Life is interposed between two energy levels of an electronAlbert Gyorgyi
Photo by Mike – https://www.flickr.com/photos/mjfrig/9560558346/
These words of Albert Gyorgyi are so profound that it can provoke an intense curiosity and fertile imagination. Flow of energy defines life and it was present in living organisms even before the birth of genetic molecules. It is the foundation upon which the origin and evolution of life unfolded.
Even though it sounds very simple, distinguishing life from lifeless things is not an easy task. We have simply put an arbitrary line based on how one wants to define life. In reality everything is a mere continuum. Even before the origin of first organism, this planet had always been ‘alive’. She was teeming with energy, motion, birth and death. Our definition of life is confounded by our thought process which tends to place human in the center of everything. We included things and processes that look like us and move like us as life. It was easy for us to include all the animals. We noticed that plants grow and die, and they were also included. Under the microscope our structure and a bacterial cell had a lot of similarities and we called them ‘little animals’. So far no trouble and it is child’s play. Then came the viruses. Clearly they are barely anything more than a bunch of molecules. But it replicates, it dies and it kills. Half-heartedly we decided to place it under non-living thing by blaming its inability to live independently outside its host. Well, in that sense our host is earth and we won’t survive outside her. It is in the semantics. Bluntly put there is only one fundamental criteria. It is a human-centric approach. Things are alive if it looks like us and it is not a living thing if it does not have any resemblances.
This is a video of a swimming pool on a bright Sunday morning. The water in the pool is agitated by the pool pump that is continuously pulling and pushing water into it. This creates chaos inside and on the surface of the water due to pressure differences created by the pool pump. In the midst of this chaotic motion of water and its molecules you can see organized structures forming spontaneously. These circular shadows are cast by the ‘water swirls’ that form spontaneously on the surface. One can see that these structures are stable for a brief moment then they either disintegrate into the chaos of remainder of the water or divide into smaller swirls and eventually disappear. However new swirls continue to form on the surface. The individual swirls are about the size of tennis ball and probably has trillions and trillions of water molecules cooperating in synchrony as if dictated by some ‘molecular consciousness’ to move in an accurate pattern as long as the whole structure is ‘alive’. In terms of coherence they are as fascinating as our body but only simple in terms of the structural complexity. They serve one purpose – The swirl structure is very effective in dissipating the differences in the pressure created by the pool pump. They are more effective than water molecules moving chaotically to achieve equilibrium. This is the definition of dissipative structure described by Nobel laureate, Ilya Prigogine. Disequilibrium of matter or energy produces chaos in the system. It then spontaneously gives birth to organized dissipative structures in the midst of chaos to dissipate the gradient and achieve equilibrium. The formation of structures like hurricane and tornado in the atmosphere due to differences in the pressure(energy) and heat are similar processes working to achieve equilibrium. Life is also an organized dissipative structure that evolved out of chaos. All of life can be seen as one massive dissipative structure that has been alive for four billion years, evolving in complexity yet connected to each other. Birth and death are merely exchange of materials from one form to another within the same structure.
Four billion years ago, before the first living organism was born, the earth was full of energy in different forms. The earth was soaked by light and heat from the sun. She was sitting in between the 5000 Kelvin Sun and 2.3 Kelvin space. The gravitational energy crushed the materials buried underneath and intermittently spewed molten lava on the surface. Heat and pressure in the atmosphere kept the wind energy flowing. Inorganic elements and molecules exchanged electrons and shuffled their bonding patterns thereby disseminating the chemical energy. All these energies gave rise to innumerable dissipative structures before life came to picture.
One such energy flow gave birth to the first recognizable organism on the ocean floor. Of all types of energy, life chose redox energy as its mother and started to build a carbon based structure 4 billion years ago. We all are very familiar with redox energy. It is the energy released by oxidation – reduction reactions. The redox energy is the source for the flame on the candle, the power from the car engine and the magic in the mitochondria. They all are the same. Jumping of electrons from one energy level to another giving rise to heat and energy. The candle and the car engine burns the carbon skeleton in the fuel with the oxygen in an abrupt manner liberating copious amount of heat. The candle makes a flame with that heat. The car engine is structured in such a way that the heat will be transformed into motion. The cellular machinery is structured in such a way that the carbon skeleton does not interact with oxygen abruptly instead it happens in a choreographed fashion. Oxidation of glucose is carried out stepwise making the electrons jump from one level to another in the electron transport chain. This gradual drop of electron energy makes sure that all the energy is not turned into heat like it happens in a candle or car. Some of the energy is carefully captured to recharge the chemical battery called ATP. The rest of the energy is dissipated as heat and that is why our body is warm. Living structures evolved by capturing the energy released when an electron jumps from one energy level to another. The most fascinating discovery of science is that this process of gradually tunneling the electron down its energy staircase in order to capture a portion of its energy as ATP is universally present in all life forms. The molecular nano-machine that plays a cardinal role in this process called ATP synthase is present in all bacterias, plants, worms, animals and humans. Over these years, even though evolution has generated a great variety of structural complexities ranging from fungi to dinosaurs, the power house that is propelling all these phenomena has not seen much of an innovation in 4 billion years.
The first colony of life had no sophistication to capture the sunlight. It rather depended on chemical energy from inorganic elements. Natural evolution of chlorophyll molecule gave electron transport chain the access to sunlight. The photon from the sun excites an electron in the chlorophyll. As this excited electron falls down to the base level, the energy is captured to charge the ATP battery. This gave living structures access to an unlimited amount of solar energy. We get our share of the pie when we eat the plants or animals. Our body lives by using this chemical energy at the rate of 100 Watt. Controlled burning of the glucose inside the mitochondria captures the energy of falling electrons which we then use to move, feel, see, smell, taste and dream. We will be humbled to know that all movements in our body including the blinking of the eyes and beating of the heart, our consciousness and its dreams are all powered by photons that came from the sun, fell on a chlorophyll molecule and excited its electron.
Life is only a few angstrom away from death
A couple of years ago, one of my patient’s son asked me a question that baffled me for a moment but has remained a source of wisdom since then. It was outside of a critical care unit as I was explaining him the critical state of his father’s illness. He asked me very calmly after listening to everything “How close to death is he?” I was taken aback. Never faced with such a direct question. Is it the distance in meter or time in seconds?
When glucose is burnt inside the cell with oxygen, there is a thin line between abruptly releasing all of the energy as heat(like it happens in the car engine) or tunneling the electron step by step to charge the ATP. The molecular machines are constructed in such a way that electron can only jump from one spot on the molecule to another spot. These spots are separated by only few angstrom distance. One angstrom is 0.0000000001 meter. If by some mutation or by improper construction these molecular sites are separated a little farther away then these electrons would leak away and produce deadly radicals instead of ATP. These radicals send signals to cell to commit suicide, a phenomenon called apoptosis. Our design was perfected to such tiniest of details by natural selection. Any deviation will be penalized by death because it interrupts the foundation upon which life was built – Flow of energy.
- The vital question. Energy, evolution and the origin of complex life. Nick Lane. 2015
- Order out of chaos. Man’s new dialogue with nature. Ilya Prigogine. 1984
- Power, sex and suicide. Mitochondria and the meaning of life. Nick Lane. 2005
- Mitochondria are physiologically maintained at close to 50 degree Celsius. Dominique Chretien et al. PLOS biology. Jan 2018