Chemistry Is the Foundation of Life, But What Does It Mean to Be Alive?

ChemMatters
Illustration of DNA structure
Credit: DepositPhotos

by Max G. Levy


It may seem easy to distinguish whether something is alive or not. You are alive, as is your teacher, and the trees you see on your way to school. Your desk and chair are not alive, and neither are the cars, buses, bikes, and shoes that brought you to class. But why? You learn in biology that living things are made of cells. Every person, animal, plant, microbe, and fungus passes this test, while all of that other stuff doesn’t. 

Here is a handy rubric: Cells metabolize chemicals, they produce and consume energy, and they replicate and respond to stimuli. But a rubric is not a definition, and as we examine this frontline between biology and chemistry, this seemingly rigid boundary between alive and not alive begins to look porous.

Vitalism or Emergence

For centuries, many scientists believed that all life shares a “vital force” that the principles of chemistry and physics cannot explain. Proponents of this so-called vitalism argued that living creatures produce organic compounds otherwise impossible to create outside of a biological environment. Thus, biology was distinctly beyond the reach of true scientific understanding. 

Today, however, biologists, chemists, and physicists don’t believe in vitalism. We understand that the processes associated with the rubric of life can in fact be explained by chemistry and physics. Cells copy their DNA, catalyze chemical reactions, and replicate, thanks to complex biomolecules refi ned over billions of years of evolution. And, complex or not, these biomolecules are still just molecules—chemical compounds that interact predictably with their environment.

By most accepted conventions, a biomolecule is not alive. Even viruses don’t make the cut. Viruses contain a mixture of genetic material, proteins, and (sometimes) lipid shells. Viruses may use these simple components to invade cells and hijack the machinery necessary to copy themselves, but they are not traditionally considered to be alive. Viruses can’t self-replicate independent of a host; self-replication is a defining feature of cells.

Cells are alive because they can metabolize chemicals, replicate, respond to stimuli, and maintain a chemical homeostasis. We are alive because we are made of these cells and because we can do these “life rubric” functions on a larger scale as well. 

This suggests that our notion of “life” is not so concrete. If your heart suddenly stops, you may no longer be alive, but your cells can continue to function. As the cells eventually falter, enzymes and organelles within them can continue their life-giving functions. 

Life emerges from this basic chemistry. But where life stops and starts remains an open question.

...living organisms would cease to exist without the nonliving world around them, and the nonliving world is constantly shaped by living organisms....

Origins of Life—Small and Vast

Some scientists hypothesize that all complex life on Earth originated from ribonucleic acids, or RNA. RNA can catalyze chemical reactions, and its molecules contain sequences of nucleotides. These traits may have primordial RNA with chemical functions that eventually gave rise to cells: storing information, interacting with nearby molecules, and self-replication.

Newer movements in science argue that Earth is alive in a broader sense. This idea is related to the Gaia Hypothesis codeveloped by chemist James Lovelock about 50 years ago. The Gaia hypothesis states that organisms interact synergistically with their inorganic surroundings. It’s all about self-regulation. In other words, because living organisms would cease to exist without the “nonliving” world around them, and the nonliving world is constantly shaped by living organisms, one can wonder whether our definition of living versus nonliving is useful at all. 

As author Ferris Jabr writes in his book Becoming Earth: “For the first half-billion years of its existence, the planet was a purely geological construct. As the first living creatures adapted to the planet’s primordial features and rhythms, they began to play upon them, too, each changing the other. Since then, biology and geology, the animate and inanimate, have been locked in a perpetual and increasingly elaborate duet.” Earth’s atmosphere, carbon cycle, oceans, climate, and geology have all changed under the influence of its creatures. Put simply: The conditions for life on Earth are held in equilibrium by life on Earth. What this means is that geoscience is an inextricable component of biology. 

Why might it be important to discuss what is alive, whether that means adopting a narrow defi nition or a broad one? Chemistry doesn’t answer these questions for us, but it gives us a language to debate the issue. So, what does “life” mean to you? It’s Open for Discussion.

Max G. Levy has a Ph.D. in chemical and biological engineering and is a freelance science journalist based in Los Angeles, California.


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