Friday, August 5, 2011

Temperature and Metabolism Interact to Create Life

One of the most amazing aspects of cell biology is the chemistry that takes place within the cell walls. The cell takes full advantage of the laws of physics and chemistry to make its living.  A tremendous amount of the work that is done by the cell is accomplished by ambient heat, a property that everything on our planet has an awful lot of. This heat comes from the Earth’s molten (and radioactive) core, from the Sun’s rays and ultimately from the energy released in the big bang. Thermal energy makes the atoms and molecules in everything move and vibrate incredibly fast. Especially in the watery cytosol within the cell membrane, this molecular kinetic energy ceaselessly creates opportunities for molecules to meet and interact. Life takes advantage of this “free energy” by using it to power the work that takes place in our cells. Clearly, we get energy to do work from the food that we eat. Sugars, carbohydrates, proteins and fats are converted to ATP to power work within the cell, but ATP would be worthless if out cells didn’t have molecular kinetic energy, in the form of temperature, complements of the universe (I have never seen this point written out before, so I wanted to do so here).  
The universe is cooling down as it continues to spread out from the force, the explosion, of the big bang.  This cooling will reach absolute zero (-273 degrees Celsius) many billions of years from now at which time the heat will be zero and all atomic and molecular movement will finally cease (even though chemical energy may still be available in the bonds between existing atoms). So the free energy that we enjoy is finite but still it seems amazing how this ubiquitous movement on this tiny scale, can continue for so long, virtually unimpeded.
If you were to place a rock from your backyard in a theoretical, closed system, it would not cool. The momentum of its particles would be conserved despite the billions of collisions that take place every second.  But we all know that in large scale physical systems that are not “closed off,” energy is not well conserved. Imagine putting a number of billiard balls inside of a plastic, transparent box and shaking it vigorously. Physics tells us that the forces and energy that you applied to the box will all be conserved, accounted for in some way, somewhere. Unlike the atoms in a cell though, the kinetic energy of momentum in the balls will be transferred to other forms of energy very rapidly.  The balls will collide with each other and with the walls of the box several times where they will transfer their energy in the form of sounds (energetic vibrations in air), friction against the felt, and heat, heating up the box and the balls.  In this way, momentum is quickly taken out of systems that we observe at our large scale.

On a molecular scale though atoms collide with things and bounce off in an elastic way without losing almost any of their initial momentum.  They can transfer momentum to each other easily but it would take a staggeringly enormous amount of time for the atoms to lose all of their kinetic energy and lay motionless at the bottom of a box.  This is true no matter what phase they are in; liquid, solid or gas. The really cool thing about cells is, they take advantage of the huge number of collisions that take place inside of them due to their temperature alone. Each collision is an event that has the potential of creating an auspicious chemical reaction that will help the cell in its effort to build and thrive.  Fittingly, one of the main things that a cell builds are enzymes, tiny proteins made of thousands of atoms, that help to make the auspicious collisions thousands of times more frequent. Enzymes are chemical catalysts that speed up metabolic reactions by lowering energy barriers and orient molecules for collisions. Enzymes truly empower the cell to harness the momentum of the atoms inside of it by influencing the type of collisions that occur.
When we measure the metabolism or energy expenditure in organisms, we measure the chemical bonds made possible through photosynthesis. We don’t measure the ambient heat, which is really the energetic substrate for life on a molecular level. It would be really interesting to me to find out what really powers us more, food or all of the energy available to us in the form of molecular kinetic energy. Clearly there would potentially be many different but valid ways to measure both and clearly they interact such as when metabolism increases temperature.

1 comment:

  1. wondering if you found out what really powers us more, food or molecular kinetic energy.... though it seems that you're no longer blogging here...