today.
They are called introns, and we deal with them by splicing them out
of the transcript of DNA before using it. The machine we use to do
this works slowly so it has to have a safe place to work before the
transcripts get used — and that is why the nucleus evolved, to
separate transcription from translation (into protein).

Having mitochondria, as the bacteria became, enabled cells to
grow much larger, because the mitochondria could be numerous and
small and shrink their genomes to just the essential genes — we
have just 13 in ours — while the archeal genome could start to
service a much larger volume and generate new kinds of
machinery.

Lane’s crucial insight, his eureka moment, was when he realised
that, thanks to this division of labour, the energy available per
gene is hundreds of thousands of times greater in a eukaryotic cell
than in a bacterium: just as the energy available per worker leapt
higher in the Industrial Revolution enabling the construction of
much more technology and infrastructure (my analogy, not his).

From here Lane traces the echoes of ancient struggles inside the
cell, shedding light on questions such as why we have less sodium
in our cells than seawater has, why pigeons live longer than rats,
how species come to separate, why eggs are large and sperm small,
and so on.

The material Lane has to work with is almost impossibly
complicated and there are times when even the most dedicated reader
will have to keep turning to the glossary to check the meaning of
terms. But like the best science writers, Lane never glosses over
the detail. Instead he turns it into a series of detective stories.
Poirot-like he leads you from the crime to the perpetrator, from
the puzzle to the solution. The difference from a detective story
is that these tales are real, and fundamental to life itself.